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Article Contents

Molecular analysis of skeletal evidence, migrant identification, search, detection and recovery, commingling analysis, biomechanics of bone trauma, decomposition research, bone microscopy, isotope analysis, facial imaging, recent advances in forensic anthropology.

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Douglas H. Ubelaker, Recent Advances in Forensic Anthropology, Forensic Sciences Research , Volume 3, Issue 4, December 2018, Pages 275–277, https://doi.org/10.1080/20961790.2018.1466384

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Forensic anthropology involves diverse applications of anthropological knowledge to medico-legal problems. While the applications are evidence-driven, the available scientific methodology and foundation have developed through decades of research and experience. The roots of this field are anchored in comparative human anatomy but methodology has developed through experimentation, the assemblage of documented collections and databases and thoughtful research design. While forensic anthropology represents a mature scientific field, it continues to evolve and advance through new, innovative global research. Much of this progress is fuelled by issues encountered in casework. The unique evidence and problems presented in forensic cases call for the very best scientific approaches available. Usually, the correct approaches and solutions can be found in the existing scientific literature. However, sometimes the unique issues presented by the casework cannot be addressed adequately with the existing techniques. These situations stimulate forensic anthropologists to seek new solutions through targeted research.

This Special Issue presents research advances in several areas of forensic anthropology that have sustained rapid, recent progress. While our journals continually reveal new information in all aspects of forensic anthropology, several areas of investigation have registered particularly strong academic interest featuring innovative research.

Successful recovery and analysis of DNA has dramatically affected many areas of forensic science. In the field of forensic anthropology, molecular analysis can yield highly accurate information regarding the sex of the individual represented and provide positive identification [ 1 ]. Molecular approaches also can contribute to ancestry evaluation and species recognition. The use of DNA for positive identification has had a major impact on the practice of forensic anthropology and related fields of forensic science.

While the merits and contributions of DNA analysis are profound, many related issues express the need for new, innovative research and technological development. Frequently, evidence submitted for forensic anthropological analysis is not in pristine condition. In many cases, recovered remains are incomplete and/or extremely degraded due to criminal activity and/or taphonomic factors. Some site investigations produce only small fragments where even species is not apparent. Decisions need to be made regarding what areas of bone or tooth should be examined. Since DNA analysis is an expensive and destructive process, these decisions are critical and can affect the outcome of the case. Of course, decisions regarding the type of DNA analysis also are critical and largely driven by both the availability of the antemortem information and the nature of the evidence. Experimentation and casework experience have greatly improved approaches to these issues.

Deaths related to the global movement of undocumented people across national borders present major forensic challenges. Even within countries, identification of citizens can be difficult with incomplete evidence and lack of information regarding missing persons. These problems are greatly exacerbated when different countries are involved and the international movement of the person represented is not registered officially. Such cases call for extraordinary investigation, thoughtful forensic analysis and international communication. These efforts can strain the available local resources and often fall short of positive identification.

Recent years have witnessed remarkable efforts to address the identification of deceased, undocumented border crossers. These initiatives have involved international cooperation, careful exhumation procedures, comprehensive anthropological analysis and new techniques such as isotope analysis to identify the likely regions/countries of origin.

The entire process of forensic anthropological investigation begins with the procedures of search, detection and recovery. Improper or inadequate detection and recovery of human remains can compromise the downstream analysis and interpretation. While the traditional techniques of surface survey and excavation continue to be needed, new approaches, especially those using advanced technology offer significant advances.

Search procedures can be especially challenging when only very general information is available regarding the likely location of human remains. Topographic features can present limitations, especially with dense vegetation and other ground cover. Investigations of humanitarian and human rights issues can present special search and recovery challenges when information suggests that wells, cisterns, sewer systems, mass graves or disposal in water were involved. Confronted with these problems, researchers have devised innovative new approaches to improve the probability of success.

Secondary deposits of human remains or those that have sustained significant disturbance involve loss of normal bone articulation patterns. When multiple individuals are involved, the resulting commingling presents challenges to determine the number of persons represented and to assemble remains of individuals for analysis, identification and return to families. Traditional approaches to commingling problems have involved sorting by the type and side (left or right) of bone, age at death, bone size and maturation, sex and pathological conditions. In some skeletal assemblages, taphonomic indicators can be helpful as well.

Once obvious sorting has been completed, questions persist regarding bone morphology related to individuals. Could a robust femur relate to a robust humerus and represent one individual? Recent advances in commingling analysis address this issue. New databases and computerized techniques establish the probabilities that different bones could relate to the same individual. Applications refine the determination of the number of individuals represented and facilitate analysis aimed at identification.

A primary function of anthropological analysis relates to the interpretation of bone trauma. Anthropologists must differentiate the skeletal alterations representing perimortem trauma from those relating to antemortem injury, developmental features or postmortem and taphonomic factors. Assessment of the biomechanical factors involved plays a key role in any interpretation. Knowledge of biomechanical principles is required to explain fracture patterns and other alterations likely related to perimortem trauma. Interpretation of bone trauma can be challenging. Such challenges have led to greater understanding of the principles involved and experimental work designed to improve interpretation.

Major new initiatives in forensic anthropology have focused on decomposition research. Experiments involving both humans and non-human animals have revealed great detail about the process and variation of soft tissue decomposition and hard tissue alteration. In general, such research has elucidated the many factors that influence both the nature and timing of the decomposition process. Clearly temperature and location (surface, in-ground, aquatic, etc.) have long been regarded as key factors. Research has also indicated that soil conditions, moisture, body composition, body condition, presence of clothing or enclosures, funerary treatment and many other factors can influence the process. Such information is needed to properly assess time since death (post-mortem interval) and post-mortem events related to criminal activity.

In 1965, Ellis R. Kerley [ 2 ] published a technique that allowed age at death to be estimated from microscopic examination of features in human compact bone from the femur, tibia and fibula. Kerley's procedure involved the examination of primary osteons, secondary osteons, osteon fragments and the extent of remaining circumferential lamellar bone. This approach gained recognition due to its reported accuracy and the fundamental processes of bone formation and remodelling that it expressed. Since 1965, the technique has undergone many revisions and expansions for application to other bones of the skeleton. Research also has revealed how bone microscopic examination can provide useful information on many issues of forensic anthropological analysis.

For decades, analysis of elemental stable isotopes has offered key anthropological information related to diet. Stable carbon isotopes recovered from human tissues have revealed if diet focused on plants with a C 3 photosynthetic pathway or a C 4 pathway and the herbivores that fed upon them. Analysis of nitrogen isotopes provides insight into the trophic level of human diet. In anthropological studies of ancient populations, such information is crucial to interpretations of dietary and horticultural practices.

Recently, researchers have applied the concepts of isotopic analysis to examine the geographical origin of human remains. When unidentified human remains are recovered in forensic contexts, investigators question if they represent someone who lived in the area of recovery or from somewhere else. This question is especially relevant in cases involving terrorism and unidentified possible migrants. Using a battery of stable isotope analyses, researchers can determine if the isotopic signatures from the unknown match local baseline data. If not, attempts can be made to determine from what geographic area the unknown originated. This exciting new area of forensic science investigation depends on the assemblage of baseline data from appropriate geographic regions.

Forensic anthropologists relate to issues of facial imaging in facial approximation, craniofacial photographic superimposition and interpretations of surveillance images. Facial approximation refers to the process of estimating the living facial image of a person from the evidence presented by a recovered skull. This technique is used to reach out to the public for leads in missing persons that could culminate in identification using other methods.

Craniofacial photographic superimposition involves comparing a facial photograph of a missing person with a recovered skull. This technique is used primarily to exclude when photographs are available of a missing person thought perhaps to be represented by the recovered remains.

Recent research has focused on enhanced use of computers and related technology, as well as targeted efforts to clarify the relationship between soft and hard tissues. Facial approximation continues to represent a blend of art and science; however, recent advances have strengthened the scientific foundation.

Articles in this Special Issue of Forensic Sciences Research focus on overviews of the published literature on these topics. They also share results from the latest innovative research on these key areas of forensic anthropology applications.

Baker   L . Biomolecular applications . In: Blau   S   Ubelaker   DH , editors.   Handbook of forensic anthropology and archaeology . 2nd. ed. New York: Routledge ; 2016 . p. 416 – 429 .

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Kerley   ER . The microscopic determination of age in human bone . Am J Phys Anth . 1965 ; 23 : 149 – 163 .

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Scientists are fixing flawed forensics that can lead to wrongful convictions.

Police lineups, fingerprinting and trace DNA techniques all need reform

Forensic science can help solve crimes, but some techniques and methods of analysis need improvement.

The Red Dress

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By Amber Dance

June 6, 2024 at 9:00 am

Charles Don Flores has been facing death for 25 years.

Flores has been on death row in Texas since a murder conviction in 1999. But John Wixted, a psychologist at the University of California, San Diego, says the latest memory science suggests Flores is innocent.

The murder Flores was convicted of happened during a botched attempt to locate drug money. An eyewitness, a woman who looked out her window while getting her kids ready for school, told the police that two white males with long hair got out of a Volkswagen Beetle and went into the house where the killing took place. The police quickly picked up the owner of the car, a long-haired white guy.

The police also suspected Flores, who had a history of drug dealing. He was also a known associate of the car owner, but there was a glaring mismatch with the witness description: Flores is Hispanic, with very short hair.

Still, the police put a “very conspicuous” photo of him in a lineup, says Gretchen Sween, Flores’ lawyer. “His [photo] is front and center, and he’s the only one wearing this bright-colored shirt, screaming ‘pick me!’”

But the eyewitness did not pick him. It was only after some time passed, during which the witness saw Flores’ picture on the news, that she came to think he was the one who entered the house. Thirteen months after she described two white men with long hair, she testified in court that it was Flores she saw.

Memory scientists have long been mistrustful of eyewitness reports because memory is malleable. But in recent years, Wixted says, research has shown that the initial lineup — the very first memory test — can be reliable. He argues that the witness’s initial rejection of Flores’ photo is evidence of innocence.

In 2013, Texas became the first state to introduce a “junk science” law allowing the courts to reexamine cases when new science warranted it. Sween has submitted hundreds of pages of arguments to get a judge to consider this new slant on memory science. So far, the Texas authorities have remained unconvinced.

“Our criminal justice system is generally slow to respond to any kind of science-based innovation,” laments Tom Albright, a neuroscientist at the Salk Institute for Biological Studies in La Jolla, Calif.

But researchers are pushing ahead to improve the science that enters the courtroom. The fundamental question for all forms of evidence is simple, Albright says. “How do you know what is right?” Science can’t provide 100 percent certainty that, say, a witness’s memory is correct or one fingerprint matches another. But it can help improve the likelihood that evidence is tested fairly or evaluate the likelihood that it’s correct.

“Our criminal justice system is generally slow to respond to any kind of science-based innovation.” Tom Albright, neuroscientist

Some progress has been made. Several once-popular forms of forensics have been scientifically debunked, says Linda Starr, a clinical professor of law at Santa Clara University in California and cofounder of the Northern California Innocence Project, a nonprofit that challenges wrongful convictions. One infamous example is bite marks. Since the 1970s, a few dentists have contended that a mold of a suspect’s teeth can be matched to bite marks in skin, though this has never been proved scientifically. A 2009 report from the National Academy of Sciences noted how bite marks may be distorted by time and healing and that different experts often produce different findings.

More than two dozen convictions based on bite mark evidence have since been overturned, many due to new DNA evidence.

Now researchers are taking on even well-accepted forms of evidence, like fingerprints and DNA, that can be misinterpreted or misleading.

“There are a lot of cases where the prosecution contends they have forensic ‘science,’ ” Starr says. “A lot of what they’re claiming to be forensic science isn’t science at all; it is mythology.”

Do the eyes have it?

Though research has been clear about the shortcomings of eyewitness memory for decades, law enforcement has been slow to adopt best practices to reduce the risk of memory contamination, as appears likely to have happened in Flores’ case.

The justice system largely caught on to the problem of memory in the 1990s, when the introduction of DNA evidence overturned many convictions. In more than 3,500 exonerations tracked since 1989, there was some version of false identification in 27 percent of cases, according to the National Registry of Exonerations . What’s become clear is that an eyewitness’s memory can be contaminated, as surely as if someone spit into a tube full of DNA.

Over the last decade, expert groups, including the National Academy of Sciences and the American Psychological A­ssociation , have recommended that police investigators treat a lineup — usually done with photographs these days — like a controlled experiment. For example, the officer conducting the lineup should be “blind” as to which of the people is the suspect and which are “fillers” with no known link to the crime. That way, the officer cannot subconsciously influence the results.

Those best-practice recommendations are catching on, but slowly, says Gary Wells, a psychologist at Iowa State University in Ames who coauthored the American Psychological Association recommendations. “We continue to have cases popping up, sort of right and left, in which they’re doing it wrong.”

Exonerating circumstances

Of over 3,500 exonerations in the United States tracked since 1989, problems with forensic evidence and eyewitness testimony each played a role in about a quarter of the cases (exonerations can have multiple contributing factors, so the bars total more than 100 percent).

Factors contributing to exonerations since 1989

One problem arises when the filler photos don’t match the witness’s description of a suspect, or the suspect stands out in some way — as Sween contends happened with Flores. Fillers should all have the same features as the eyewitness described, and not be too similar or too different from the suspect. For now, it’s on police officers to engineer the perfect lineup, with no external check on how appropriate the fillers are.

As a solution, Albright and colleagues are working on a computer system to select the best possible filler photographs. The catch is that computer algorithms tend to focus on different facial features than humans do. So the researchers asked human subjects to rank similarity between different artificially generated faces and then used machine learning to train the computer to judge facial similarity the way people do. Using that information, the system can generate lineups — from real or AI-generated faces — in which all the fillers are more or less similar to the suspect. Next up, the scientists plan to figure out just how similar the filler faces should be to the suspect for the best possible lineup results.

Proper filler selection would help, but it doesn’t solve a key problem Wixted sees in the criminal justice system: He wants police and courts to appreciate a newer, twofold understanding of eyewitness testing. First, eyewitnesses who are confident in their identification tend to be more accurate , according to an analysis Wixted and Wells penned in 2017. For example, the pair analyzed 15 studies in which witnesses who viewed mock crimes were asked to report their confidence on a 100-point scale. Across those studies, the higher witnesses rated their own confidence, the more likely they were to identify the proper suspect. Accurate eyewitnesses also tend to make decisions quickly, because facial memory happens fast: “seconds, not minutes,” Wixted says.

Conversely, low confidence indicates the identification isn’t too reliable. In trial transcripts from 92 cases later overturned by DNA evidence, most witnesses who thought back to the first lineup recalled low confidence or outright rejection of all options, according to research by Brandon Garrett, a law professor at Duke University.

The confidence correlation is appropriate only when the lineup is conducted according to all best practices, which remains a rare occurrence, warns Elizabeth Loftus, a psychologist at the University of California, Irvine. But Wixted argues it’s still relevant, if less so, even in imperfect lineups.

The second recent realization is that the very first lineup a witness sees, assuming police follow best practices to avoid biasing the witness, has the lowest chance of contamination. So a witness’s memory should be tested just once . “There’s no do-overs,” Wixted says.

Together, these factors suggest that a confident witness on the first, proper lineup can be credible, but that low confidence or subsequent lineups should be discounted.

Those recommendations come mainly from lab experiments. How does witness confidence play out in the real world ? Wells tested this in a 2023 study with his graduate student Adele Quigley-McBride, an experimental psychologist now on the faculty at Simon Fraser University in Burnaby, Canada. They obtained 75 audio recordings of witness statements during real, properly conducted lineups. While the researchers couldn’t be sure that the suspects were truly the criminals, they knew that any filler identification must be incorrect because those people were not connected to the crime in any way.

Face-to-face

During a photo lineup, an eyewitness is shown a suspect’s photo and filler photos, either simultaneously or sequentially, and asked to ID the suspect. An alternative approach doesn’t ask a witness to make an identification. Instead, the witness views pairs of photos, some of which include the suspect and some of which don’t. For each pair, the witness judges which person looks more like the potential perp. The procedure ranks each lineup face to see if the suspect was overall judged as most similar to who the witness saw.

Volunteers listened to those lineup recordings and rated witness confidence. Witnesses who quickly and confidently picked a face — within about half a minute or less — were more likely to pick the suspect than a filler image. In one experiment, for example, the identifications that ended on a suspect had been rated, on average, as 69 percent confident, as opposed to about 56 percent for those that ended up on a filler. Quigley-McBride proposes that timing witness decisions and recording confidence assessments could be valuable information for investigators.

Witnesses also bring their own biases. They may assume that since the police have generated a lineup, the criminal must be in it. “It’s very difficult to recognize the absence of the perpetrator,” Wells says.

In a 2020 study, Albright used the science of memory and perception to design an approach that might sidestep witness bias , by not asking witnesses to pick out a suspect from a lineup at all. Instead, the eyewitness views pairs of faces one at a time. Some pairs contain the suspect and a filler; some contain two fillers. For each pair, the witness judges which person looks more like the remembered perpetrator. Based on those pairwise “votes,” the procedure can rank each lineup face and determine if the suspect comes out as most similar. “It’s just as good as existing methods and less susceptible to bias,” Albright says.

Wixted says the approach is “a great idea, but too far ahead of its time.” Defense attorneys would likely attack any evidence that lacks a direct witness identification.

Putting fingerprints to the test

Fingerprints have been police tools for a long time, more than a century. They were considered infallible for much of that history.

Limitations to fingerprint analysis came to light in spectacular fashion in 2004, with the bombing of four commuter trains in Madrid. Spanish police found a blue plastic bag full of detonators and traces of explosives. Forensic experts used a standard technique to raise prints off the bag: fumigating it with vaporized superglue, which stuck to the finger marks, and staining the bag with fluorescent dye to reveal a blurry fingerprint.

Running that print against the FBI’s fingerprint database highlighted a possible match to Brandon Mayfield, an Oregon lawyer. One FBI expert, then another, then another confirmed Mayfield’s print matched the one from the bag.

Mayfield was arrested. But he hadn’t been anywhere near Madrid during the bombing. He didn’t even possess a current passport. Spanish authorities later arrested someone else, and the FBI apologized to Mayfield and let him go.

The case highlights an unfortunate “paradox” resulting from fingerprint databases, in that “the larger the databases get … the larger the probability that you find a spurious match,” says Alicia Carriquiry. She directs the Center for Statistics and Applications in Forensic Evidence, or CSAFE, at Iowa State University.

In fingerprint analyses , the question at hand is whether two prints, one from a crime scene and one from a suspect or a fingerprint database, came from the same digit ( SN: 8/26/15 ). The problem is that prints lifted from a crime scene are often partial, distorted, overlapping or otherwise hard to make out. The expert’s challenge is to identify features called minutiae, such as the place a ridge ends or splits in two, and then decide if they correspond between two prints.

Studies since the Madrid bombing illustrate the potential for mistakes. In a 2011 report, FBI researchers tested 169 experienced print examiners on 744 fingerprint pairs, of which 520 pairs contained true matches. Eighty-five percent of the examiners missed at least one of the true matches in a subset of 100 or so pairs each examined. Examiners can also be inconsistent : In a subsequent study, the researchers brought back 72 of those examiners seven months later and gave them 25 of the same fingerprint pairs they saw before. The examiners changed their conclusions on about 10 percent of the pairings.

Forensic examiners can also be biased when they think they see a very rare feature in a fingerprint and mentally assign that feature a higher significance than others, Quigley-McBride says. No one has checked exactly how rare individual features are, but she is part of a CSAFE team quantifying these features in a database of more than 2,000 fingerprints.

Computer software can assist fingerprint experts with a “sanity check,” says forensic scientist Glenn Langenburg, owner of the consulting firm Elite Forensic Services in St. Paul, Minn. One option is a program known rather informally as Xena (yes, for the television warrior princess) developed by Langenburg’s former colleagues at the University of Lausanne in Switzerland.

Xena’s goal is to calculate a likelihood ratio, a number that compares the probability of a fingerprint looking like it does if it came from the suspect (the numerator) versus the probability of the fingerprint looking as it does if it’s from some random, unidentified individual (the denominator). The same type of statistic is used to support DNA evidence.

To compute the numerator probability, the program starts with the suspect’s pristine print and simulates various ways it might be distorted, creating 700 possible “pseudomarks.” Then Xena asks, if the suspect is the person behind the print from the crime scene, what’s the probability any of those 700 could be a good match?

To calculate the denominator probability, the program compares the crime scene print to 1 million fingerprints from random people and asks, what are the chances that this crime scene print would be a good match for any of these?

If the likelihood ratio is high, that suggests the similarities between the two prints are more likely if the suspect is indeed the source of the crime scene print than if not. If it’s low, then the statistics suggest it’s quite possible the print didn’t come from the suspect. Xena wasn’t available at the time of the Mayfield case, but when researchers ran those prints later, it returned a very low score for Mayfield, Langenburg says.

Another option, called FRStat , was developed by the U.S. Army Criminal Investigation Laboratory. It crunches the numbers a bit differently to calculate the degree of similarity between fingerprints after an expert has marked five to 15 minutiae.

While U.S. Army courts have admitted FRStat numbers, and some Swiss agencies have adopted Xena, few fingerprint examiners in the United States have taken up either. But Carriquiry thinks U.S. civilian courts will begin to use FRStat soon.

Trace DNA makes for thin evidence

When DNA evidence was first introduced in the late 20th century, courts debated its merits in what came to be known as the “DNA wars.” The molecules won, and DNA’s current top status in forensic evidence is well-deserved — at least when it’s used in the most traditional sense ( SN: 5/23/18 ).

Forensic scientists traditionally isolate DNA from a sample chock-full of DNA, like bloodstains or semen from a rape kit, and then focus in on about 20 specific places in the genomic sequence. These are spots where the genetic letters repeat like a stutter, such as GATA GATA GATA. People can have different numbers of repeats in each spot. If the profiles are the same between the suspect and the crime scene evidence, that doesn’t confirm the two people are one and the same. But because scientists have examined the stutter spots in enough human genomes, they can calculate a likelihood ratio and testify based on that.

So far, so good. That procedure can help juries answer the question, “Whose DNA is this?” says Jarrah Kennedy, a forensic DNA scientist at the Kansas City Police Crime Laboratory.

But in recent years, the technology has gotten so sensitive that DNA can now be recovered from even scant amounts of biological material. Forensic scientists can pluck a DNA fingerprint out of just a handful of skin cells found on, say, the handle of a gun. Much of Kennedy’s workload is now examining this kind of trace DNA, she says.

“Human people do this work, and human people make mistakes and error.” Tiffany Roy, forensic DNA expert

The analysis can be tricky because DNA profiles from trace evidence are less robust. Some stutter numbers might be missing; contamination by other DNA could make extra ones appear. It’s even more complicated if the sample contains more than one person’s DNA. This is where the examiner’s expertise, and opinions, come into their assessments.

“Human people do this work, and human people make mistakes and errors,” says Tiffany Roy, a forensic DNA expert and owner of the consulting firm ForensicAid in West Palm Beach, Fla.

And even if Roy or Kennedy can find a DNA profile on trace evidence, such small amounts of DNA mean they haven’t necessarily identified the profile of the culprit of a crime. Did the suspect’s DNA land on the gun because they pulled the trigger? Or because they handled the weapon weeks before it ever went off?

“It’s not about the ‘who?’ anymore,” Kennedy says. “It’s about ‘how?’ or ‘when?’ ”

Such DNA traces complicated the case of Amanda Knox, the American exchange student in Italy who was convicted in 2009, with two others, of sexually assaulting and killing her roommate. DNA profiles from Knox and her boyfriend were found on the victim’s bra clasp and a knife handle. But experts later deemed the DNA evidence weak: There was a high risk the bra clasp had been contaminated over the weeks it sat at the crime scene, and the signal from the knife was so low, it may have been incorrect. The pair were acquitted, upon appeal, in 2015.

Here, again, statistical software can help forensic scientists decide how many DNA profiles contributed to a mixture or to calculate likelihood ratios. But Roy estimates that only about half of U.S. labs use the most up-to-date tools. “It keeps me awake at night.”

And Roy suspects the courts may at some point have to consider whether science can inform how a person’s DNA got on an item. Thus, she says, “I think there’s a new DNA war coming.” She doesn’t think the science can go that far.

When science saves the day

Change happens slowly, Wixted says. And Flores and others remain incarcerated despite efforts by Sween and others questioning faulty evidence.

One reason U.S. courts often lag behind the science is that it’s up to the judge to decide whether any specific bit of evidence is included in a trial. The federal standard on expert testimony, known as Rule 702 and first set out in 1975, is generally interpreted to mean that judges must assess whether the science in question is performed according to set standards, has a potential or known error rate, and has been through the wringer of scientific peer review. But in practice, many judges don’t do much in the way of gatekeeping. Last December, Rule 702 was updated to reemphasize the role of judges in blocking inappropriate science or experts.

In Texas, Sween says she’s not done fighting for Flores, who’s still living in a six-by-nine-foot cell on death row but has graduated from a faith-based rehabilitation program and started a book club with the help of someone on the outside. “He’s a pretty remarkable guy,” Sween says.

But in another case Wixted was involved with, the new memory science led to a happier ending.

Miguel Solorio was arrested in 1998, suspected of a drive-by shooting in Whittier, Calif. His girlfriend — now wife — provided an alibi. Four eyewitnesses, the first time they saw a lineup, didn’t identify him. But the police kept offering additional lineups, with Solorio in every one. Eventually, two witnesses identified him in court. He was convicted and sentenced to life in prison without parole.

When the Northern California Innocence Project and the Los Angeles County District Attorney’s Office took a fresh look at the case, they realized that the eyewitnesses’ memories had been contaminated by the repeated lineups. The initial tests were “powerful evidence of Mr. Solorio’s innocence,” the district attorney wrote in an official concession letter.

Last November, Solorio walked out of prison, a free man.

Investigating crime science

Some forensic techniques that seem scientific have been criticized as subjective and had their certainty questioned. That doesn’t necessarily mean they are never brought into court or that they’re meritless. For some techniques, researchers are studying how to make them more accurate.

Hair analysis

Experts judge traits such as color, texture and microscopic features to see if it’s possible a hair came from a suspect, but not to make a direct match. Analysis of DNA from hair has largely supplanted physical examination. But if no root is present, authorities won’t be able to extract a complete DNA profile. Scientists at the National Institute of Standards and Technology are analyzing whether certain hair proteins , which vary from person to person, can be correlated with a suspect’s own hair protein or DNA profile.

Fire scene investigation

Fire investigators once thought certain features, such as burn “pour patterns,” indicated an arsonist used fuel to spur a fast-spreading fire. In fact, these and other signs once linked to arson can appear in accidental fires, too, for example due to high temperatures or water from a firefighter’s hose. A 2017 report from the American Association for the Advancement of Science said identifying a fire’s origin and cause “can be very challenging and is based on subjective judgments and interpretations.”

Firearms analysis

A gun’s internal parts leave “toolmarks” on the bullet. Examiners study these microscopic marks to decide whether two bullets probably came from the same gun. A 2016 President’s Council of Advisors on Science and Technology report said the practice “falls short of the scientific criteria for foundational validity.” In 2023, a judge ruled for the first time that this kind of evidence was inadmissible. Researchers at NIST and the Center for Statistics and Applications in F­orensic Evidence, or CSAFE, are developing automated, quantifiable methods to improve objectivity.

Bloodstain pattern analysis

Experts examine blood pooled or spattered at a crime scene to determine the cause, such as stabbing, and the point of origin, such as the height the blood came from. While some of this is scientifically valid, the analysis can be complex, with overlapping blood patterns. In 2009, the National Academy of Sciences warned that “some experts extrapolate far beyond what can be supported.” CSAFE has compiled a blood spatter database and is working on more objective approaches.

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• How Reliable Is Forensic Evidence

Open for Discussion: How Reliable Is Forensic Evidence?

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By Brian Rohrig   October 2016

In what has been dubbed the “CSI Effect,” juries place a high premium on forensic evidence presented by an expert witness. After all, it is hard to argue with science. On television shows, forensic evidence gathered at the crime scene often puts away the bad guys. How reliable is this forensic evidence?

Many people are surprised to learn that any type of evidence collected by a forensic investigator, such as fingerprints, blood, and hair, will always be circumstantial. Circumstantial evidence requires interpretation, and its presence does not necessarily imply guilt. In order for this type of evidence to be used effectively, a case must be constructed. Forensic evidence may form part of a case, but it is not the whole case.

Blood and hair analysis

To understand the limitations of forensic evidence, it is necessary to distinguish between class evidence and individual evidence. Class evidence consists of substances such as blood and hair, which can be used to place an individual in a general class but cannot be used to identify an individual. For example, blood typing can be used to establish whether someone has A, B, AB, or O blood, but cannot point to a person.

A common method to test for blood is to spray an area with a solution of luminol and hydrogen peroxide. If blood is present, the iron atoms within the hemoglobin molecules in red blood cells act as a catalyst, causing the luminol to emit an eerie blue glow.  This chemical reaction is a great way to test for blood stains.  However, other compounds can also catalyze this reaction.  A number of other substances, from bleach to horseradish, can also produce an eerie blue glow, leading a forensic investigator to conclude that blood is present when, in fact, there is none.

Fingerprint and DNA analysis

On the other hand, individual evidence, such as fingerprints and DNA, can be used to identify an individual. Each DNA molecule is a polymer, which consists of millions of repeating units known as nucleotides.  Even though 99.9% of a person’s DNA is identical to any other person’s, there are minor variations in the composition and arrangement of the various nucleotides, making each person’s DNA uniquely their own.

However, DNA is often used to exclude a suspect rather than confirm one. When DNA tests are run on a sample, only a small fragment of DNA is sequenced, not the entire genome. When collecting DNA at a crime scene, it is sometimes difficult to obtain samples that are not contaminated with another person’s DNA, making results unreliable. Over time, DNA degrades. The laboratory technicians who run the tests sometimes make mistakes. The final determination about whether a DNA profile matches that of a suspect is subject to interpretation.

Forensic chemistry

Chemistry plays an indispensable role in forensic science, which is playing an increasingly vital role in our judicial system. Every type of forensic evidence—from fingerprints to blood to DNA—all involve chemistry. But forensic science alone cannot be used to establish guilt. Any judicial system is, above all, a human endeavor, and humans will always be fallible.  

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Recent advances in forensic biology and forensic DNA typing: INTERPOL review 2019–2022

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This review paper covers the forensic-relevant literature in biological sciences from 2019 to 2022 as a part of the 20th INTERPOL International Forensic Science Managers Symposium. Topics reviewed include rapid DNA testing, using law enforcement DNA databases plus investigative genetic genealogy DNA databases along with privacy/ethical issues, forensic biology and body fluid identification, DNA extraction and typing methods, mixture interpretation involving probabilistic genotyping software (PGS), DNA transfer and activity-level evaluations, next-generation sequencing (NGS), DNA phenotyping, lineage markers (Y-chromosome, mitochondrial DNA, X-chromosome), new markers and approaches (microhaplotypes, proteomics, and microbial DNA), kinship analysis and human identification with disaster victim identification (DVI), and non-human DNA testing including wildlife forensics. Available books and review articles are summarized as well as 70 guidance documents to assist in quality control that were published in the past three years by various groups within the United States and around the world.

1. Introduction

This review explores developments in forensic biology and forensic DNA analysis of biological evidence during the years 2019–2022. In some cases, there may be overlap with 2019 articles mentioned in the previous INTERPOL review covering 2016 to 2019 [ 1 ]. This review includes books and review articles, published guidance documents to assist in quality control, rapid DNA testing, using law enforcement DNA databases plus investigative genetic genealogy DNA databases along with privacy/ethical issues, forensic biology and body fluid identification, DNA extraction and typing methods, mixture interpretation involving probabilistic genotyping software (PGS), DNA transfer and activity level evaluations, next-generation sequencing (NGS), DNA phenotyping, lineage markers (Y-chromosome, mitochondrial DNA, X-chromosome), new markers and approaches (microhaplotypes, proteomics, and microbial DNA), kinship analysis and human identification with disaster victim identification (DVI), and non-human DNA testing including wildlife forensics.

Multiple searches, using the Scopus (Elsevier) and Web of Science (Clarivate) databases, were conducted in the first half of 2022 with “forensic” and “DNA” or “biology” and “2019 to 2022” as search options. Over 4000 articles were returned with these searches. Through visual examination of titles and authors, duplicates were removed, and articles sorted into 32 subcategories to arrive at a list of almost 2000 publications that were supplemented throughout the remainder of the year as this review was being prepared. The tables of contents for non-indexed journals, such as WIRES Forensic Science , Journal of Forensic Identification , and Forensic Genomics were also examined to locate potentially relevant articles.

For example, a Scopus search conducted on June 13, 2022, using “forensic DNA” and “2019 to 2022” found a total of 3059 documents. Table 1 lists the top ten journals from this search. The Forensic Science International: Genetics Supplement Series (see row #4 in Table 1 ) provides the proceedings of the International Society for Forensic Genetics (ISFG) meeting held in Prague in September 2019. This volume contains 914 pages with 347 articles (although only 172 showed up in the Scopus search) that are freely available at https://www.fsigeneticssup.com /[ 2 ]. Thus, searches conducted with one or even multiple databases (e.g., Scopus and Web of Science) may not be comprehensive or exhaustive.

Top ten journals with forensic DNA articles published from 2019 to 2022 based on a Scopus search on June 13, 2022.

1.1. Books, special issues, and review articles of note

Books published during the period of this review relating to forensic biology and forensic DNA include Essential Forensic Biology, Third Edition [ 3 ], Principles and Practices of DNA Analysis: A Laboratory Manual for Forensic DNA Typing [ 4 ], Forensic DNA Profiling: A Practical Guide to Assigning Likelihood Ratios [ 5 ], Forensic Practitioner's Guide to the Interpretation of Complex DNA Profiles [ 6 ], Silent Witness: Forensic DNA Evidence in Criminal Investigations and Humanitarian Disasters [ 7 ], Mass Identifications: Statistical Methods in Forensic Genetics [ 8 ], Probability and Forensic Evidence: Theory, Philosophy, and Applications [ 9 ], Interpreting Complex Forensic DNA Evidence [ 10 ], Understanding DNA Ancestry [ 11 ], Understanding Forensic DNA [ 12 ], and Handbook of DNA Profiling [ 13 ]. The 2022 Handbook of DNA Profiling spans two volumes and 1206 pages with 54 chapters from 115 contributors representing 17 countries.

Over the past three years, several special issues on topics related to forensic biology were published in Forensic Science International: Genetics and Genes . These special issues were typically collated virtually rather than physically as invited articles were published online over some period of time and then bundled together virtually as a special issue. Some of these review articles or a set of special issue articles are open access (i.e., the authors paid a publication fee so that the article would be available online for free to readers).

During the time frame of this INTERPOL DNA review, FSI Genetics published two special issues: (1) “Trends and Perspectives in Forensic Genetics” (editor: Manfred Kayser) 1 with nine review and two original research articles published between September 2018 and January 2019, and (2) “Forensic Genetics – Unde venisti et quo vadis?” [Latin for “where did you come from and where are you going?”] (editor: Manfred Kayser) with nine articles published in 2021 and early 2022 and likely two more before the end of 2022. Topics for review articles in these special issues include DNA transfer [ 14 ], probabilistic genotyping software [ 15 ], microhaplotypes in forensic genetics [ 16 ], investigative genetic genealogy [ 17 ], forensic proteomics [ 18 ], distinguishing male monozygotic twins [ 19 ], and using the human microbiome for estimating post-mortem intervals and identifying individuals, tissues, or body fluids [ 20 , 21 ]. All of these topics will be discussed later in this article.

A Genes special issue “Forensic Genetics and Genomics” (editors: Emiliano Giardina and Michele Ragazzo) 2 published 11 online articles plus an editorial from April 2020 to January 2021 while another Genes special issue “Forensic Mitochondrial Genomics” (editors: Mitch Holland and Charla Marshall) 3 compiled 11 articles from February 2020 to April 2021. An “Advances in Forensic Genetics” Genes special issue (editor: Niels Morling) 4 included 25 articles shared between April 2021 and May 2022. In July 2022, the Advances in Forensic Genetics articles were compiled as a 518-page book. 5 Other Genes special issues in development or forthcoming covering aspects of forensic DNA and requesting potential manuscripts by late 2022 or early 2023 include “State-of-the-Art in Forensic Genetics” (editor: Chiara Turchi), 6 “Trends in Population Genetics and Identification—Impact on Anthropology (editors: Antonio Amorim, Veronica Gomes, Luisa Azevedo), 7 “Identification of Human Remains for Forensic and Humanitarian Purposes: From Molecular to Physical Methods” (editors: Elena Pilli, Cristina Cattaneo), 8 “Improved Methods in Forensic and DNA Analysis” (editor: Marie Allen), 9 “Forensic DNA Mixture Interpretation and Probabilistic Genotyping” (editor: Michael Coble) 10 , and “Advances in Forensic Molecular Genetics” (editors: Erin Hanson and Claire Glynn). 11 There has been a proliferation of review articles and special issues in this field in the past several years!

A new journal Forensic Science International: Reports was launched in November 2019. As of June 2022, it has published 89 articles involving DNA, most of which are descriptions of population genetic data. Likewise, a June 27, 2022, PubMed search with “forensic DNA” and the journal “Genes” found 88 articles – many of which are part of the previously mentioned special issues.

1.2. Guidance documents

Numerous documentary standards and guidance documents related to forensic DNA have been published by various organizations around the world. Table 2 lists 70 such documents released in the past three years (2019–2022) in the United States, UK, Australia, and the European Union.

Guidance documents related to forensic DNA published from 2019 to 2022. The titles are hyperlinked to available documents. Abbreviations: FBI (Federal Bureau of Investigation), CODIS (Combined DNA Index System), SWGDAM (Scientific Working Group on DNA Analysis Methods), NGS (next generation sequencing), US DOJ (United States Department of Justice), ULTR (Uniform Language for Testimony and Reports), AABB (Association for the Advancement of Blood and Biotherapies), ASB (Academy Standards Board), OSAC (Organization of Scientific Area Committees for Forensic Science), UKFSR (United Kingdom Forensic Science Regulator), ENFSI (European Network of Forensic Science Institutes), NIFS (National Institute of Forensic Science), ISFG (International Society for Forensic Genetics).

1.2.1. SWGDAM, FBI, and other US DOJ activities

The Federal Bureau of Investigation (FBI) Laboratory funds the Scientific Working Group on DNA Analysis Methods (SWGDAM) 12 to serve as a forum for discussing, sharing, and evaluating forensic biology methods, protocols, training, and research. In addition to creating guidelines on various topics, SWGDAM, which meets semiannually in January and July, provides recommendations to the FBI Director on the Quality Assurance Standards (QAS) used to assess U.S. forensic DNA laboratories involved in the National DNA Index System (NDIS) that perform DNA databasing and forensic casework. New versions of the QAS became effective July 1, 2020.

SWGDAM work products from the timeframe of 2019–2022 (see Table 2 ) include QAS audit and guidance documents, mitochondrial DNA analysis and short tandem repeat (STR) interpretation guideline revisions related to next-generation sequencing (NGS), training and Y-chromosome interpretation guidelines, a Y-chromosome Haplotype Reference Database (YHRD) update for U.S. laboratories, and reports on investigative genetic genealogy and Y-screening of sexual assault evidence kits. These documents are all accessible online. 13

In January 2022, the FBI produced a 13-page guide 14 on rapid DNA testing describing booking station applications and their vision for future integration of crime scene sample analysis and the Combined DNA Index System (CODIS), which builds on a joint position statement published in July 2020 by leaders of U.S. and European groups [ 22 ]. In addition, the FBI has shared guidance on their website for non-CODIS use of rapid DNA testing with law enforcement applications 15 and considerations for court. 16

United States Department of Justice (US DOJ) Uniform Language for Testimony and Reports (ULTRs), 17 contain three ULTRs for the forensic DNA discipline that became effective in March 2019: autosomal DNA with probabilistic genotyping, mitochondrial DNA, and Y-STR DNA. USDOJ also released an interim policy on investigative genetic genealogy in November 2019 [ 23 ] along with an opinion piece in the journal Science calling for responsible genetic genealogy [ 24 ].

Other agencies within US DOJ, namely the Bureau of Justice Assistance (BJA) and the National Institute of Justice (NIJ), published a guide for prosecutors on triaging forensic evidence [ 25 ] and best practices for improving DNA laboratory process efficiency [ 26 ]. A 200-page report to Congress on the needs assessment of forensic laboratories and medical examiner/coroner offices was released in December 2019 calling for $640 million annually in additional funding to support U.S. forensic efforts [ 27 ].

In September 2021, the Forensic Technology Center of Excellence (FTCOE), which is funded by NIJ, published a 29-page implementation strategy on next-generation sequencing for DNA analysis that was written by the NIJ Forensic Laboratory Needs Technology Working Group (FLN-TWG) [ 28 ]. In May 2022, FTCOE released a 50-page landscape study examining technologies and automation for differential extraction and sperm separation used in sexual assault investigations [ 29 ]. An introduction to forensic genetic genealogy was released in September 2022 [ 30 ].

The FTCOE also published a human factors forensic science sourcebook 18 in March 2022 through open access articles in the journal Forensic Science International: Synergy . This sourcebook, which has general applicability rather than being specific to forensic DNA analysts, includes an overview article [ 31 ] along with articles on personnel selection and assessment [ 32 ], the benefits of committing errors during training [ 33 ], how characteristics of human reasoning and certain situations can contribute to errors [ 34 ], stressors that impact performance [ 35 ], and the impact of communication between forensic analysts and detectives using a new metaphor [ 36 ].

1.2.2. OSAC and ASB activities

The Organization of Scientific Area Committees for Forensic Science (OSAC) 19 is congressionally-funded and administered by the Special Programs Office within the National Institute of Standards and Technology (NIST). OSAC consists of a governing board and over 600 members and associates organized into seven scientific area committees (SACs) and 22 subcommittees. The Biology SAC is divided into human and wildlife forensic biology activities. The Human Forensic Biology Subcommittee 20 focuses on standards and guidelines related to training, method development and validation, data analysis, interpretation, and statistical analysis as well as reporting and testimony for human forensic serological and DNA testing. The Wildlife Forensics Subcommittee 21 works on standards and guidelines related to taxonomic identification, individualization, and geographic origin of non-human biological evidence based on morphological and genetic analyses.

The Academy Standards Board (ASB) 22 is a wholly owned subsidiary of the American Academy of Forensic Sciences (AAFS) and was established as a standards developing organization (SDO). In 2015, ASB was accredited as an SDO by the American National Standards Institute (ANSI). The ASB DNA Consensus Body, with a membership consisting of practitioners, researchers, and lawyers, develops standards and guidelines related to the use of DNA in legal proceedings. Many of the documents developed by ASB were originally proposed OSAC standards or guidelines.

The OSAC Registry 23 is a repository of high-quality and technically-sound standards (both published and proposed) that are intended for implementation in forensic science laboratories. As of July 2022, the OSAC Registry contains 11 standards published by ASB as well as two (2) proposed OSAC standards or best practice recommendations related to human forensic biology. Another four ASB standards and two proposed OSAC standards related to wildlife forensic biology are on the OSAC Registry. The ASB standards issued in the past three years related to human forensic biology cover interpretation and comparison protocols, training in various parts of the process, and validation of forensic serological and DNA analysis methods as well as probabilistic genotyping systems (see Table 2 for names of these documents). A number of other documents 24 related to serological testing methods, assigning propositions for likelihood ratios in forensic DNA interpretations, validation of forensic DNA methods and software, familial DNA searching, management and use of quality assurance DNA elimination databases, setting thresholds, evaluative forensic DNA testimony, and training in use of statistics are in development within OSAC and ASB.

Additional work products of OSAC include (1) a lexicon 25 with 3282 records (although multiple records may exist for the same word, e.g., there are five definitions provided for “validation” from various sources), (2) a 35-page technical guidance document 26 on human factors in validation and performance testing that describes key issues in designing, conducting, and reporting validation research, (3) a listing of research and development needs in forensic science 27 including 18 identified by the OSAC Human Forensic Biology Subcommittee during their deliberations ( Table 3 ), and (4) process maps for several forensic disciplines including a 42-page depiction of current practices and decisions in human forensic DNA analysis released in May 2022 [ 37 ]. As a visual representation of critical steps and decision points, a process map is intended to help improve efficiencies and reduce errors, and highlight gaps where further research or standardization would be beneficial. Process maps can assist with training new examiners and enable development of specific laboratory policies or help identify best practices for the field.

Research and development needs in forensic biology as identified by the OSAC Human Forensic Biology Subcommittee (as of July 2022, see https://www.nist.gov/osac/osac-research-and-development-needs ).

1.2.3. UK Forensic Science Regulator

The UK Forensic Science Regulator (UKFSR) oversees forensic science efforts in England, Wales, and Northern Ireland. In March 2021, the Regulator released the seventh issue 28 of the Codes of Practice and Conduct for forensic science providers and practitioners in the criminal justice system. This 114-page document, which has been updated every few years, provides the overall framework for forensic science activities in the UK with other supporting guidance documents on specific areas like DNA analysis or general tasks like validation. In September 2020, a number of the Regulator documents were revised and reissued. As noted in Table 2 (see rows with documents containing “Issue 1” in the title), new guidance documents were also released in the past few years on sexual assault examinations, development of evaluative opinions, proficiency testing for DNA mixture interpretation, Y-STR profiling, DNA relationship testing, and methods employing rapid DNA testing devices. Table 2 lists 20 guidance documents pertinent to forensic biology from the UKFSR.

1.2.4. European Union and Australia

The European Network of Forensic Science Institutes (ENFSI) DNA Working Group published two documents in the past three years: one on DNA database management and the other on training of staff in forensic DNA laboratories (see Table 2 ). A best practice manual for human forensic biology and DNA profiling is also under development.

The Australian National Institute of Forensic Science (NIFS) published three documents of relevance to forensic biology on case record review, empirical study design, and transitioning technology from the laboratory to the field (see Table 2 ).

1.2.5. Other international efforts

The Association for the Advancement of Blood and Biotherapies (AABB) 29 published the 15th edition of their Standard for Relationship Testing Laboratories, which became effective on January 1, 2022. This documentary standard was developed by the AABB Relationship Testing Standards Committee and applies to laboratories accredited for paternity testing and other forms of genetic relationship assessment.

The International Society for Forensic Genetics (ISFG) DNA Commission 30 published two articles during the timeframe of this INTERPOL review (see Table 2 ). In 2020, guidelines and considerations were published on evaluating DNA results under activity level propositions [ 38 ]. In addition, the state of the field regarding interpretation of Y-STR results was examined along with different approaches for haplotype frequency estimation using population data – with the Discrete Laplace approach being recommended [ 39 ]. Future ISFG DNA Commission efforts will address STR allele sequence nomenclature and phenotyping.

2. Advancements in current practices

This section (Section 2 ) is intended to be law enforcement and practitioner-focused through examination of advances in current practices. The following section (Section 3 ) is intended to be researcher-focused through emphasis on emerging technologies and new developments. In this section, topics specifically covered include rapid DNA analysis, use of DNA databases to aid investigations (including familial searching, investigative genetic genealogy, genetic privacy and ethical concerns, and sexual assault kit testing), body fluid identification, DNA extraction and typing methods, and DNA interpretation at the sub-source and activity level.

2.1. Rapid DNA analysis

Rapid DNA instruments that provide integrated “swab-in-profile-out” results in 90 min or less can be used in police booking station environments and assist investigations outside of a traditional laboratory environment. These instruments were initially designed for analysis of buccal swabs to help speed processing of reference samples associated with criminal cases. Such samples are expected to contain relatively large quantities of DNA from a single contributor. Some attempts to extend the range of sample types to low quantities of DNA or mixtures have been published with various levels of success (see Table 4 ). Researcher and practitioners from Australia [ [40] , [41] , [42] ], Canada [ 43 ], China [ 44 ], Italy [ 45 ], Japan [ 46 , 47 ], and the United States [ [48] , [49] , [50] , [51] , [52] , [53] , [54] , [55] , [56] , [57] ] have contributed to an increased understanding of rapid DNA testing capabilities and limitations.

Summary of 20 rapid DNA instrument validation and evaluation studies published from 2019 to 2022. Abbreviations: A-Chip (arrestee cartridge, designed for high-quantity DNA samples), I-Chip (investigative cartridge, designed for low-quantity DNA samples), ACE (arrestee cartridge with GlobalFiler STR markers), RapidINTEL (uses 32 rather than 28 PCR cycles to increase success with low-quantity DNA samples). A-Chip and I-Chip amplify the FlexPlex set of 23 autosomal STRs, three Y-STRs, and amelogenin [ 51 ]. ACE and RapidINTEL utilize the GlobalFiler set of 21 autosomal STRs, one Y-STR, one Y-chromosome InDel, and amelogenin.

The Accelerated Nuclear DNA Equipment (ANDE) 6C (ANDE, Longmont, CO, USA) and the RapidHIT ID (Thermo Fisher Scientific, Waltham, MA, USA) are the current 31 commercially available rapid DNA systems. Each system consists of a swab for introducing the sample, a cartridge or biochip with pre-packed reagents, the instrument, and analysis software with an expert system for automated STR allele calling. Different sample cartridges can be run on each system depending on the sample type and expected quantity of DNA.

For ANDE, the arrestee cartridge (A-Chip), can accommodate up to five samples and is intended for relatively high quantities of DNA typically collected from reference buccal swabs, while the investigative cartridge (I-Chip), can process up to four samples and is intended for lower quantities of DNA that might be present in casework or disaster victim identification samples. Both ANDE cartridges use the FlexPlex27 STR assay that tests 23 autosomal STR loci, three Y-chromosome STRs, and amelogenin to generate data compatible with DNA databases around the world [ 51 ]. The RapidHIT ID ACE cartridge and RapidINTEL cartridge serve similar purposes as the ANDE A-Chip and I-Chip using GlobalFiler Express kit markers (21 autosomal STRs, DYS391, a Y-chromosome insertion/deletion marker, and amelogenin) instead of the FlexPlex assay. The ACE sample cartridge uses buccal swabs while the EXT sample cartridge processes DNA extracts [ 56 ]. Sensitivity is enhanced in the RapidINTEL cartridge by increasing the number of PCR cycles from 28 to 32 and decreasing the lysis buffer volume from 500 μL to 300 μL compared to the ACE cartridge parameters [ 46 ].

With rapid DNA testing's swab-in and answer-out integrated configuration, limited options exist for testing conditions (e.g., either A-Chip or I-Chip with ANDE). Therefore, users should evaluate performance for the sample types they desired to routinely test in their specific environment. Table 4 summarizes recently published studies containing rapid DNA assessments.

National DNA Index System (NDIS) approval has been provided by the FBI Laboratory for accredited forensic DNA laboratories to use either the ANDE 6C or RapidHIT ID Systems (A-Chip and ACE cartridges only) 32 with eligible reference mouth swabs. As noted in Table 2 , the FBI.gov website contains three documents related to rapid DNA testing: “Non-CODIS Rapid DNA Considerations and Best Practices for Law Enforcement Use” (7-pages), “Rapid DNA Testing for Non-CODIS Uses: Considerations for Court” (5-pages), and “A Guide to All Things Rapid DNA” (13-pages) in January 2022 to provide information on the topic to law enforcement agencies.

The ENFSI DNA Working Group, SWGDAM, and an FBI Rapid DNA Crime Scene Technology Advancement Task Group co-published a position statement on the use of rapid DNA testing from crime scene samples [ 22 ]. These groups emphasized the need to have future rapid DNA systems with (1) methods to identify low quantity, degradation, and inhibition as well as meeting the human quantification requirements shared by SWGDAM and others, (2) the ability to export analyzable raw data for analysis or reanalysis by trained and qualified forensic DNA analysts, (3) an on-board fully automated expert system to accurately flag single-source or mixture DNA profiles requiring analyst evaluation, (4) improved peak height ratio balance (per locus and across loci) for low-quality and mixture samples “through enhancements in extraction efficiencies, changes in cycling parameters, and/or changes in STR kit chemistries,” and (5) published developmental validation studies on a wide variety of forensic evidence type samples with “data-supported recommendations regarding types of forensic evidence that are suitable and unsuitable for use with Rapid DNA technology” [ 22 ].

With a likely increase in the capabilities and the availability of rapid DNA systems, investigators will need to decide whether to use this capability onsite in specific situations or to send collected samples to a conventional forensic laboratory for processing at a later time. A group in the Netherlands collaborated with the New York City Police Department Crime Scene Unit and Evidence Collection Team to explore a decision support system [ 60 ]. In this study, participants were informed that rapid DNA testing was less sensitive compared to laboratory analysis and that the sample would be consumed, but that results from rapid DNA testing could identify a suspect within 2 h as opposed to waiting an average of 45 days for the laboratory results [presumably due to sample backlogs]. They were also told that a DNA profile obtained with rapid DNA would be acceptable in court. In the end, “>90% of the participants (85 out of 91) saw added value for using a Rapid DNA device in their investigative process …” with “a systematic approach, which consists of weighing all possible outcomes before deciding to use a Rapid DNA analysis device” [ 60 ]. The authors note that for such an approach to be successful “knowledge on DNA success rates [with various evidence types] is necessary in making evidence-based decisions for Rapid DNA analysis” [ 60 ].

A group in Australia performed a cost-benefit analysis of a decentralized rapid DNA workflow that might exist in the future with instruments placed at police stations around their country [ 61 ]. A virtual assessment considered all reference DNA samples collected during a two-month time period at 10 participating police stations in five regions of Australia. Processing times at the corresponding DNA analysis laboratories were calculated based on when the sample was received compared to the day when a DNA profile was obtained for that sample. From the survey conducted, it was estimated that up to 80,000 reference DNA samples are currently processed each year in forensic DNA laboratories across Australia [ 61 ].

Consumable costs for conventional DNA testing reagents in Australia were found to range from $17 to $35 whereas the rapid DNA consumable costs were estimated to be $100 per sample along with an anticipated $100,000 instrument cost per police station. Of course, the rate of use is expected to vary based on the number of reference samples collected in that jurisdiction. Since rapid DNA instruments utilize consumable cartridges with expiration dates, it was estimated that a police station would need to process six DNA samples per week to avoid having to discard an expired cartridge and thus increase the overall cost of their rapid DNA testing efforts. The authors of this study conclude “that routine laboratory DNA analysis meets the current needs for the majority of cases … It is anticipated that while the cost discrepancy between laboratory and rapid DNA processing remains high, the uptake of the technology in Australia will be limited [at least for a police booking station scenario]” [ 61 ].

Rapid DNA technology can be used in a variety of contexts including some that extend beyond traditional law enforcement. Seven distinct use contexts for rapid DNA capabilities have been described [ 62 ]: (1) evidence processing at or near crime scenes to generate leads for confirmation by a forensic laboratory, (2) booking or detection stations to compare an individual's DNA profile to a forensic database while the individual is still in custody, (3) disaster victim identification to permit rapid DNA processing of a victim's family members during their visit to family assistance centers when filing missing persons reports, (4) missing persons investigations to quickly process unidentified human remains and/or family reference samples to generate leads for confirmation by a forensic laboratory, (5) border security to develop DNA data from detainees for comparison to indices of prior border crossers while the individual is still in custody, (6) human trafficking and immigration fraud detection to permit immigration officials to verify family relationship claims, and (7) migrant family reunification to allow immigration officials to verify parentage claims and reunite family members separated at the border. Social and ethical considerations have been proposed for each of these use contexts in terms of data collection, data access and storage, and oversight and data protection [ 62 ].

One study [ 47 ] evaluating buccal swabs and mock disaster victim identification samples drew an important conclusion worth repeating here: “The Rapid DNA system provides robust and automated analysis of forensic samples without human review. Sample analysis failure can happen by chance in both the Rapid DNA system and conventional laboratory STR testing. While re-injection of PCR product is easily possible in the conventional method, this is not an option with the Rapid DNA system. Accordingly, the Rapid DNA system is a suitable choice but should be limited to samples that can easily be collected again if necessary or to samples that are of sufficient amount for repeated analysis. Application of this system to valuable samples such as those related to casework need to be considered carefully before analysis.”

2.2. Using DNA databases to aid investigations (national databases, familial searching, investigative genetic genealogy, genetic privacy & ethical concerns, sexual assault kit testing)

Forensic DNA databases can aid investigations by demonstrating connections between crime scenes, linking a previously enrolled DNA profile from an arrestee or convicted offender to biological material recovered from a crime scene, or aiding identification of missing persons through association of remains with biological relatives. Establishment of these databases requires significant investments over time to enroll data from crime scenes and potential serial offenders or unidentified human remains and relatives of missing persons. This section explores issues around national DNA databases, familial searching, investigative genetic genealogy, and genetic privacy and ethical concerns.

A systematic review regarding the effectiveness of forensic DNA databases looked at 19 articles published between 1985 and 2018 and found most studies support the assumption that DNA databases are an effective tool for the police, society, and forensic scientists [ 63 ]. Recommendations have been proposed to make cross-border exchange of DNA data more transparent and accountable with the Prüm system that enables information sharing across the European Union [ 64 ]. An analysis of news articles discussing the use of DNA testing in family reunification with migrants separated at the U.S.-Mexico border has been performed [ 65 ], and a standalone humanitarian DNA identification database has been proposed [ 66 ]. Aspects of international DNA kinship matching were explored to aid missing persons investigations and disaster victim identification processes [ 67 ]. A business case was presented for expanded DNA indirect matching using additional genetic markers, such as Y-chromosome STRs, mitochondrial DNA, and X-chromosome STRs, to reveal previously undetected familial relationships [ 68 ].

Approaches to transnational exchange of DNA data include (1) creation of an international DNA database, (2) linked or networked national DNA databases, (3) request-based exchange of data, and (4) a combination of these [ 69 ]. For example, the INTERPOL DNA database 33 contains more than 247,000 profiles contributed by 84 member countries. The I-Familia global database assists with missing persons identification based on international DNA kinship matching. 34

2.2.1. National DNA databases

Since the United Kingdom launched the first national DNA database in 1995, national DNA databases continue to be added in many countries including Brazil [ 70 , 71 ], India [ 72 ], Pakistan [ 73 , 74 ], Portugal [ 75 ], and Serbia [ 76 ]. A survey of 15 Latin American countries found that 13 of them had some kind of DNA database [ 77 ]. The opinions of 210 prisoners and prison officials in three Spanish penitentiary centers were also collected regarding DNA databases [ 78 ].

The effectiveness of databases has been debated over the years. Seven key indicators were used in a 2019 examination of the effectiveness of the UK national DNA database. These indicators included (1) implementation cost – the financial input required to implement the database system, (2) crime-solving capability – the ability of the database to assist criminal justice officials in case resolution, (3) incapacitation effect – the ability of the database to reduce crime through the incapacitation of offenders, (4) deterrence effect – the preventative potential of the database through deterrence of individuals from committing crime, (5) privacy protection – protection of the privacy or civil liberty rights of individuals, (6) legitimacy – compliance of the databasing system to the principle of proportionality, and (7) implementation efficiency – the time and non-monetary resource required to implement the database system [ 79 ].

A follow-up article concluded: “Available evidence shows that while DNA analysis has contributed to successful investigations in many individual cases, its aggregate value to the resolution of all crime is low” [ 80 ]. The systematic review of 19 articles on DNA databases cited previously noted “the expansion of DNA databases would only have positive effects on detection and clearance if the offender were already included in the database” [ 63 ]. When previous offenders are not already in a law enforcement DNA database to provide a hit to a crime scene profile, efforts are increasingly turning to familial searching and investigative genetic genealogy as described in the following sections.

2.2.2. Familial DNA searching

Familial DNA searching (FDS) extends the traditional direct matching of STR profiles within law enforcement databases to search for potential close family relationships, such as a parent or sibling, of a profile in the database. 35 FDS typically uses Y-STR lineage testing to narrow the set of candidate possibilities along with other case information such as geographic details of the crime and age of the person(s) of interest. For example, FDS helped solve murder cases in Romania [ 81 ] and China [ 82 ] by locating the perpetrator through a relative in the DNA database. A survey of 103 crime laboratories in the United States found that 11 states use FDS while laboratories in 24 states use a similar but distinct practice of partial matching [ 83 ].

The expansion of the number of STRs from 15 to 20 or 21 helps distinguish between true and false matches during a DNA database search by reducing the number of FDS adventitious matches [ 84 ]. Another study noted that the choice of allele frequencies affects the rate at which non-relatives are erroneously classified as relatives and found that using ancestry inference on the query profile can reduce false positive rates [ 85 ]. New Y-STR kits have been developed to assist with familial searching [ 86 , 87 ]. FDS of law enforcement databases differs from investigative genetic genealogy in two important ways – the genetic markers and the databases used for searching [ 88 , 89 ].

2.2.3. Investigative genetic genealogy

In recent years when national DNA databases fail to generate a lead to a potential person of interest, law enforcement agencies have started to utilize the capabilities of investigative genetic genealogy (IGG), also called forensic genetic genealogy (FGG) or forensic investigative genetic genealogy (FIGG), as an approach to locate potential persons of interest in criminal or missing persons cases. For example, a pilot case study in Sweden used IGG to locate the perpetrator of a double murder from 2004 who had evaded detection despite 15 years of various investigation efforts including more than 9000 interrogations and mass DNA screenings of more than 6000 men [ 90 ]. Hardly a week goes by without mention in the global media of another cold case being solved with IGG. Since the arrest of Joseph DeAngelo in April 2018 identified as the infamous Golden State Killer using IGG, hundreds of cold criminal and unidentified human remains cases have been resolved [ 91 ].

IGG involves examination of about 600,000 single nucleotide polymorphisms (SNPs), rather than the 20 or so STRs used in conventional forensic DNA testing, to enable associations of relatives as distant as third or fourth cousins [ 17 ]. IGG relies on a combination of publicly accessible records and the consent of individuals who have uploaded their genetic genealogy DNA profiles to genetic genealogy databases [ 92 ]. Multiple reviews and research articles have been published describing current IGG methods, knowledge, and practice along with the effectiveness and operational limits of the technique [ 17 , 30 , [93] , [94] , [95] , [96] , [97] ]. IGG works best with high-quality, single-source DNA samples. A case study involving whole genome sequencing of human remains from a 2003 murder victim found that it was possible to perform IGG for identification of the victim in this situation [ 98 ].

The four main direct-to-consumer (DTC) genetic genealogy companies, 23andMe (Mountain View, CA), Ancestry (Salt Lake City, UT), FamilyTree DNA (Houston, TX), and My Heritage (Lehi, UT), have DNA data from over 41 million individuals 36 as of July 2022 [ 97 ]. Individuals can upload their DTC data to GEDmatch, which is a DNA comparison and analysis website launched in 2010 and purchased in 2019 by Verogen (San Diego, CA). Law enforcement IGG searches are currently permitted with DTC data for individuals who opt into the GEDmatch database or do not opt out of the FamilyTree DNA database [ 99 , 100 ]. Currently most DTC genetic genealogy data comes from the United States and individuals of European origin. A UK study found that 4 of 10 volunteer donors could be identified with IGG including someone of Indian heritage demonstrating that under the right circumstances individuals of non-European origin can be identified [ 101 ].

As noted previously in Section 1.2.1 , the U.S. Department of Justice released an interim policy guide to forensic genetic genealogical DNA analysis and searching [ 23 ], and the FBI Laboratory's chief biometric scientist published an editorial in Science calling for responsible genetic genealogy [ 24 ]. SWGDAM has provided an overview of IGG that emphasizes the approach being used only after a regular STR profile search of a law enforcement DNA database fails to produce any investigative leads [ 102 ]. Policy and practical implications of IGG have been explored in Australia [ 103 ] and within the UK as part of probing the perceptions of 45 professional and public stakeholders [ 104 , 105 ].

Four misconceptions about IGG were examined by several members of the SWGDAM group: (1) when law enforcement conducts IGG in a genetic genealogy database, they are given special access to participants' SNP profiles, (2) law enforcement will arrest a genetic genealogy database participant's relatives based on the genetic information the participant provided to the database, (3) IGG necessarily involves collecting and testing DNA samples from a larger number of innocent persons than would be the case if IGG were not used in the investigation, and (4) IGG is or soon will be ubiquitous because there are no barriers to IGG that limit the cases in which it can be conducted [ 106 ].

In May 2021, the state of Maryland passed the first law in the United States and in the world that regulates law enforcement's use of DTC genetic data to investigate crimes. A policy forum article in Science explained how this new law provides a model for others in this area [ 107 ]. Six important features were described: (1) requiring judicial authorization for the initiation of an IGG search, (2) affirming individual control over the investigative use of one's genetic data, (3) establishing strong protections for third parties who are not suspects in the case, (4) ensuring that IGG is available to prove either guilt or innocence, (5) imposing consequences and fines for violations, and (6) requiring annual public reporting and review to enable informed oversight of IGG methods. However, as of September 2022, these regulations have not been implemented apparently due to lack of resources with these unfunded requirements. 37

Efforts have been made to raise awareness among defense attorneys about how IGG searches can potentially invade people's privacy in unique ways [ 108 ]. Important perspectives on ethical, legal, and social issues have been offered along with directions for future research [ 109 ]. These concerns about data privacy, public trust, proficiency and agency trust, and accountability have led to a call for standards and certification of IGG to address issues raised by privacy scholars, law enforcement agencies, and traditional genealogists [ 110 , 111 ] and for an ethical and privacy assessment framework covering transparency, access criteria, quality assurance, and proportionality [ 112 ].

2.2.4. Genetic privacy and ethical concerns

Two important topics are considered in this section: (1) do the genetic markers used in traditional forensic DNA typing reveal more than identity and therefore potentially impact privacy of the individuals tested? and (2) are samples collected and tested according to ethical principles?

Forensic DNA databases utilize STR markers that were intentionally selected to avoid phenotypic associations. An extensive review of the literature examined 107 articles associating a forensic STR with some genetic trait and found “no demonstration of forensic STR variants directly causing or predicting disease” [ 113 ]. A study of the potential association of 15 STRs and 3 facial characteristics on 721 unrelated Han Chinese individuals also found “scarcely any association between [the] STRs with studied facial characteristics” [ 114 ].

In 2021, the American Type Culture Collection (ATCC) published a standard for authentication of human cell lines using DNA profiling with the 13 CODIS STR markers [ 115 ]. This use of forensic STR markers for biospecimen authentication led a bioethicist and a law professor to write a policy forum article in Science titled “Get law enforcement out of biospecimen authentication” [ 116 ]. The authors of this policy forum believe that using the same genetic markers could potentially: (1) undermine efforts to recruit research participants from historically marginalized and excluded groups that are underrepresented in research, (2) risk drawing law enforcement interest in gaining access to these research data, and (3) impose additional potential harms on already vulnerable populations, particularly children. Instead they advocate for using non-CODIS STRs or a new SNP assay to distinguish biospecimens in repositories, something done recently at the Coriell Institute for Medical Research with six new STR markers [ 117 ]. A responsive letter to the editor regarding this policy forum article expressed that “their proposal could potentially create artificial silos between genomic data in the justice system and in biomedical research, making it inefficient and ultimately counterproductive” [ 118 ]. The authors of the original article responded that “the risk of attracting law enforcement interest to research data increases when the data are available in a recognizable way” [ 119 ].

Modern scientific research seeks to protect the dignity, rights, and welfare of research participants by following ethical requirements. Six forensic science journals over the time period of 2010–2019 were examined for their reporting of ethical approval and informed consent in original research using human or animal subjects [ 120 ]. These journals were Forensic Science International: Genetics , Science & Justice , Journal of Forensic and Legal Medicine , the Australian Journal of Forensic Sciences , Forensic Science International , and the International Journal of Legal Medicine . A total of 3010 studies that described research on human or animal subjects and/or samples were selected from these journals with only 1079 articles (36%) reporting that they had obtained ethical approval and 527 articles (18%) stating that informed consent was sought either by written or verbal agreement. The authors of this study noted that reported compliance with ethical guidelines in forensic science research and publication was below what is considered minimal reporting rates in biomedical research and encouraged widespread adoption of the 2020 guidelines described below [ 120 ].

Guidelines and recommendations for ethnical research on genetics and genomics of biological material were jointly adopted and published in Forensic Science International: Genetics [ 121 ] and Forensic Science International: Reports [ 122 ]. These guidelines utilize the following principles as prerequisites for publication in these two journals as well as the Forensic Science International: Genetics Supplement Series : (1) general ethics principles that are regulated by national boards and represent widely signed international agreements, (2) universal declarations that require implementations in state members, such as the World Medical Association Declaration of Helsinki biomedical research on human subjects, and (3) universal declarations and principles drafted by independent organizations that have been widely adopted by the scientific community. This includes the U.S. Federal Policy for the Protection of Human Subjects (“Common Rule”) that was revised in 2017 (with a compliance date delayed to January 21, 2019). 38

Submitted manuscripts must provide the following supporting documentation to demonstrate compliance with the publication guidelines: (1) ethical approval in the country of [sample] collection by the appropriate local ethical committee or institutional review board, (2) ethical approval in the country of experimental work according to local legislation; if material collection and experimentation are conducted in different countries, both (1) and (2) are required, (3) template of consent forms in the case of human material as approved by the relevant ethical committee, and (4) approved export/import permits as applicable. Authors must declare in their submitted manuscript that these guidelines have been strictly followed [ 121 , 122 ].

Forensic genetic frequency databases, such as the Y-chromosome Haplotype Reference Database (YHRD), have been challenged over the ethics of DNA holdings, specifically of samples originating from the minority Muslim Uyghur population in western China [ 123 , 124 ]. A survey of U.S. state policies on potential law enforcement access to newborn screening samples found that nearly one-third of states permit these samples or their related data to be disclosed to or used by law enforcement and more than 25% of states have no discernible policy in place regarding law enforcement access [ 125 ].

A framework for ethical conduct of forensic scientists as “lived practice” has been proposed, and three case studies were discussed in terms of decision-making processes involving forensic DNA phenotyping and biographical ancestry testing, investigative genetic genealogy, and forensic epigenetics [ 126 ]. An ethos for forensic genetics involving the values of integrity, trustworthiness, and effectiveness has likewise been described [ 127 ].

2.2.5. Sexual assault kit testing

Unsubmitted or untested sexual assault kits (SAKs) may exist in police or laboratory evidence lockers for many years leading to rape kit backlogs that can spark community outrage when discovered. A number of articles have been published in the past three years describing success rates with examining SAKs and the policies surrounding them. For example, an evaluation of 3422 unsubmitted SAKs in Michigan found 1239 that produced a DNA profile eligible for upload into CODIS with 585 yielding a CODIS hit [ 128 ]. In addition, results from a groping and sexual assault case were presented to support the expansion of touch DNA evidence in these types of cases [ 129 ].

To assess success rates in their jurisdiction, the Houston Police Department randomly selected 491 cases of over 6500 previously unsubmitted sexual assault kits [ 130 ]. Of these, 336 cases (68%; 336/491) screened positive for biological evidence; a DNA profile was developed in 270 cases (55%; 270/491) with 213 (43%; 213/491) uploaded to CODIS; and 104 (21% total; 104/491 or 49% of uploaded profiles; 104/213) resulted in a CODIS hit. The statute of limitation had expired in 44% of these CODIS-hit cases, which prohibited arrests and prosecution. Victims were unwilling to participate in a follow-up investigation in another 25% of these cases. When the data were compiled for the publication, charges had been filed in only one CODIS-hit case [ 130 ].

Sexual assault cases can be difficult to prosecute as victims may be re-traumatized when a cold case is reopened. The authors of one study shared: “A key to successful pursuit of cold case sexual assaults is to have a well-crafted victim-notification plan and a victim advocate as part of the investigative team” [ 131 ]. Interviews with eight assistant district attorneys provided important prosecutors’ perspectives on SAK cases, the development of narratives to explain the evidence in a case, and the decision on whether a case should be pursued or what further investigative activities may be needed [ 132 ]. The authors concluded: “Our findings suggest that forensic evidence does not magically lead to criminal justice outcomes by itself, but must be used thoughtfully in conjunction with other evidence as part of a well-considered strategy of investigation and prosecution” [ 132 ].

Discussing a data set from Denver, Colorado where 1200 sexual assault cold cases with testable DNA samples were examined and 600 cases were processed through the laboratory resulting in 97 CODIS hits, 55 arrests and court filings, and 48 convictions, the authors conclude that the cost of the Denver cold case sexual assault program was worth the investment [ 131 ].

From December 2015 to July 2018, the Palm Beach County Sheriff's Office (Florida, USA) researched more than 5500 cases and evaluated evidence from previously untested sexual assault kits spanning a 43-year period at a cost of over $1 million. Of the 1558 sexual assaults examined, there were 686 cases (44%; 686/1558) with CODIS-eligible profiles, 261 CODIS hits, and 5 arrests when the article was written in mid-2019 [ 133 ]. The Palm Beach County Sheriff's Office also helped develop a backlog reduction effort through creating a biological processing laboratory within the Boca Raton Police Services Department [ 134 ]. With this joint effort from 2016 to 2018, the total average turnaround time decreased from 30 days to under 20 days with the 3489 DNA profiles entered into CODIS resulting in 1254 associations and 965 investigations aided. Important takeaway lessons include the value of (1) engaging legal counsel early to outline necessary legal procedures and the timeline, (2) bringing all stakeholders “to the table” early to discuss expectations, as well as legal and operational responsibilities, and (3) creating a realistic timeline with a comprehensive memorandum of understanding so all parties have agreed to their roles and responsibilities [ 134 ].

From 275 previously untested sexual assault kits submitted for DNA testing in one region of Central Brazil, a total of 176 profiles were uploaded to their DNA database resulting in 60 matches (34%; 60/176) and 32 assisted investigations (18%; 32/176) with information about the suspect identity or the connection of serial sexual assaults assigned to the same individual [ 135 ]. Another study from the same region of Brazil examined 2165 cases and noted that 13% (286/2165) had information regarding the victim-offender relationship with 63% (179/286) being stranger-perpetrated rapes and 37% (107/286) being non-stranger [ 136 ]. The authors then summarize: “Hits were detected only with stranger-perpetrated assaults ( n  = 41), which reinforces that DNA databases are fundamental to investigate sexual crimes. Without DNA typing and DNA databases, probably these cases would never be solved” [ 136 ].

Given that laboratories have limited resources and need to prioritize their efforts, some business analytics have been applied to SAK testing. An analysis of the potential societal return on investment (ROI) for processing backlogged, untested SAKs reported a range of 10%–65% ROI depending on the volume of activity for the laboratory conducting the analysis [ 137 ]. An evaluation of data from 868 SAKs tested by the San Francisco Policy Department Criminalistics Laboratory during 2017–2019 found that machine learning algorithms outperformed forensic examiners in flagging potentially probative samples [ 138 ].

An examination of 5165 SAKs collected in Cuyahoga County (Ohio, USA) from 1993 through 2011 found 3099 with DNA of which 2127 produced a CODIS hit, with 803 investigations leading to an indictment and eventually 78 to trial along with 330 pleas [ 139 ]. The authors report a “cost savings to the community of $26.48 million after the inclusion of tangible and intangible costs of future sexual assaults averted through convictions” and advocate for “the cost-effectiveness of investigating no CODIS hit cases and support an ‘investigate all’ approach” [ 139 ]. Likewise an assessment of 900 previously-untested SAKs from Detroit (Michigan, USA) found that “few of the tested variables were significant predictors of CODIS hit rate” and “testing all previously-unsubmitted kits may generate information that is useful to the criminal justice system, while also potentially addressing the institutional betrayal victims experienced when their kits were ignored” [ 140 ].

A group in the Philippines described an integrated system to improve their SAK processing [ 141 ]. With an optimized workflow in Montreal, Canada, SAK processing median turnaround time decreased from 140 days to 45 days with a foreign DNA profile being obtained in 44% of cases [ 142 ]. In addition, this group examined casework data to guide resource allocation through identifying the likelihood of specific types of cases and samples yielding foreign biological material [ 142 ]. Decision trees and logistic regression models were also used to try and predict whether or not SAKs will yield a CODIS-eligible DNA profile [ 143 ]. Finally, direct PCR and rapid DNA approaches to streamline SAK testing were reviewed [ 144 ].

2.3. Forensic biology and body fluid identification

The basic workflow for biological samples in forensic examinations typically involves a visual examination of the evidence, a presumptive and/or confirmatory test for a suspected body fluid (e.g., the amylase assay for saliva), and DNA analysis and interpretation [ 145 ]. Body fluid identification (BFID), in particular with blood, saliva, semen, or vaginal fluid stains, provides valuable evidence in many investigations that can aid in the resolution of a crime [ 146 ]. Many of these BFID tests are presumptive and not nearly as sensitive as modern DNA tests meaning that “obtaining a DNA profile without being able to associate [it] with a body fluid is an increasingly regular occurrence” and “it is necessary and important, especially in the eyes of the law, to be able to say which body fluid that the DNA profile was obtained from” [ 147 ].

A number of approaches are being taken to improve the sensitivity and specificity of BFID in recent years including DNA methylation [ [148] , [149] , [150] , [151] , [152] , [153] , [154] , [155] , [156] , [157] , [158] , [159] , [160] , [161] ], messenger RNA (mRNA) [ [162] , [163] , [164] , [165] , [166] ], microRNA (miRNA) [ 167 ], protein mass spectrometry for seminal fluid detection [ 168 ], and microbiome analysis [ 169 , 170 ]. Although many new techniques are being described in the scientific literature, traditional methods for semen identification are still widely used in regular forensic casework [ 171 ].

When using RNA assays, DNA and RNA are co-extracted from examined samples [ 172 , 173 ]. Some tests may only distinguish between two possible body fluids, such as saliva and vaginal fluid [ 174 ], while other tests may attempt to distinguish six forensically relevant body fluids – vaginal fluid, seminal fluids, sperm cells, saliva, menstrual blood, and peripheral blood – although not always as clearly as desired [ 175 ]. BFID assays must also cope with mixed body fluids [ 176 ].

2.4. DNA collection and extraction

The process of obtaining a DNA profile begins with collecting a biological sample and extracting DNA from it. A review of recent trends and developments in forensic DNA extraction focused on isolating male DNA in sexual assault cases, using portable rapid DNA testing instruments, recovering DNA from difficult samples such as human remains, and bypassing DNA extraction altogether with direct PCR methods [ 177 ].

2.4.1. Touch evidence and fingerprint processing methods

Various studies have explored the compatibility of common fingerprint processing methods with DNA typing results [ [178] , [179] , [180] , [181] , [182] , [183] , [184] , [185] , [186] , [187] , [188] ]. For example, DNA recovery was explored after various steps in three different latent fingerprint processing methods – and fewer treatments were judged preferable with a 1,2-indanedione-zinc (IND/Zn) method appearing least harmful to downstream DNA analysis [ 187 ]. A different study found improved recovery of DNA from cigarette butts following latent fingerprint processing with 1,8-diazafluoren-9-one (DFO) compared to IND/Zn [ 179 ].

DNA losses were quantified with mock fingerprints deposited on four different surfaces to better understand DNA collection and extraction method performance [ 189 ]. The application of Diamond Dye has been shown to enable visualization of cells deposited on surfaces without interfering with subsequent PCR amplification and DNA typing [ [190] , [191] , [192] ].

It was possible to recover DNA profiles from clothing that someone touched for as little as 2 s [ 193 ]. DNA sampling success rates from car seats and steering wheels were studied [ 194 ] and recovery of DNA from vehicle surfaces using different swabs was explored [ 195 ]. In addition, the double-swab technique, where a wipe using a wet swab is followed by a wipe with a dry one, was revisited with an observation that for non-absorbing surfaces, the first web swab yielded 16 times more DNA than the second dry swab [ 196 ]. Swabs of cotton, flocked nylon, and foam reportedly provided equivalent DNA recoveries for smooth/non-absorbing surfaces, and an optimized swabbing technique involving the application of a 60-degree angle and rotating the swab during sampling improved DNA yields for cotton swabs [ 197 ].

2.4.2. Results from unfired and fired cartridge cases

Ammunition needs to be handled to load a weapon and thus DNA from the handler may be deposited onto the ammunition via touch [ 198 ]. Important progress has been made in recovering DNA from ammunition such as unfired cartridges or fired cartridge cases (FCCs) that may remain at a crime scene after a weapon has been fired. Trace quantities of DNA recovered from firearm or FCC surfaces has been used to try and link results to gun-related crimes.

A 2019 review of the literature regarding obtaining successful DNA results from ammunition examined collection techniques, extraction methodologies, and various amplification kits and conditions [ 199 ]. A direct PCR approach detected more STR alleles than methods using DNA extraction, and the authors noted that mixtures are commonly observed from gun surfaces, bullets, and cartridges in both controlled experimental conditions and from actual casework evidence and they encourage careful interpretation of these results [ 200 ]. The development of a crime scene FCC collector was combined with a new DNA recovery method that uses a rinse-and-swab technique [ 201 ].

Research studies and review articles have considered factors affecting DNA recovery from cartridge cases and the impact of metal surfaces on DNA recovery [ [202] , [203] , [204] , [205] , [206] , [207] , [208] , [209] ]. Recovery of mtDNA from unfired ammunition components has been assessed for sequence quality [ 210 ].

2.5. DNA typing

Following collection of DNA evidence and its extraction from biological samples, the typical typing process involves DNA quantitation, PCR amplification of STR markers, and STR typing using capillary electrophoresis. Direct PCR avoids the DNA extraction and quantitation steps, which can improve recovery of trace amounts of DNA [ 211 , 212 ]. Whole genome amplification prior to STR analysis has also been examined to aid recovery of degraded DNA [ 213 ] and to enable profiling of single sperm cells [ 214 ].

PCR amplification using STR typing kits can sometimes produce artifacts that impact DNA interpretation including missing (null) alleles [ 215 ], false tri-allelic patterns [ 216 ] or extra peaks when amplified in the presence of microbial DNA [ [217] , [218] , [219] ].

Applied Biosystems Genetic Analyzers have been the primary means of performing multi-colored capillary electrophoresis for many years [ 4 ]. First experiences with Promega's new Spectrum Compact CE System have recently been reported [ 220 ]. A number of new research and commercial STR kits have been introduced in recent years along with the publication of at least 24 validation studies ( Table 5 ). These validation studies typically follow guidelines outlined by the ENFSI DNA Working Group, 39 SWGDAM 40 , or a 2009 Chinese National Standard. 41

STR kits assessed with 24 published validation studies during 2019–2022.

A report on the first two years of submissions to the STRidER 42 (STRs for Identity ENFSI Reference) database for online allele frequencies revealed that 96% of the submitted 165 autosomal STR datasets generated by CE contained errors, showing the value of centralized quality control and data curation [ 245 ].

2.6. DNA interpretation at the source or sub-source level

The designation of STR alleles and genotypes of contributors in DNA mixtures are key aspects of DNA interpretation [ 246 , 247 ]. Electropherograms generated by CE instruments exhibit both STR alleles and artifacts that complicate data interpretation. Efforts are underway to understand and model instrumental artifacts [ [248] , [249] , [250] , [251] ] as well as biological artifacts of the PCR amplification process such as STR stutter products [ 252 , 253 ]. Machine learning approaches are being applied to classify artifacts versus alleles with the goal to eventually replace manual data interpretation with computer algorithms [ [254] , [255] , [256] , [257] ]. One such program, FaSTR DNA, enables potential artifact peaks from stutter, pull-up, and spikes to be filtered or flagged, and a developmental validation has been published examining 3403 profiles generated with seven different STR kits [ 258 ].

2.6.1. DNA mixture interpretation

Forensic evidence routinely contains contributions from multiple donors, which result in DNA mixtures. A number of approaches have been taken and advances made in DNA mixture interpretation [ 259 ]. These include probabilistic genotyping software [ 15 ], using genetic markers beyond traditional autosomal STR typing [ 260 ], or separating contributor cells and performing single-cell analysis [ [261] , [262] , [263] , [264] , [265] , [266] ].

In June 2021, the National Institute of Standards and Technology (NIST) released a draft report regarding the scientific foundations of DNA mixture interpretation [ 267 ]. This 250-page document described 16 principles that underpin DNA mixture interpretation, provided 25 key takeaways, and cited 528 references. NIST also began a Human Factors Expert Working Group on DNA Interpretation in February 2020 and plans to release a report with recommendations in 2023.

Assessment of the number of contributors (NoC) is a critical element of accurate DNA mixture interpretation. For example, the LRs relating to minor contributors can be reduced when the incorrect number of contributors is assumed [ 268 ]. Allele sharing among contributors to a mixture and masking of alleles due to STR stutter artifacts can lead to inaccurate NoC estimates based on simply counting the number of alleles at a locus. Different approaches and software programs have been used for NoC estimation [ [269] , [270] , [271] , [272] , [273] , [274] , [275] ]. Total allele count (TAC) distribution via TAC curves showed an improvement in manually estimating the number of contributors with complex mixtures [ 276 ]. Sequence analysis of STR loci expands the number of possible alleles compared to CE-based length measurements and thus can improve NoC estimates [ 277 ].

In the past three years, validation studies have been performed with a number of probabilistic genotyping software (PGS) systems including EuroForMix [ 278 ], DNAStatistX [ 279 , 280 ], TrueAllele [ 281 ], STRmix [ 282 ], Statistefix [ 283 ], Mixture Solution [ 284 ], Kongoh [ 285 ], and MaSTR [ 286 , 287 ]. Developers of EuroForMix, DNAStatistX, and STRmix provided a review of these systems [ 288 ]. Multi-laboratory assessments have been described [ 289 , 290 ] and likelihood ratios obtained from EuroForMix and STRmix compared [ [291] , [292] , [293] , [294] ]. With a growing literature in this area, there are many other articles that could have been cited.

2.7. DNA interpretation at the activity level

DNA interpretation at the source or sub-source level helps to answer the question of who deposited the cell material, whether attribution for the result can be made to a specific cell type (i.e., source level) or simply to the DNA if no attribution can be made to a specific cell type (i.e., sub-source level). Activity-level propositions seek to answer the question of how did an individual's cell material get there. Interpretation at the activity level is sometimes referred to as evaluative reporting [ 295 , 296 ].

In 2020, the ISFG DNA Commission [ 38 ] discussed the why, when, and how to carry out evaluative reporting given activity level propositions through providing examples of formulating these propositions. These Commission recommendations emphasize that reports using a likelihood ratio based on case-specific propositions and relevant conditioning information should highlight the assumptions being made and that “it is not valid to carry over a likelihood ratio from a low level, such as sub-source, to a higher level such as source or activity propositions … because the LRs given sub-source level propositions are often very high and LRs given activity level propositions will often be many orders of magnitude lower” [ 38 ]. Another recommendation specifies that “scientists must not give their opinion on what is the ‘most likely way of transfer’ (direct or indirect), as this would amount to giving an opinion on the activities and result in a prosecutor's fallacy (i.e., give the probability that X is true). The scientists' role is to assess the value of the results if each proposition is true in accordance with the likelihood ratio framework (the probability of the results if X is true and if Y is true)” [ 38 ] (emphasis in the original). This DNA Commission provided 11 recommendations and 4 considerations that should be studied carefully by those who implement activity-level DNA interpretation.

2.7.1. DNA transfer and persistence studies

To evaluate DNA findings given activity-level propositions it is important to understand the factors and variables that may impact DNA transfer, persistence, prevalence, and recovery (DNA-TPPR). These factors include history of contacting surfaces, biological material type, quantity and quality of DNA, dryness of biological material, manner and duration of contact, number and order of contacts, substrate type(s), time lapses and environment, and methods and thresholds used in the forensic DNA laboratory to generate the available data [ 297 ].

Three valuable review articles were published on this topic in 2019 [ 14 , 28 , 299 ]. Following a comprehensive January 2019 review that cited [ 298 ] references on DNA-TPPR [ 14 ], the same authors provided an update in November 2021 on recent progress towards meeting challenges and a synopsis of 144 relevant articles published between January 2018 and March 2021 [ 297 ]. While few studies provide the information needed to help assign probabilities of obtaining DNA results given specific sets of circumstances, progress includes use of Bayesian Networks [ 300 ] to identify variables for complex transfer scenarios [ 38 , [301] , [302] , [303] , [304] , [305] ] as well as development of an online database DNA-TrAC 43 for relevant research articles [ 299 ] and a structured knowledge base 44 with information to help practitioners interpret general transfer events at an activity level [ 306 ].

Forensic DNA pioneer Peter Gill emphasized that awareness of the limitations of DNA evidence is important for users of this data given that an increased sensitivity of modern DNA methods means that DNA may be recovered that is irrelevant to the crime under investigation [ 307 ]. An ISFG DNA Commission (see Section 1.2.5 ) emphasized that the strength of evidence associated with a DNA match at the sub-source level cannot be carried over to activity level propositions [ 38 ]. Structuring case details into propositions, assumptions, and undisputed case information has been encouraged [ 308 ].

Factors affecting variability of DNA recovery on firearms were studied with four realistic, casework-relevant handling scenarios along with results obtained including DNA quantities, number of contributors, and relative profile contributions for known and unknown contributors [ 309 ]. These studies found that sampling several smaller surfaces on a firearm and including the sampling location in the evaluation process can be helpful in assessing results given alternative activity-level propositions in gun-related crimes. The authors recommend that “further extensive, detailed and systematic DNA transfer studies are needed to acquire the knowledge required for reliable activity-level evaluations” [ 309 ].

Other recent studies on DNA-TPPR include examining prevalence and persistence of DNA or saliva from car drivers and passengers [ [310] , [311] , [312] ], evaluation of DNA from regularly-used knives after a brief use by someone else [ 313 ], studying the accumulation of endogenous and exogenous DNA on hands [ 314 ] and non-self-DNA on the neck [ 315 ], considering the potential of DNA transfer via work gloves [ 316 , 317 ] or during lock picking [ 318 ], and investigating whether DNA can be recovered from illicit drug capsules [ 319 , 320 ] or packaging [ 321 ] to identify those individuals preparing or handling the drugs.

Efforts have been made to estimate the quantity of DNA transferred in primary versus secondary transfer scenarios [ 322 ]. As quantities of DNA transferred can be highly variable and thought to be dependent on the so-called “shedder status” – how much DNA an individual exudes, several studies explored this topic [ [323] , [324] , [325] , [326] , [327] ]. Studies have also considered the level of DNA an individual transfers to untouched items in their immediate surroundings [ 328 ], the position and level of DNA transferred during digital sexual assault [ 329 ] or during various activities with worn upper garments [ 330 , 331 ], and the DNA composition on the surface of evidence bags pre- and post-exhibit examination [ 332 ]. Studies assessing background levels of male DNA on underpants worn by females [ 333 ] and background levels of DNA on flooring within houses [ 334 ] are providing important knowledge about the possibilities and probabilities of DNA transfer and persistence.

The authors of one study summarize some key points that could be extended to many other studies as words of caution: “From a wider trace DNA point of view, this study has demonstrated that the person who most recently handled an item may not be the major contributor and someone who handled an item for longer may still not be the major contributor if they remove more DNA than they deposit. The amount of DNA transferred and retained on an item is highly variable between individuals and even within the same individual between replicates” [ 320 ].

3. Emerging technologies, research studies, and other topics

New technologies to aid forensic DNA typing are constantly under development. This section explores recent activities with next-generation DNA sequencing, DNA phenotyping for estimating a sample donor's age, ancestry, and appearance, lineage markers, other markers and approaches, and non-human DNA and wildlife forensics, and is expected to be of value to researchers and those practitioners looking to future directions in the field.

3.1. Next-generation sequencing

Next-generation sequencing (NGS), also known as massively parallel sequencing (MPS) in the forensic DNA community, expands the measurement capabilities and information content of a DNA sample beyond the traditional length-based results with STR markers obtained with capillary electrophoresis (CE) methods. Additional genetic markers, such as single nucleotide polymorphisms (SNPs), microhaplotypes, and mitochondrial genome (mtGenome) sequence, may be analyzed along with the full sequence of STR alleles. This higher information content per sample opens up new potential applications such as phenotyping of externally visible characteristics and biogeographical ancestry as described in review articles [ 335 , 336 ].

As mentioned in Section 1.2.1 , the NIJ Forensic Laboratory Needs Technology Working Group (FLN-TWG) published a 29-page implementation strategy on next-generation sequencing for DNA analysis in September 2021 [ 28 ]. This guide discusses how NGS works and its advantages and disadvantages, the various instrument platforms and commercial kits available with approximate costs, items to consider regarding facilities, data storage, and personnel training, and resources for implementing NGS technology. A total of 73% of 105 forensic DNA laboratories surveyed from 32 European countries already own an MPS platform or plan to acquire one in the next year or two and one-third of the survey participants already conduct MPS-based STR sequencing, identity, or ancestry SNP typing [ 337 ].

Validation studies have been described with the ForenSeq DNA Signature Prep kit and the MiSeq FGx system [ [338] , [339] , [340] ], with the Verogen ForenSeq Primer Mix B for phenotyping and biogeographical ancestry predictions [ 341 , 342 ], and for resizing reaction volumes with the ForenSeq DNA Signature Prep kit library preparation [ 343 ]. MPS sequence data showed excellent allele concordance with CE results for 31 autosomal STRs in the Precision ID GlobalFiler NGS STR Panel from 496 Spanish individuals [ 344 ] and from 22 autosomal STR loci in the PowerSeq 46GY panel with 247 Austrians [ 345 ].

STR flanking region sequence variation has been explored [ 346 ] and reports of population data and sequence variation were published for samples from India [ 347 ], France [ 348 ], China [ 349 , 350 ], Korea [ 351 ], Brazil [ 352 ], Tibet [ 353 ], and the United States [ 354 ].

In April 2019 the STRAND ( S hort T andem R epeat: A lign, N ame, D efine) Working Group was formalized [ 355 ] to consider several possible approaches to sequence-based STR nomenclature that have been proposed [ 356 , 357 ]. An overview of software options has been provided for analysis of forensic sequencing data [ 358 ]. Some recent published options include STRinNGS [ 359 ], STRait Razor [ 360 ], ArmedXpert tools MixtureAce and Mixture Interpretation to analyze MPS-STR data [ 361 ], and STRsearch for targeted profiling of STRs in MPS data [ 362 ]. To aid interpretation of MPS-STR data, sensitivity studies were performed with single-source samples and sequence data analyzed by DNA quantity and method used [ 363 ]. A procedure has been described to address calculation of match probabilities when results are generated using MPS kits with different trim sites than those present in the relevant population frequency database [ 364 ]. Performance of different MPS kits, markers, or methods can be compared for accuracy and precision using the Levenshtein distance metric [ 365 ].

Novel MPS STR and SNP panels developed in recent years include IdPrism [ 366 ], a QIAGEN 140-locus SNP panel [ 367 ], the 21plex monSTR identity panel [ 368 ], a 42plex STR NGS panel to assist with kinship analysis [ 369 ], the 5422 marker FORCE (FORensic Capture Enrichment) panel [ 370 ], a forensic panel with 186 SNPs and 123 STRs [ 371 ], the SifaMPS panel for targeting 87 STRs and 294 SNPs [ 372 ], a 1245 SNP panel [ 373 ], 90 STRs and 100 SNPs for application with kinship cases [ 374 ], an adaption of the SNPforID 52plex panel to MPS [ 375 ], 448plex SNP panel [ 376 ], a 133plex panel with 52 autosomal and 81 Y-chromosome STRs [ 377 ], and a forensic identification multiplex with 1270 tri-allelic SNPs involving 1241 autosomal and 29 X-chromosome markers [ 378 ]. The 124 SNPs in the Precision ID Identity Panel were examined in a central Indian population [ 379 ] and human leukocyte antigen (HLA) alleles used in the early 1990s were revisited with MPS capability [ [380] , [381] , [382] ].

MPS methods have demonstrated utility with compromised samples [ [383] , [384] , [385] , [386] , [387] , [388] ] and mixture interpretation [ [389] , [390] , [391] , [392] , [393] , [394] , [395] ]. Microhaplotype assays have also been developed to assist with DNA mixture deconvolution [ 396 , 397 ]. Collaborative studies have explored variability with laboratory performance using MPS methods [ 398 , 399 ]. Population structure [ 400 ] and linkage and linkage disequilibrium [ 401 ] were examined among the markers in forensic MPS panels.

A review of transcriptome analysis using MPS discussed efforts with body fluid and tissue identification, determination of the time since deposition of stains and the age of donors, the estimation of post-mortem interval, and assistance to post-mortem death investigations [ 402 ]. The potential for MPS methods to assist with environmental trace analysis was reviewed in terms of forensic soil analysis, forensic botany, and human identification utilizing the skin microbiome [ 403 ]. The possibility of non-invasive prenatal paternity testing using cell-free fetal DNA from maternal plasma was explored with the Precision ID Identity Panel [ 404 ] and the ForenSeq DNA Signature Prep Kit [ 405 ]. Pairwise kinship analysis was also examined using the ForenSeq DNA Signature Prep Kit and multi-generational family pedigrees [ 406 , 407 ]. Nanopore sequencing has also been explored for sequencing STR and SNP markers [ [408] , [409] , [410] , [411] , [412] , [413] , [414] , [415] , [416] ].

3.2. DNA phenotyping (ancestry, appearance, age)

Continuing research into the genetic components of biogeographic ancestry, appearance, and age predictions have improved forensic DNA phenotyping capabilities [ 417 ]. These forensic innovations may sometimes impact public expectations [ 418 ]. The investigation in a murder case was assisted using information from forensic DNA phenotyping that predicted eye, hair, and skin color of an unknown suspect with the HIrisPlex-S system involving targeted massively parallel sequencing [ 419 ].

The VISAGE ( Vis ible A ttributes Through Ge nomics) Consortium, which consists of 13 partners from academic, police, and justice institutions in 8 European countries, has established new scientific knowledge and developed and tested prototype tools for DNA analysis and statistical interpretation as well as conducted education for stakeholders. In the 2019 to 2022 time window of this review, this concerted effort produced 45 one review article [ 417 ], 22 original research publications [ 337 , [420] , [421] , [422] , [423] , [424] , [425] , [426] , [427] , [428] , [429] , [430] , [431] , [432] , [433] , [434] , [435] , [436] , [437] , [438] , [439] , [440] ], and three reports [ [441] , [442] , [443] ].

DNA phenotyping is currently an active area of research, and numerous activities and publications exist beyond the VISAGE articles noted here. Another 137 articles have appeared in the literature in the past three years on biogeographical ancestry, appearance (primarily hair color, eye color, and skin color), and biological age predictions (typically utilizing DNA methylation) (see Supplemental File ).

3.3. Lineage markers (Y-chromosome, mtDNA, X-chromosome)

Lineage markers consist of Y-chromosome, mitochondrial DNA, and X-chromosome genetic information that may be inherited from just one parent without the regular recombination that occurs with autosomal DNA markers. Research in terms of new markers, assays, and population studies continue to be published for these lineage markers.

3.3.1. Y-chromosome

Several recent review articles were published on forensic applications of Y-chromosome testing [ [444] , [445] , [446] ]. As discussed previously in Section 1.2 , an ISFG DNA Commission summarized the state of the field with Y-STR interpretation [ 39 ]. Rapidly mutating Y-STR loci can be used to differentiate closely related males [ [447] , [448] , [449] ]. New statistical approaches to assessing evidence with Y-chromosome information have been described [ 450 , 451 ]. Four commercial Y-STR multiplexes were compared with the NIST 1032 U S. population sample set and the allele and haplotype diversities explored with length-based versus sequence-based information [ 452 ].

A number of Y-STR typing systems have been described along with validation studies, such as a 36plex [ 453 ], a 41plex [ 454 ], a 29plex [ 455 ], a 17plex [ 456 ], a 24plex [ 457 ], the Microreader 40Y ID System [ 458 ], the 24 Y-STRs in the AGCU Y SUPP STR kit [ 459 ], the DNATyper Y26 PCR amplification kit [ 460 ], a multiplex with 12 multicopy Y-STR loci [ 461 ], the Yfiler Platinum PCR Amplification Kit [ 462 ], a 45plex [ 463 ], the Microreader 29Y Prime ID system [ 464 ], an assay with 30 slow and moderate mutation Y-STR markers [ 465 ], the 17plex Microreader RM-Y ID System [ 466 ], and a 26plex for rapidly mutating Y-STRs [ 467 ]. A machine learning program predicted Y haplogroups using two Y-STR multiplexes with 32 Y-STRs [ 468 ].

Deletions and duplications with 42 Y-STR were reported in a sample of 1420 unrelated males and 1160 father-son pairs from a Chinese Han population [ 469 ]. Using Y-STR allele sequences has enabled locating parallel mutations in deep-rooting family pedigrees [ 470 ]. The surname match frequency with Y-chromosome haplotypes was explored using 2401 males genotyped for 46 Y-STRs and 183 Y-SNPs [ 471 ]. In the Y-chromosome's role as a valuable kinship indicator to assist in genetic genealogy and forensic research, models to improve prediction of the time to the most recent common paternal ancestor have been studied with 46 Y-STRs and 1120 biologically related genealogical pairs [ 472 ]. A massively parallel sequencing tool was developed to analyze 859 Y-SNPs to infer 640 Y haplogroups [ 473 ]. Another MPS tool, the CSYseq panel, targeted 15,611 Y-SNPs to categorize 1443 Y-sub-haplogroup lineages worldwide along with 202 Y-STRs including 81 slow, 68 moderate, 27 fast, and 26 rapidly mutating Y-STRs to individualize close paternal relatives [ 474 ].

3.3.2. Mitochondrial DNA

Mitochondrial DNA (mtDNA), which is maternally inherited with a high copy number per cell, can aid human identification, missing persons investigations, and challenging forensic specimens containing low quantities of nuclear DNA such as hair shafts [ [475] , [476] , [477] ]. Validation studies have been published using traditional Sanger sequencing [ 478 ] and next-generation sequencing [ [479] , [480] , [481] ]. Illumina and Thermo Fisher now provide mtDNA whole genome NGS assays [ [482] , [483] , [484] , [485] ]. Many mtDNA population data sets were published in the past three years including high-quality data from U.S. populations [ 486 ]. The suitability of current mtDNA interpretation guidelines for whole mtDNA genome (mtGenome) comparisons has been evaluated [ 487 ].

NGS methods have increased sensitivity of mtDNA heteroplasmy detection [ 488 , 489 ], which can influence the ability to connect buccal reference samples and rootless hairs from the same individual [ 490 , 491 ]. Twelve polymerases were compared in terms of mtDNA amplification yields from challenging hairs – with KAPA HiFi HotStart and PrimeSTR HS outperforming AmpliTaq Gold DNA polymerase that is widely used in forensic laboratories [ 492 ]. Multiple studies and review articles have discussed distinguishing mtDNA from nuclear DNA elements of mtDNA (NUMTs) that have been inserted into our nuclear DNA [ [493] , [494] , [495] , [496] ].

NGS sequencing of the mtGenome has permitted improved resolution of the most common West Eurasian mtDNA control region haplotype [ 497 ]. Phylogenetic alignment and haplogroup classification have continued to be refined with new sequence information [ 498 ], and new assays have been developed to aid haplogroup classification [ 499 ]. Concerns over potential paternal inheritance of mtDNA have also been addressed [ 500 , 501 ].

3.3.3. X-chromosome

A 20-year review of X-chromosome use in forensic genetics examined the number and types of markers available, an overview of worldwide population data, the use of X-chromosome markers in complex kinship testing, mutation studies, current weaknesses, and future prospects [ 502 ]. One example of the forensic application of X-chromosome markers include use in relationship testing cases involving suspicion of incest or paternity without a maternal sample for comparison [ 503 ]. Four new X-STR multiplex assays were described along with validation studies including a 19plex [ 504 ], a 16plex [ 505 ], another 19plex – the Microreader 19X Direct ID System [ 506 ], and an 18plex named TYPER-X19 multiplex assay [ 507 ]. A collaborative study examined paternal and maternal mutations in X-STR markers [ 508 ]. A software program for performing population statistics on X-STR data was introduced [ 509 ] and sequence-based U.S. population data described for 7 X-STR loci [ 510 ].

3.4. New markers and approaches (microhaplotypes, InDels, proteomics, human microbiome)

In this section on new markers and approaches, publications related to microhaplotypes and insertion/deletion (InDel, or DIP for deletion insertion polymorphisms) markers are reviewed along with proteomic and microbiome approaches to supplement standard human DNA typing methods.

3.4.1. Microhaplotypes

Microhaplotype (MH) markers consist of multiple SNPs in close proximity (e.g., typically <200 bp or <300 bp) that can be simultaneously genotyped with each DNA sequence read using NGS. Two or more linked SNPs will define three or more haplotypes. Compared to STR markers, MHs do not have stutter artifacts (which complicate mixture interpretation), can be designed with shorter amplicon lengths in some cases (which benefits recovery of genetic information from degraded DNA samples), possess a higher degree of polymorphism compared to single SNP loci (which benefits discrimination power), and exhibit low mutation rates (which enables relationship testing and biogeographical ancestry inference). Thus, MH markers bring advantages to human identification, ancestry inference, kinship analysis, and mixture deconvolution to potentially assist missing person investigations, relationship testing, and forensic casework as discussed in several recent reviews [ 16 , 511 ]. A new database, MicroHapDB, has compiled information on over 400 published MH markers and frequency data from 26 global population groups [ 512 ].

A number of MH panels have been described [ [513] , [514] , [515] , [516] , [517] , [518] , [519] ]. Population data has been collected from a number of sources around the world including four U.S. population groups examined with a 74plex assay with 74 MH loci and 230 SNPs [ 520 ]. Various MH panels have been evaluated for effectiveness with kinship analysis [ [521] , [522] , [523] ]. Likewise the ability to detect minor contributors in DNA mixtures has been assessed [ [524] , [525] , [526] ].

3.4.2. InDel markers

InDel markers can be detected using a CE-based length analysis, and thus use instrumentation that forensic DNA laboratories already have. InDels can also be designed to amplify short DNA fragments (e.g., <125 bp) to help improve amplification success rates with low DNA quantity and/or quality. However, with only two possible alleles like SNPs, InDels are not as polymorphic as STRs and thus require more markers to obtain similar powers of discrimination as multi-allelic STR markers and do not work as well with mixed DNA samples. InDels possess a lower mutation rate than STRs and can be used as ancestry informative markers (AIMs) since allele frequencies may differ among geographically separated population groups.

Two commercial InDel kit exist: (1) Investigator DIPlex (QIAGEN, Hilden, Germany) with 30 InDels [ [527] , [528] , [529] , [530] , [531] ] and (2) InnoTyper 21 (InnoGenomics, New Orleans, Louisiana, USA) with 21 autosomal insertion-null (INNUL) markers [ [532] , [533] , [534] , [535] ]. In addition, a number of InDel assays have been published including a 32plex [ 536 ], a 35plex [ 537 ], a 38plex [ 538 ], a 39plex with AIMs [ 539 ], a 43plex [ 540 ], a 57plex [ 541 ], a 60plex with 57 autosomal InDels, 2 Y-chromosome InDels, and amelogenin [ 542 ], a 32plex with X-chromosome InDels [ 543 ], and a 21plex with AIMs [ 544 ].

A multi-InDel marker is a specific DNA fragment with more than one InDel marker located tightly in the physical position that provides a microhaplotype [ 545 ]. Several multi-InDel assays have been published include a 12plex [ 546 ] and an 18plex [ 547 ].

3.4.3. Proteomics

Protein analysis, often through immunological assays, has traditionally been used to identify body fluids and tissues. With improvements in protein mass spectrometry in recent years, genetic variation can be observed in hair shafts via single amino acid polymorphisms. Detection of these genetically variant peptides (GVPs) can infer the presence of corresponding SNP alleles in the genome of the individual who is the source of the protein sample. A thorough review of forensic proteomics in 2021 cited 375 references [ 18 ]. Recent efforts in this area have focused on using GVPs to differentiate individuals through their human skin cells [ [548] , [549] , [550] ] or hair samples [ [551] , [552] , [553] , [554] , [555] , [556] , [557] , [558] , [559] ]. An algorithm has been proposed for calculating random match probabilities with GVP information [ 560 ].

3.4.4. Human microbiome

Microorganisms live in and on the human body, and efforts are underway to utilize the human microbiome for a variety of potential forensic applications [ 21 , [561] , [562] , [563] ]. There are also active efforts with analysis of microbiomes in the environment (e.g., soil or water samples), which could be classified under non-human DNA testing. Forensic microbiome research covers at least six areas: (1) individual identification, (2) tissue/body fluid identification, (3) geolocation, (4) time since stain deposition estimation, (5) forensic medicine, and (6) post-mortem interval (PMI) estimation. Biological, technical, and data issues have been raised and potential solutions explored in a recent review article [ 21 ]. For example, microbes on deceased individuals are being studied to estimate the postmortem interval [ 20 ] and postmortem skin microbiomes were found to be stable during repeated sampling up to 60 h postmortem [ 564 ].

Sequence analysis of 16S rRNA using NGS provides information on the microbiome community present in a tested sample [ 565 ]. The Forensic Microbiome Database 46 correlates publicly available 16S rRNA sequence data as a community resource. If the skin microbiome is extremely diverse among individuals, then the potential exists to associate the bacterial communities on an individual's skin with objects touched by this individual assuming that the bacteria originating from the donor's skin are deposited (i.e., transfer to and persist on the surface) and can be detected and interpreted.

Specific aspects of the microbiome (e.g., the bacterial community) may be able to provide details about the donor through bacterial profiling. For example, in one study correlations were observed between the bacterial profile and gender, ethnicity, diet type, and hand sanitizer used [ 566 ]. Another study with 30 individuals found that each person left behind microbial signatures that could be used to track interaction with various surfaces within a building, but the authors concluded “we believe the human microbiome, while having some potential value as a trace evidence marker for forensic analysis, is currently under-developed and unable to provide the level of security, specificity and accuracy required for a forensic tool” [ 565 ].

Direct and indirect transfer of microbiomes between individuals has been studied [ 567 , 568 ] along with identifying background microbiomes [ 569 ] and the possibility of transfer of microbiomes within a forensic laboratory setting [ 570 ]. Changes in four bacterial species in saliva stains were charted, showing that it was possible to correctly predict deposition time within one week in 80% of the stains [ 571 ]. The ability to detect sexual contact has been explored through using the microbiome of the pubic region [ [572] , [573] , [574] ]. The microbiomes on skin, saliva, vaginal fluid, and stool samples have been compared [ 575 ]. The stability, diversity, and individualization of the human skin virome was explored with 59 viral biomarkers being found that differed across the 42 individuals studied [ 576 ]. It will be interesting to see what the future holds and what other findings come from this active area of research.

3.5. Kinship analysis, human identification, and disaster victim identification

Kinship analysis, which uses genetic markers and statistics to evaluate the potential for specific biological relationships, is important for parentage testing, disaster victim identification (DVI), and human identification of remains that may be recovered in missing person cases. New open-source software programs have been described that can assist with kinship analysis [ 577 , 578 ].

A potential biological relationship is commonly evaluated using a likelihood ratio (LR) by comparing the likelihoods of observing the genetic data given two alternative hypotheses, such as (1) an individual is related to another individual in a defined relationship versus (2) the two individuals not related. Higher LR values indicate stronger support with the genetic data if the proposed relationship is true. Multiple factors influence LR kinship calculations including the specific hypotheses, the genetic markers examined, the allele frequencies of the relevant population(s), the co-ancestry coefficient applied, and approaches to address potential mutations. STR genotypes were reported for 11 population groups used by the FBI Laboratory [ 579 ]. The status quo has been challenged in recent articles regarding how hypotheses are commonly established [ 580 ] and whether race-specific U.S. population databases should be used for allele frequency calculations [ 581 ].

Depending on the relationship being explored, information can be optimized through genetic information from additional known relatives or through collecting results at more loci [ 582 ]. Potential error rates have been modeled with the observation that false negatives, which occur when related individuals are misinterpreted as being unrelated, are more common than false positives, where unrelated people are interpreted as being related [ 583 ]. While LRs are generally reliable in detecting or confirming parent/child pairs, limitations of kinship determinations exist (e.g., distinguishing siblings from half-siblings) when using STR data [ 584 ].

Pairwise comparisons have been studied in forensic kinship analysis [ [585] , [586] , [587] ]. The effectiveness of 40 STRs plus 91 SNPs was shown to be better than 27 STRs and 91 SNPs or 40 STRs alone [ 588 ]. Only a minor increase in LRs was observed when taking NGS-generated allele sequence variation rather than fragment length allele variation [ 589 ]. The statistical power of exclusion and inclusion can be used to prioritize family members selected for testing in resolving missing person cases [ 590 ]. A strategy for making decisions when facing low statistical power in missing person and DVI cases was published [ 591 ].

The most challenging kinship cases involve efforts to separate pairs of individuals who are typically thought to be genetically indistinguishable (i.e., monozygotic twins) or distant relatives (e.g., fourth cousins) where there is an increased uncertainty in the possible relationship. In some situations, somatic mutations may permit distinguishing monozygotic twins following whole genome sequencing – and this approach was successful in four of six cases reported recently [ 19 ]. The probative value of NGS data for distinguishing monozygotic twins was explored [ 592 ]. A unique case of heteropaternal twinning was reported where opposite-sex twins apparently had different fathers [ 593 ]. An impressive effort in kinship analysis using direct-to-consumer genetic genealogy information from 56 living descendants of multiple genealogical lineages helped resolve a contested paternity case from over a century and a half ago to identify the biological father of Josephine Lyon [ 594 ].

Techniques for identification of human remains continue to improve particularly with the capabilities of NGS and hybridization capture [ 595 ] and ancient DNA extraction protocols [ 596 , 597 ]. Studies have reported variation in skeletal DNA preservation [ 598 ] and retrospectively considered success rates with compromised human remains [ 599 ].

A simulated airplane crash enabled six forensic laboratories in Switzerland to gain valuable DVI experience with kinship cases of varying complexity [ 600 ]. The ISFG Spanish-Portuguese Speaking Working Group likewise conducted a DVI collaborative exercise with a simulated airplane crash to explore fragment re-associations, victim identification through kinship analysis, coping with related victims, handling mutations or insufficient number of family references, working in a Bayesian framework, and the correct use of DVI software [ 601 ]. Other groups have explored the capability of a particular software tool [ 602 ] or implemented rapid DNA analysis to accelerate victim identification [ 603 ]. The International Commission on Missing Persons (ICMP) has gained considerable experience with DNA extraction and STR amplification from degraded skeletal remains and kinship matching procedures in large databases [ 604 ]. To supplement the INTERPOL DVI Guide, 47 some lessons learned and experienced-based recommendations for DVI operations have recently been provided [ 605 ].

3.6. Non-human DNA testing and wildlife forensics

Non-human biological evidence may inform criminal investigations when animals or plants are victims or perpetrators of crime or the presence of specific material, such as cat or dog hair, may contribute to reconstructing events at a crime scene. Non-human DNA testing includes wildlife forensics and domestic animal species as well as forensic botany and has many commonalities and some important differences compared to human DNA testing [ [606] , [607] , [608] , [609] , [610] ]. Pollen analysis can assist criminal investigations [ 611 , 612 ]. The potential for and the barriers associated with the wider application of forensic botany in civil proceedings and criminal cases have been examined [ 613 , 614 ].

Mammalian species identification can assist in determining the origins of non-human biological material found at crime scenes through narrowing the range of possibilities [ 615 ]. New sequencing methods have been developed to assist species identification [ 616 ]. A multiplex PCR assay was developed to simultaneously identify 22 mammalian species (alpaca, Asiatic black bear, Bactrian camel, brown rat, cat, cow, common raccoon, dog, European rabbit, goat, horse, house mouse, human, Japanese badger, Japanese wild boar, masked palm civet, pig, raccoon dog, red fox, sheep, Siberian weasel, and sika deer) and four poultry species (chicken, domestic turkey, Japanese quail, and mallard) [ 617 ]. A number of other species identification assays have also been reported [ [618] , [619] , [620] ].

An important effort for harmonizing canine DNA analysis is an ISFG working group known as the Canine DNA Profiling Group, or CaDNAP. 48 The CaDNAP group published an analysis of 13 STR markers in 1184 dogs from Germany, Austria, and Switzerland [ 621 ]. Six traits for predicting visible characteristics in dogs, namely coat color, coat pattern, coat structure, body size, ear shape, and tail length, were explored with 15 SNPs and six InDel markers [ 622 ]. Canine breed classification and skeletal phenotype prediction has been explored using various genetic markers [ 623 ]. A novel assay using a feline leukemia virus was developed to demonstrate that a contested bobcat was not a domestic cat hybrid [ 624 ] and a core panel of 101 SNP markers was selected for domestic cat parentage verification and identification [ 625 ].

DNA tests have been developed to assist with illegal trafficking investigations involving elephant ivory seizures [ 626 ], falcons [ 627 ], and precious coral material [ 628 ]. Accuracy in animal forensic genetic testing was explored with interlaboratory assessments performed in 2016 and 2018 [ 629 ]. A collaborative exercise conducted in 2020 and 2021 by the ISFG Italian Speaking Working Group examined performance across 21 laboratories with a 13-locus STR marker test for Cannabis sativa [ 630 ]. A molecular approach was explored to distinguish drug-type versus fiber-type hemp varieties [ 631 ].

Acknowledgments and disclaimer

I am grateful to Dominique Saint-Dizier from the French National Scientific Police for the invitation and opportunity to conduct this review and for the support of my supervisor, Shyam Sunder, for granting the time to work on this extensive review. Input and suggestions on this manuscript by Todd Bille, Thomas Callaghan, Kevin Kiesler, François-Xavier Laurent, Robert Ramotowski, Kathy Sharpless, and Robert Thompson are greatly appreciated. Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose.

1 https://www.sciencedirect.com/journal/forensic-science-international-genetics/special-issue/10TSDS4360H .

2 https://www.mdpi.com/journal/genes/special_issues/Forensic_Genetic .

3 https://www.mdpi.com/journal/genes/special_issues/forensic_mitochondrial_genomics .

4 https://www.mdpi.com/journal/genes/special_issues/Advances_Forensic_Genetics .

5 https://www.mdpi.com/books/pdfdownload/book/5798 .

6 https://www.mdpi.com/journal/genes/special_issues/Bioinformatics_Forensic_Genetics .

7 https://www.mdpi.com/journal/genes/special_issues/genetics_anthropology .

8 https://www.mdpi.com/journal/genes/special_issues/Identification_of_Human_Remains .

9 https://www.mdpi.com/journal/genes/special_issues/Forensic_DNA_analysis .

10 https://www.mdpi.com/journal/genes/special_issues/Forensic_DNA_Mixture .

11 https://www.mdpi.com/journal/genes/special_issues/28FBA0G4DH .

12 See https://www.swgdam.org/ .

13 https://www.swgdam.org/publications .

14 https://www.fbi.gov/file-repository/rapid-dna-guide-january-2022.pdf/view .

15 https://www.fbi.gov/file-repository/non-codis-rapid-dna-best-practices-092419.pdf/view .

16 https://www.fbi.gov/file-repository/rapid-dna-testing-for-non-codis-uses-considerations-for-court-073120.pdf/view .

17 https://www.justice.gov/olp/uniform-language-testimony-and-reports .

18 https://forensiccoe.org/human_factors_forensic_science_sourcebook/ .

19 https://www.nist.gov/organization-scientific-area-committees-forensic-science .

20 https://www.nist.gov/organization-scientific-area-committees-forensic-science/human-forensic-biology-subcommittee .

21 https://www.nist.gov/topics/organization-scientific-area-committees-forensic-science/wildlife-forensics-subcommittee .

22 https://www.aafs.org/academy-standards-board .

23 https://www.nist.gov/organization-scientific-area-committees-forensic-science/osac-registry .

24 See https://www.nist.gov/organization-scientific-area-committees-forensic-science/human-forensic-biology-subcommittee .

25 https://lexicon.forensicosac.org/ .

26 https://www.nist.gov/osac/human-factors-validation-and-performance-testing-forensic-science .

27 https://www.nist.gov/organization-scientific-area-committees-forensic-science/osac-research-and-development-needs .

28 https://www.gov.uk/government/publications/forensic-science-providers-codes-of-practice-and-conduct-2021-issue-7 .

29 https://www.aabb.org/standards-accreditation/standards/relationship-testing-laboratories .

30 https://www.isfg.org/DNA+Commission .

31 Previously available rapid DNA systems included the RapidHIT 200 from IntegenX and MiDAS (Miniaturized integrated DNA Analysis System) from the Center for Applied NanoBioscience at the University of Arizona.

32 See https://le.fbi.gov/science-and-lab-resources/biometrics-and-fingerprints/codis/rapid-dna .

33 See https://www.interpol.int/How-we-work/Forensics/DNA .

34 See https://www.interpol.int/How-we-work/Forensics/I-Familia .

35 See https://le.fbi.gov/science-and-lab-resources/biometrics-and-fingerprints/codis#Familial-Searching .

36 See https://isogg.org/wiki/Autosomal_DNA_testing_comparison_chart .

37 See https://www.wmar2news.com/infocus/maryland-quietly-shelves-parts-of-genealogy-privacy-law .

38 See https://www.hhs.gov/ohrp/regulations-and-policy/regulations/finalized-revisions-common-rule/index.html .

39 See https://enfsi.eu/about-enfsi/structure/working-groups/dna/ .

40 See https://www.swgdam.org/publications .

41 See https://www.chinesestandard.net/PDF/English.aspx/GAT815-2009 .

42 See https://strider.online/ .

43 See https://bit.ly/2R4bFgL (DNA-TrAC).

44 See https://cieqfmweb.uqtr.ca/fmi/webd/OD_CIEQ_CRIMINALISTIQUE (Transfer Traces Activity DataBase).

45 See https://www.visage-h2020.eu/index.html#publications .

46 See http://fmd.jcvi.org/ .

47 See https://www.interpol.int/en/How-we-work/Forensics/Disaster-Victim-Identification-DVI .

48 See https://www.isfg.org/Working+Groups/CaDNAP .

Appendix A Supplementary data to this article can be found online at https://doi.org/10.1016/j.fsisyn.2022.100311 .

Appendix A. Supplementary data

The following is the supplementary data to this article:

• DOI: 10.1177/01622439241266055
• Corpus ID: 271677014

Dissolving Boundaries, Fostering Dependencies. the new Forensic Genetics Assemblage

• Matthias Wienroth , Rafaela Granja
• Published in Science, Technology, &amp… 2 August 2024
• Law, Sociology
• Science, Technology, &amp; Human Values

77 References

Forensic dna phenotyping and its politics of legitimation and contestation: views of forensic geneticists in europe, governing anticipatory technology practices. forensic dna phenotyping and the forensic genetics community in europe, citizen science at the roots and as the future of forensic genetic genealogy, bridging disciplines to form a new one: the emergence of forensic genetic genealogy, socio-technical disagreements as ethical fora: parabon nanolab’s forensic dna snapshot™ service at the intersection of discourses around robust science, technology validation, and commerce, governing expectations of forensic innovations in society: the case of fdp in germany, the low template dna profiling controversy: biolegality and boundary work among forensic scientists, opening up forensic dna phenotyping: the logics of accuracy, commonality and valuing, technological innovations in forensic genetics: social, legal and ethical aspects., public participation in genetic databases: crossing the boundaries between biobanks and forensic dna databases through the principle of solidarity, related papers.

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ORIGINAL RESEARCH article

The forensic aspects of suicide and neurotrophin factors: a research study.

• 1 Department of Clinical and Experimental Medicine, Section of Legal Medicine, University of Foggia, Foggia, Italy
• 2 Department of Medical Sciences, Section of Legal Medicine University of Ferrara, Ferrara, Italy
• 3 Department of Biomedical, Metabolic and Neural Sciences, Institute of Legal Medicine, University of Modena and Reggio Emilia, Modena, Italy

Introduction: Suicide represents a significant public health problem whose neurobiology is not yet fully understood. In many cases, suicidal behavior and psychiatric spectrum disorders are linked, in particular, to major depression. An emerging pathophysiological hypothesis underlines the role of neurotrophic factors, proteins involved in neurogenesis, in synaptic plasticity in response to stressors. Our research aims to evaluate the degree of expression of brain neurotrophic factor (BDNF) in brain areas involved in depressive disorder in suicidal subjects. Furthermore, we want to evaluate the expression of glial cell line-derived neurotrophic factor (GDNF) in suicidal subjects.

Methods: We selected twenty confirmed cases of suicide among subjects with a clinical history of depressive pathology and possible psychopharmacological treatment, compared to ten controls of individuals who died of non-suicidal causes. For all selected cases and controls, immunohistochemical investigations were performed using a panel of antibodies against the BDNF and GDNF antigens on samples from the various brain areas.

Results and discussion: The results show that BDNF was under-expressed in the cerebral parenchyma of subjects who died by suicide compared to controls, while there was an overexpression of GDNF in suicide victims, these data could be useful for a clinical application as potential markers for suicidal risk, to assess the severity of depression and development of specific pharmacological therapies for depression.

1 Introduction

According to the WHO, every year, about 700,000 people end their lives through suicide, making it the fourth leading cause of death in young people ( datadot, 2024 ). According to estimates, for every suicide carried out, there are between 10 and 40 suicide attempts ( Krug et al., 2002 ; Chang et al., 2011 ). Suicide turns out to be a real social problem, as it cannot leave public opinion indifferent. According to ISTAT (Italian National Institute of Statistics) data from 2016, 3780 committed suicides in Italy, 78.8% of whom were male. The death rate from suicide is 11.8 per 100,000 population for men and 3.0 per 100,000 population for women ( Vichi et al., 2019 ). In Western countries, the suicide rate among men is three to four times higher than among women. This difference is likely to be the case because men use reliably more lethal means of taking their own lives. This difference is even more marked in men aged 65 years and older, who are likely to be ten times more than women ( Sue et al., 2016 ). In the Eastern Mediterranean countries, on the other hand, female and male suicide rates are almost identical. In many countries, suicide rates appear to be higher in middle age or old age. The absolute number of suicides, however, is highest in the age group between 15 and 29 years old ( Pitman et al., 2012 ; Yip et al., 2012 ). Suicide is also related to age, with young people under 25 and older adults interested the most in the risk of suicide, although it proportionally increases with age ( OECD, 2012 ). In 2018, the ISTAT estimated that 3,820 people committed suicide, with the highest incidence in males between 35 and 64 years old. The main methods used to commit suicide are hanging, pesticide poisoning, and the use of firearms. In a survey ( Ajdacic-Gross et al., 2008 ) carried out in 56 countries, hanging was by far the most common method used by 53% of male suicides and 39% of female suicides ( O Connor et al., 2011 ; Suicide in the Province, 2022 ). Suicide presents numerous risk factors ( Beghi et al., 2021 ; Risk and Protective Factors, 2023 ), such as individuals (previous suicide attempts, chronic psychiatric and physical pathologies, drug addiction), relationships (history of family suicide, isolation, bullying), community (violence, discrimination), and social-linked (spectacularization by the media, access to lethal means). One of the most important risk factors is the presence of psychiatric pathology, primarily major depression, followed by anxiety disorder, bipolar disorder, and drug addiction ( Beghi et al., 2021 ). Also, genetics can influence the risk of committing a self-suppressive act ( Brent and Melhem, 2008 ). Among psychiatric pathologies, it is clear that patients suffering from major depression present a significant risk of suicide or attempted suicide ( Conejero et al., 2018 ; Fusar-Poli et al., 2021 ). Identifying risk factors can recognize a part of the population at high risk of committing extreme acts ( Granier and Boulenger, 2002 ).

The neurobiology underlying suicide is exceptionally complex, not being the result of a single pathophysiological entity but of a multiplicity of behavioral, socio-environmental, and psychological causal factors that act together simultaneously. According to the literature, suicide follows the “diathesis-stress” model: a behavioral disorder derives from a genetic predisposition that makes one more vulnerable to stress, usually caused by life events ( Mann, 2003 ; Van Heeringen and Mann, 2014 ; Zeigler-Hill and Shackelford, 2019 ). In particular, traumatic life events and stress acts as triggers for suicidal behavior ( Dwivedi, 2012 ). Furthermore, the interaction of numerous biological systems is involved ( Girardi and Pompili, 2015 ), including the neurotrophic system. Indeed, the pathogenesis of depression and suicidal behavior involves changes in neuronal plasticity ( Garcia, 2002 ), reducing the brain’s ability to adapt.

Neurotrophins are growth factors that play a crucial role in regulating structural and synaptic plasticity, maintaining neuronal functions, and modulating neurotransmission ( Thoenen, 1995 ). Neurotrophins are essential for the survival, growth, and regeneration of different neuronal populations belonging to the central and peripheral nervous systems in the fetal and adult brain ( Allen et al., 2013 ). The first neurotrophin discovered in the 1950s was Nerve Growth Factor (NGF) ( Levi-Montalcini, 1987 ). Neurotrophin is transported from the production site to the nerve terminal via axonal retrograde flow during development. Neurons that present this retrograde flow survive; otherwise, they degenerate (“neurotrophic hypothesis”) ( Hamburger et al., 1981 ; Ginty and Segal, 2002 ). There are five neurotrophic factors expressed in mammals: Brain-Derived Neurotrophic Factor (BDNF), Neurotrophins 3 and 4 (NT-3 and NT-4), Glial Derived Neurotrophic Factor (GDNF) and Ciliar Neurotrophic Factor (CNTF). Neurotrophins are initially synthesized as pro-neurotrophins, and then through proteolytic processes, they are converted into mature neurotrophins that interact with two classes of receptors (p75NRT and Trk) to act ( Ibáñez and Simi, 2012 ; Neurotrophic, 2017 ). Neurotrophins also have numerous actions outside the nervous system, such as immune ( Thorpe and Perez Polo, 1987 ; Otten et al., 1989 ; Donovan et al., 2000 ) and hematopoietic function ( Thorpe et al., 1987 ). They also control some neuroendocrine functions (for example, the development of the female rat’s hypothalamus) ( Ojeda et al., 1991 ) and are involved in the transmission of pain ( Skaper, 2017 ). Furthermore, these molecules can increase cholinergic function and protect against neurodegeneration ( Hock et al., 2000 ; Hoxha et al., 2018 ), hypothesizing a role in Alzheimer’s disease ( Hefti, 1986 ). Similarly, the GDNF can be involved in Parkinson’s disease, as it acts on dopaminergic neurons ( Yasuda and Mochizuki, 2010 ). Therefore, a pathological alteration of neurotrophic factors could determine defects in neural maintenance and regeneration, possible structural anomalies in the brain, and a reduction in neural plasticity, thus compromising the individual’s ability to adapt in critical situations.

BDNF (“Brain-Derived Neurotrophic Factor”) is the most widespread neurotrophin in the brain of mammals, both in adults and in the developing phase ( Anisman et al., 2012 ). It is involved in neurogenesis, the development of neurons, neuronal homeostasis, the structural integrity and maintenance of neuronal plasticity in the adult brain ( Altar et al., 1997 ; Bartrup et al., 1997 ; Edelmann et al., 2014 ; Panja and Bramham, 2014 ), synaptic connection, in the mechanisms that regulate learning and memory ( Kang and Schuman, 1995 ), drug addiction, and in stress adaptation mechanisms. Numerous exogenous and endogenous stimuli (such as stress, physical activity, diet, and brain injury) regulate BDNF expression ( Aid et al., 2007 ; Pruunsild et al., 2007 ). Several neuropathologies cause a reduction in BDNF protein levels and serum in patients’ brains ( Autry and Monteggia, 2012 ; Borba et al., 2016 ). Unfortunately, it is unclear whether serum BDNF levels reflect brain levels, as studies contradict each other ( Sartorius et al., 2009 ; Klein et al., 2011 ). However, serum BDNF levels should be higher than those in plasma and cerebrospinal fluid ( Radka et al., 1996 ; Serra-Millàs, 2016 ). According to some clinical studies that examined the blood levels of BDNF in vivo , the BDNF can cross the blood-brain barrier in both directions via a high-capacity saturable transport system, which determines an early influx and rapid in the brain ( Pan et al., 1998 ). BDNF concentrations can be measured in serum, plasma, or whole blood and appear highly correlated to those in cerebrospinal fluid. Therefore, BDNF levels in the blood could be related to the concentration of the same neurotrophin at the level of the cerebral cortex ( Klein et al., 2011 ). The blood quantification of BDNF in vivo could be a marker of neuronal plasticity ( Shimizu et al., 2003 ). Furthermore, BDNF also plays an essential role in neuroinflammation and aging, identifying a role in degenerative diseases such as Parkinson’s and Alzheimer’s ( Lima et al., 2019 ). In humans, BDNF is considered a promising biomarker for various psychiatric pathologies ( Chen et al., 2017 ). In some animal models, mice heterozygous for the BDNF gene showed increased aggression and anxiety, significant weight gain, and memory impairment, suggesting that its depletion could be associated with the development of some psychiatric symptoms ( Lindholm and Castracn, 2014 ). This hypothesis also seems supported by the fact that there is an increase in BDNF levels after treatment of psychiatric pathologies ( Nuernberg et al., 2016 ; Castrén and Monteggia, 2021 ). Patients with major depression show an appreciable reduction in serum levels of BDNF ( Shimizu et al., 2003 ), probably due to a reduction of the protein in the brain ( Karege et al., 2005a ). There is also a single nucleotide polymorphism of the BDNF gene (Val66Met) that is associated with the severity of depressive symptoms and memory deficits ( Youssef et al., 2018 ; Zhao et al., 2018 ), as well as a higher risk of suicide attempts ( Zai et al., 2012 ). Typically, treatment with antidepressant drugs increases BDNF levels in serum and plasma ( Molendijk et al., 2011 ). Some post-mortem studies have shown that treatment-resistant patients had significantly low levels of BDNF, especially in areas such as the hippocampus, which otherwise is generally rich ( Colla et al., 2007 ; Brunoni et al., 2014 ). Other studies have demonstrated reductions in levels of BDNF mRNA and its protein from post-mortem brain samples of depressed patients, in particular in the hippocampus and amygdala ( Guilloux et al., 2012 ; Ray et al., 2014 ). The reduction of serum BDNF levels has also been ascertained in other psychiatric pathologies, such as schizophrenia ( Ray et al., 2014 ), autism ( Katoh Semba et al., 2007 ), and bipolar disorder ( Fernandes et al., 2015 ). Furthermore, in animal models, BDNF levels in the prefrontal cortex and hippocampus were increased after pharmacological treatment with mood stabilizers ( Yasuda et al., 2009 ; Jornada et al., 2010 ). In the literature, there are numerous studies carried out on the brains of suicidal victims, which observe a reduction in the levels of BDNF protein and its receptor in the hippocampus ( Karege et al., 2005a ; University, 2021 ) and the prefrontal cortex ( Zheng et al., 2016 ; Misztak et al., 2020 ), as well as in its mRNA ( Hamburger et al., 1981 ). Thus, BDNF levels could represent an interesting biological marker of suicidal behavior.

Glial cell line-derived neurotrophic factor (GDNF) is a neurotrophin expressed primarily during neuronal development and differentiation. In the adult, its expression decreases and remains limited to some regions, such as the cortex, the hippocampus, the substantia nigra, and the striatum nucleus ( Duarte Azevedo et al., 2020 ). GDNF promotes the differentiation of dopaminergic ( Christophersen et al., 2007 ) and serotonergic ( Ducray et al., 2006 ) neurons. Furthermore, one of its most important roles is the protection of neurons ( Hochstrasser et al., 2011 ; Uzdensky et al., 2013 ; Jaumotte and Zigmond, 2014 ) from oxidative stress and inflammation ( Pascual et al., 2008 ). GDNF levels appear to be reduced in patients who have Alzheimer’s disease, leading to the hypothesis of its use as a biomarker for the pathology [ ( Sharif et al., 2021 ; Kimhy et al., 2015 )]. Although there are not many studies in the literature relating to the involvement of GDNF in the suicidal phenomenon, there is evidence linking this neurotrophin to the onset of mood disorders. In fact, according to some studies, there are lower serum GDNF levels in patients suffering from depression, with a subsequent increase after pharmacological treatment ( Lin and Tseng, 2015 ; Wang et al., 2023 ). In a post-mortem study, an increase in GDNF was observed in the parietal cortex (site of emotion regulation ( Anderson et al., 2004 )) of patients with depressive disorder ( Michel et al., 2008 ), while in other studies, a reduction in the expression of its mRNA was measured ( Otsuki et al., 2008 ). In the literature, GDNF levels increase following ischemic or inflammatory damage ( Wei et al., 2000 ; Michel et al., 2007 ) as neuronal resilience and plasticity compromise, hypothesizing that the increase in GDNF is an adaptive and compensatory response to neuronal damage ( Chao and Lee, 1999 ; Tokumine et al., 2003 ).

Currently, many studies on the possible link between neurotrophins and suicide are carried out in vivo or plasma ( Kim et al., 2007 ; Salas Magana et al., 2017 ; Sonal and Raghavan, 2018 ). Further interesting data could come from post-mortem studies carried out directly on the brains of suicidal subjects. An essential element is that many of these studies focus on the link between neurotrophins and neuro-psychiatric pathology. However, not all subjects who commit suicide suffer from a diagnosed psychiatric pathology. A recent literature review ( De Simone et al., 2022 ) shows a paucity of experimental work on BDNF and GDNF. It shows that the altered regulation of BDNF, such as the Val66Met polymorphism, can favor the onset of psychiatric disorders linked to stress ( Felmingham et al., 2013 ; Zhao et al., 2018 ; Miao et al., 2020 ), leading to an increase in suicidal risk according to some works ( Zai et al., 2012 ; Paska et al., 2013 ), or no correlation with suicide, according to another study ( Ratta-apha et al., 2013 ). Some of the studies examining the level of BDNF in post-mortem brain samples showed reduced values compared to controls, regardless of psychiatric diagnosis, in the prefrontal cortex and hippocampus ( Dwivedi et al., 2003 ; Karege et al., 2005b ; Ducray et al., 2006 ; Hochstrasser et al., 2011 ), as well as in the amygdala ( Ray et al., 2014 ) and the anterior cingulate cortex ( Tripp et al., 2012 ) of subjects suffering from major depressive disorder. Schneider et al. (2015) also evaluated subjects suffering from depression, detecting increased methylation of the BDNF promoter in the frontal cortex, in agreement with other studies ( Keller et al., 2010 ; Kang et al., 2013 ). Another interesting finding, supported by further evidence ( Pan et al., 1998 ; Klein et al., 2011 ), is that the brain level of BDNF was higher in suicidal subjects suffering from major depression on pharmacological therapy compared to non-suicidal controls ( Gadad et al., 2021 ). As regards GDNF, in the study by Michel et al. ( Michel et al., 2007 ), it was not possible to demonstrate a statistically significant increase in the levels of this neurotrophin in different brain areas of depressed patients taking antidepressant drug therapy.

The results of this systematic review partially support the hypothesis that a lower level of neurotrophins is connected to an increased risk of suicide. The identification of a suicide biomarker remains a challenge for the scientific and forensic community. The objective of the present study is to analyze the correlation between suicide and the degree of expression of BDNF and GDNF on autopsy samples in specific brain areas. These neurotrophic factors could have an important role both in the prevention of suicidal events in the population at high risk for anti-conservative behavior, allowing early action to limit this risk preventively, and in the search for a new potential pharmacological target. In the literature, there are no valuable markers for the identification of suicidal risk, so BDNF and GDNF could be promising for identifying suicidal risk in people with well-defined risk factors.

2 Materials and methods

2.1 sample selection.

We conducted a retrospective study based on a series of judicial autopsies performed at the Forensic Medicine of the University of Foggia and the University of Ferrara.

The sample consists of twenty subjects who died following suicide between November 2020 and March 2023 ( Table 1 ). The autopsies were performed 36–48 after the death and we excluded from the study corpses in an advanced stage of decomposition, corpses testing positive for common substances of abuse, and subjects suffering from neurodegenerative diseases, Alzheimer’s, and Parkinson’s disease. For subjects who used drugs, only benzodiazepines in three cases, we dosed the active ingredients, ensuring that they were at therapeutic doses (between 2 and 5 mg/day). We selected ten case controls, chosen among subjects who died of natural or only chest traumatic causes, without a history of psychiatric pathology or drug addiction, and who were negative for toxicological analyses.

Table 1 . The table shows the main information on the selected cases.

In our sample, six individuals did not have a psychiatric diagnosis. However, they presented particularly critical and stressful recent events (e.g., bereavement, loss of job, imprisonment). The remaining fourteen cases, however, had a known psychiatric pathology; of these, six were affected by mood disorders (five from major depressive disorder, one from bipolar disorder), eight from other types of diagnosed psychiatric pathology (pathological gambling, substance use disorder, problematic use of alcohol, autism spectrum disorder, self-harm, adjustment disorder). The characteristics of these disorders are summarized in Table 2 based on the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5). In all cases, we performed toxicological analyses on biological fluids to test the primary substances of abuse and the most common pharmacological active ingredients.

Table 2 . The table shows the most relevant features of psychiatric disorders diagnosed in the selected cases, based on the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5).

To exclude a possible influence of psychopharmacological active ingredients on the expression of BDNF and GDNF, we excluded subjects treated with antidepressant and antipsychotic drugs or positive for narcotic substances. Three of the twenty subjects studied regularly took only a mild therapy with sedative drugs (benzodiazepines), whose active ingredients, based on the results of toxicological analyses, still fell within the therapeutic prescribed dosage range.

2.2 Methods

For each case, the entire brain was removed during the autopsy examination, with appropriate preservation in formol solution for 3 weeks to perform a correct fixation of the tissues. The brain was dissected using sagittal cuts, identifying and taking four areas of interest from the right hemisphere: the prefrontal cortex, cingulate gyrus, basal nuclei, and hippocampus.

All the samples obtained were embedded in paraffin and treated by immunohistochemical staining for anti-BDNF and anti-GDNF antibodies to proceed with the search for neurotrophins. The two antibodies used are BDNF (monoclonal mouse antibody Catalog Number: 66292-1-ig, Proteintech Group, Chicago, United States), and GDNF (monoclonal rabbit antibody, Catalog Number: orb572592, Biorbyt Ltd., Cambridge, United Kingdom). For both antibodies, it was used the Protein Atlas website for the selection of positive and negative controls, and then it was performed various tests for the individuation of the correct pretreatment and dilution, according to the indications of the Production Company, published papers, and the suggestions of www.atlasantibodies.com .

For each case, sections of approximately 4 μm were made on the microtome. The sections, mounted on a slide, were hydrated in decreasing alcohol solutions. After inhibiting endogenous peroxidase, the sections were subjected to antigen retrieval in Citric acid 0.1 M and subsequently incubated with the primary antibody (dilution 1:200 for BDNF and 1:500 for GDNF). The formation of the immune complex was highlighted by applying a Streptavidin-Biotin system (HRP-DAB system research and development kit CTS005, R&D Systems, Inc., Minneapolis, MN, United States). The reaction was visualized by peroxidation of 3,3′-diaminobenzidine (DAB). Once the reaction was verified, the nuclei were counter-stained with hematoxylin, and subsequently slides were subjected to dehydration. The slide was then mounted and observed using a Nikon Eclipse E90i optical microscope, using the NIS – Elements F program. BDNF and GDNF immunopositivity in the right frontal cortex, hippocampus (dentate gyrus (DG) -Lacunar-molecular, Radiate, Granular layers and Hilus:.), girus of the cingulum, and basal nuclei. For the hippocampus, the granular layer and hilus are the selected areas for the statistical analysis because they are more significant. Four visual fields of approximately 350 μm × 350 μm were randomly selected in interest of each area for each sample of cases and controls. Images for each slide were acquired with a digital camera (Nikon) connected to the microscope at 10x for an exhaustive semiquantitative, preliminary evaluation of the reaction and after at 40 × magnification in the more significant area for quantification. The parameters for image acquisition were established at the beginning of the observation and kept constant for all images. Quantifying cells positive for DAB staining was performed using ImageJ software (imagej.nih.gov/ij/) and expressed as the number of positively stained cells per analyzed area. Quantifications were expressed as the number of positive-stained cells/analyzed area. For hippocampus we quantized the radiate layer and hilus because are the areas. Blind researchers performed histological analyses concerning the information about the cases. The blinding of the data was maintained until the analysis was terminated.

2.3 Statistic analysis

Data were analyzed using Windows GraphPad Prism 10 software for Windows (La Jolla, CA, United States). The data were analyzed through the two-way ANOVA analytical system (two-way ANOVA) for two independent factors. A P -value < 0.05 was considered statistically significant. Results are expressed as means ± standard deviation.

3.1 Prefrontal cortex

The two-way ANOVA highlighted a statistically significant difference in both cases ( p < 0.0001). In particular, a reduced expression of BDNF was noted in suicide cases compared to controls, while the expression of GDNF was increased in cases compared to controls ( Figures 1 , 2 ).

Figure 1 . BDNF immunohistochemical expression in the prefrontal cortex. Prefrontal cortex immunohistochemistry results: normal immunohistochemistry reaction of BDNF in the control case, see arrows (A) 10x magnification (B) 40x magnification; reduced expression of BDNF in a sample of suicide cases, see arrows (C) 10x magnification (D) 40x magnification. In the lower part of the figures, the graphical representation of the statistical analysis, the percentage decrease of BDNF in the suicide cases group is 24%.

Figure 2 . GDNF immunohistochemical expression in the prefrontal cortex. Prefrontal cortex immunohistochemistry results: basal immunohistochemistry reaction of GDNF in thecontrol case (the control case used is the same as Figure 1 , you can see in consecutive slice section the difference of reaction between the two markers), see arrows (A) 10x magnification (B) 40x magnification; over-expression of GDNF in a sample of suicide case, see arrows (C) 10x magnification (D) 40x magnification. The graphical representation of the statistical analysis is in the lower part of the figures.

3.2 Hippocampus

The application of the two-way ANOVA test returned a statistically significant difference between the expression of BDNF ( p < 0.001) and GDNF (<0.0001). In particular, it was possible to highlight a reduced expression of BDNF in suicide cases compared to controls, while the expression of GDNF was found to be increased in cases compared to controls ( Figures 3 , 4 ).

Figure 3 . BDNF immunohistochemical expression in the hippocampus. Hippocampus (dentate gyrus) immunohistochemistry results: normal immunohistochemistry reaction of BDNF in the control case (granular layer of dentate gyrus), see arrows (A) 10x magnification (B) 40x magnification; reduced expression of BDNF in a sample of suicide case (granular layer of dentate gyrus), see arrows (C) 10x magnification (D) 40x magnification. In the lower part of the figures, the graphical representation of the statistical analysis, the percentage decrease of BDNF in the suicide cases group is 27%.

Figure 4 . GDNF immunohistochemical expression in the hippocampus. Hippocampus (dentate gyrus) immunohistochemistry results: basal immunohistochemistry reaction of GDNF in the control case (hilus of dentate gyrus), see arrows (A) 10x magnification (B) 40x magnification; over-expression of GDNF in a sample of suicide case (granular layer of dentate gyrus), see arrows (C) 10x magnification (D) 40x magnification. In the lower part of the figures is the graphical representation of the statistical analysis.

3.3 Gyrus of the cingulum

The two-way ANOVA analysis highlighted a statistically significant difference in both cases ( p < 0.0001). In particular, a reduced expression of BDNF was noted in suicide cases compared to controls, although less marked than in the other areas examined. Also, in this case, the expression of GDNF is increased in cases compared to controls ( Figures 5 , 6 ).

Figure 5 . BDNF immunohistochemical expression in cingulum. Cingulum immunohistochemistry results: normal immunohistochemistry reaction of BDNF in the control case, see arrows (A) 10x magnification (B) 40x magnification; reduced expression of BDNF in a sample of suicide cases, see arrows (C) 10x magnification (D) 40x magnification. In the lower part of the figures, the graphical representation of the statistical analysis shows that the percentage decrease of BDNF in the suicide cases group is 21%.

Figure 6 . GDNF immunohistochemical expression in cingulum. Cingulum immunohistochemistry results: basal immunohistochemistry reaction of GDNF in the control case, see arrows (A) 10x magnification (B) 40x magnification; over-expression of GDNF in a sample of suicide case, see arrows (C) 10x magnification (D) 40x magnification. The graphical representation of the statistical analysis is in the lower part of the figures.

3.4 Basal nuclei

The two-way ANOVA showed a statistically significant difference in the expression of BDNF ( p < 0.001), while no statistically significant differences were highlighted in GDNF ( p < 0.1). In particular, a reduced expression of BDNF was noted in suicide cases compared to controls, while a minimal increase in GDNF expression was observed in cases compared to controls ( Figures 7 , 8 ).

Figure 7 . BDNF immunohistochemical expression in basal nuclei. Basal nuclei immunohistochemistry results: normal immunohistochemistry reaction of BDNF in the control case, see arrows (A) 10x magnification (B) 40x magnification; reduced expression of BDNF in a sample of suicide case, see arrows (C) 10x magnification (D) 40x magnification. In the lower part of the figures, the graphical representation of the statistical analysis shows that the percentage decrease of BDNF in the suicide cases group is 21%.

Figure 8 . GDNF immunohistochemical expression in basal nuclei. Basal nuclei immunohistochemistry results: basal immunohistochemistry reaction of GDNF in the control case, see arrows (A) 10x magnification (B) 40x magnification; similar basal expression of GDNF in a sample of suicide case, see arrows (C) 10x magnification (D) 40x magnification. In the lower part of the figures is the graphical representation of the statistical analysis.

4 Discussion

There are few studies in the literature relating to the measure of BDNF and GDNF on post-mortem samples of suicidal subjects, especially those without psychiatric pathologies. Our work aims to contribute to science to identify molecules useful as markers of suicide risk. These neurotrophins could also be potential pharmacological targets for researching and developing new targeted therapies.

The sample examined in our study was composed of twenty subjects who died by suicide and ten controls who died of non-suicidal causes, matched for sex and age, who underwent autopsy examination. 90% of subjects were male (18 of 20), 10% were female (2 of 20), 13 of them (65%) were under 50 years old, and 7 (35%) were over 50 years old. Furthermore, 6 out of 20 individuals (30%) did not have any diagnosis of psychiatric disorder. However, they had been involved in recent stressful events, for example, bereavement, job loss, and imprisonment. The remaining 14 cases (70%), however, presented a psychiatric pathology; of these, six were affected by mood disorders (five from major depressive disorder, one from bipolar disorder), eight from other types of diagnosed psychiatric pathology (pathological gambling, substance use disorder, problematic use of alcohol, autism spectrum disorder, self-harm, adjustment disorder). Five of the 20 cases analyzed (25%) were subjects subjected to a prison regime, another risk factor.

To exclude the possible influence of psychopharmacological active ingredients on the expression of BDNF and GDNF, the authors excluded patients on therapy with antidepressant and antipsychotic drugs and those who tested positive for narcotic and psychoactive substances in the toxicological analyses. Therefore, subjects who committed suicide due to overdose were also excluded. Only three of the 20 subjects studied were taking mild therapy based on non-neuroleptic or antidepressant drugs (mainly benzodiazepines) whose active ingredients, based on the results of toxicological analyses, were still within the therapeutic dosage range.

11 out of 20 subjects (55%) died from hanging [the most used method, according to literature data ( Baldari et al., 2021 )], 4 out of 20 (20%) from precipitation, 2 out of 20 (10%) from stab wounds, 2 in 20 (10%) by drowning and 1 in 20 (5%) by gunshot wounds.

The results of our work, which used an immunohistochemical method widely used in the field of forensic pathology ( Baldari et al., 2021 ), highlighted a statistically significant reduction in BDNF levels in the various brain regions examined in all twenty suicidal subjects compared to the ten controls. In particular, the areas most affected are the prefrontal cortex and cingulate gyrus ( p < 0.0001), to a slightly lesser extent, hippocampus and basal nuclei ( p < 0.001). These data agree with the literature ( Middlemas et al., 1991 ; Karege et al., 2002 ; Dwivedi et al., 2003 ; Karege et al., 2005b ; Tripp et al., 2012 ), which reports significant decreases in BDNF levels in the prefrontal cortex, hippocampus, and cingulate gyrus. Furthermore, it is interesting to consider that the global examination of the different brain areas highlighted a statistically significant reduction in BDNF in suicidal subjects compared to controls ( p < 0.0001).

The encephalic expression of GDNF was increased in all 20 study subjects. In particular, the authors observed a statistically significant ( p < 0.0001) increase in GDNF in suicidal subjects compared to controls at the prefrontal cortex, hippocampus, and cingulate gyrus. In the basal nuclei of suicidal subjects, however, there was a slight increase in GDNF levels compared to controls, which was not statistically significant. Interestingly, the global examination of the different brain areas highlighted an increase in GDNF in suicidal subjects, compared to controls, which was statistically significant ( p < 0.0001).

Our research is unique, as we analyzed the expression of GDNF on the brain tissue of suicidal subjects without therapy. The few studies in the literature on GDNF have evaluated its concentration in the peripheral blood of patients with depressive or, more generally, mood disorders.

The results obtained agree with the data of another work ( Rosa et al., 2006 ), which documented an increase in GDNF in the peripheral blood of patients who have bipolar disorder in the depressive phase. Thus, increased BDNF synthesis could be a characteristic of acute episodes of mood disorders, although the literature is unclear ( Takebayashi et al., 2006 ; Otsuki et al., 2008 ).

An important point of the study is that we have only selected autoptic cases of subjects who have not undergone drug therapy. In literature, most of the studies concern subjects on antidepressant drug therapy, finding a reduction in the expression of GDNF in plasma or blood ( Maheu et al., 2015 ). On the contrary, in our study, the GDNF molecule in the brain is increased. It suggests that central GDNF signaling may represent a novel target for antidepressant treatment ( Maheu et al., 2015 ).

In our study, we evaluate neurotrophic expression at the brain tissue, while other studies evaluate it at the plasma peripheral level ( Sun et al., 2019 ). It would be interesting to conduct a multidisciplinary clinic-based assessment to observe whether the reduction in GDNF correlates with an improvement in symptoms.

The authors analyzed three further subgroups of the 20 cases: six subjects suffering from psychiatric pathology, eight subjects suffering from mood disorders, and six normal subjects. This analysis revealed a statistically significant reduction ( p < 0.0001) in the expression of BDNF in all psychiatric subjects compared to the control group in all encephalic areas. In contrast, no statistically significant variations appeared in comparison between depressed individuals and those with other mental disorders. The same result was obtained with the GNDF, with a statistically significant increase ( p < 0.0001) in all brain areas of psychiatric subjects compared to the control group. In contrast, there were no statistically significant variations in the comparison between depressed individuals and those with other psychic disorders.

5 Conclusions

The results we obtained on the expression of BDNF and GDNF, in agreement with data from works published in the literature, support the hypothesis that lower levels of BDNF and higher levels of GDNF correlate with an increased risk of suicide. The use of these markers could have several clinical implications. BDNF and GDNF testing could be valuable markers for screening patients most at risk of suicide based on demographic and clinical data to estimate suicidal risk. These markers measured in vivo and correlated with clinical symptomatology could help assess the severity of depressive symptoms, such as the presence of polymorphism of the BDNF gene (Val66Met). Further studies could have important clinical implications using BDNF and GDNF as targets for specific pharmacological therapies for depression.

This study could be a pilot study to continue the research on a larger sample of subjects who died as a result of suicide. It would, therefore, be necessary to increase the sample size, standardize the data collection methods, and group the samples according to their characteristics. In our study, there is a wide heterogeneity regarding the method of suicide and psychiatric pathology. In addition, the exclusion of psychoactive substance users may have led to a selection bias, although it was necessary to identify the modification in BDNF and GDNF correctly.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement

The studies involving humans were approved by Ethics Committee N 57/CE/ 2024 of the “Riuniti” Hospital of Foggia, Italy. The studies were conducted in accordance with the local legislation and institutional requirements. The study was performed in accordance with the guidelines of the Declaration of Helsinki. This study was performed by using human post-mortem brain samples collected during autopsies ordered by the prosecutor and used at the end of the investigations; It is a retrospective study on samples collected during the autopsy, and the acquisition of informed consent is not possible, because the heirs cannot be traced.

Author contributions

SD: Writing–review and editing, Writing–original draft, Resources, Validation, Conceptualization, Project administration. LA: Software, Writing–review and editing, Visualization, Writing–original draft, Resources. MAB: Writing–original draft, Formal Analysis. SC: Writing–original draft, Investigation, Supervision. MC: Writing–review and editing, Writing–original draft. LC: Methodology, Project administration, Writing–review and editing. MN: Conceptualization, Writing–original draft, Investigation, Project administration, Validation, Writing–review and editing, Supervision.

The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Acknowledgments

Thanks to Dott.ssa Mika and Dott.ssa Formalina for the friendly and constant support.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.

Publisher’s note

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Aid, T., Kazantseva, A., Piirsoo, M., Palm, K., and Timmusk, T. (2007). Mouse and rat BDNF gene structure and expression revisited. J Neurosci. Res. 85, 525–535. doi:10.1002/jnr.21139

PubMed Abstract | CrossRef Full Text | Google Scholar

Ajdacic-Gross, V., Weiss, M. G., Ring, M., Hepp, U., Bopp, M., Gutzwiller, F., et al. (2008). Methods of suicide: international suicide patterns derived from the WHO mortality database. Bull. World Health Organ 86, 726–732. doi:10.2471/blt.07.043489

Allen, S. J., Watson, J. J., Shoemark, D. K., Barua, N. U., and Patel, N. K. (2013). GDNF, NGF and BDNF as therapeutic options for neurodegeneration. Pharmacol. Ther. 138, 155–175. doi:10.1016/j.pharmthera.2013.01.004

Altar, C. A., Cai, N., Bliven, T., Juhasz, M., Conner, J. M., Acheson, A. L., et al. (1997). Anterograde transport of brain-derived neurotrophic factor and its role in the brain. Nature 389, 856–860. doi:10.1038/39885

Anderson, A., Oquendo, M. A., Parsey, R. V., Milak, M. S., Campbell, C., and Mann, J. J. (2004). Regional brain responses to serotonin in major depressive disorder. J. Affect. Disord. 82, 411–417. doi:10.1016/j.jad.2004.04.003

Anisman, H., Merali, Z., and Poulte, M. O. (2012). “Gamma-aminobutyric acid involvement in depressive illness interactions with corticotropin-releasing hormone and serotonin,” in The neurobiological Basis of suicide . Frontiers in neuroscience . Editor Y. Dwivedi (Boca Raton (FL): CRC Press/Taylor and Francis ).

Google Scholar

Autry, A. E., and Monteggia, L. M. (2012). Brain-derived neurotrophic factor and neuropsychiatric disorders. Pharmacol. Rev. 64, 238–258. doi:10.1124/pr.111.005108

Baldari, B., Vittorio, S., Sessa, F., Cipolloni, L., Bertozzi, G., Neri, M., et al. (2021). Forensic application of monoclonal anti-human glycophorin A antibody in samples from decomposed bodies to establish vitality of the injuries. A preliminary experimental study. Healthcare 9, 514. doi:10.3390/healthcare9050514

Bartrup, J. T., Moorman, J. M., and Newberry, N. R. (1997). BDNF enhances neuronal growth and synaptic activity in hippocampal cell cultures. NeuroReport 8, 3791–3794. doi:10.1097/00001756-199712010-00027

Beghi, M., Butera, E., Cerri, C. G., Cornaggia, C. M., Febbo, F., Mollica, A., et al. (2021). Suicidal behaviour in older age: a systematic review of risk factors associated to suicide attempts and completed suicides. Neurosci. Biobehav. Rev. 127, 193–211. doi:10.1016/j.neubiorev.2021.04.011

Borba, E. M., Duarte, J. A., Bristot, G., Scotton, E., Camozzato, A. L., and Chaves, M. L. F. (2016). Brain-derived neurotrophic factor serum levels and hippocampal volume in mild cognitive impairment and dementia due to alzheimer disease. Dement. Geriatr. Cogn. Disord. Extra 6, 559–567. doi:10.1159/000450601

CrossRef Full Text | Google Scholar

Brent, D. A., and Melhem, N. (2008). Familial transmission of suicidal behavior. Psychiatric Clin. N. Am. 31, 157–177. doi:10.1016/j.psc.2008.02.001

Brunoni, A. R., Machado-Vieira, R., Zarate, C. A., Vieira, E. L. M., Vanderhasselt, M.-A., Nitsche, M. A., et al. (2014). BDNF plasma levels after antidepressant treatment with sertraline and transcranial direct current stimulation: results from a factorial, randomized, sham-controlled trial. Eur. Neuropsychopharmacol. 24, 1144–1151. doi:10.1016/j.euroneuro.2014.03.006

Castrén, E., and Monteggia, L. M. (2021). Brain-derived neurotrophic factor signaling in depression and antidepressant action. Biol. Psychiatry 90, 128–136. doi:10.1016/j.biopsych.2021.05.008

Chang, B., Gitlin, D., and Patel, R. (2011). The depressed patient and suicidal patient in the emergency department: evidence-based management and treatment strategies. Emerg. Med. Pract. 13 (1–23), 1–24.

PubMed Abstract | Google Scholar

Chao, C. C., and Lee, E. H. Y. (1999). Neuroprotective mechanism of glial cell line-derived neurotrophic factor on dopamine neurons: role of antioxidation. Neuropharmacology 38, 913–916. doi:10.1016/S0028-3908(99)00030-1

Chen, S., Jiang, H., Liu, Y., Hou, Z., Yue, Y., Zhang, Y., et al. (2017). Combined serum levels of multiple proteins in tPA-BDNF pathway may aid the diagnosis of five mental disorders. Sci. Rep. 7, 6871. doi:10.1038/s41598-017-06832-6

Christophersen, N. S., Grønborg, M., Petersen, T. N., Fjord-Larsen, L., Jørgensen, J. R., Juliusson, B., et al. (2007). Midbrain expression of Delta-like 1 homologue is regulated by GDNF and is associated with dopaminergic differentiation. Exp. Neurol. 204, 791–801. doi:10.1016/j.expneurol.2007.01.014

Colla, M., Kronenberg, G., Deuschle, M., Meichel, K., Hagen, T., Bohrer, M., et al. (2007). Hippocampal volume reduction and HPA-system activity in major depression. J. Psychiatric Res. 41, 553–560. doi:10.1016/j.jpsychires.2006.06.011

Conejero, I., Olié, E., Calati, R., Ducasse, D., and Courtet, P. (2018). Psychological pain, depression, and suicide: recent evidences and future directions. Curr. Psychiatry Rep. 20, 33. doi:10.1007/s11920-018-0893-z

datadot (2024). Suicide mortality rate (per 100 000 population). Available at: https://data.who.int/indicators/i/16BBF41 (Accessed February 26, 2024).

De Simone, S., Bosco, M. A., La Russa, R., Vittorio, S., Di Fazio, N., Neri, M., et al. (2022). Suicide and neurotrophin factors: a systematic review of the correlation between BDNF and GDNF and self-killing. Healthcare 11, 78. doi:10.3390/healthcare11010078

Donovan, M. J., Lin, M. I., Wiegn, P., Ringstedt, T., Kraemer, R., Hahn, R., et al. (2000). Brain derived neurotrophic factor is an endothelial cell survival factor required for intramyocardial vessel stabilization. Development 127, 4531–4540. doi:10.1242/dev.127.21.4531

Duarte Azevedo, M., Sander, S., and Tenenbaum, L. (2020). GDNF, A neuron-derived factor upregulated in glial cells during disease. JCM 9, 456. doi:10.3390/jcm9020456

Ducray, A., Krebs, S. H., Schaller, B., Seiler, R. W., Meyer, M., and Widmer, H. R. (2006). GDNF family ligands display distinct action profiles on cultured GABAergic and serotonergic neurons of rat ventral mesencephalon. Brain Res. 1069, 104–112. doi:10.1016/j.brainres.2005.11.056

Dwivedi, Y. (2012). The neurobiological basis of suicide (Boca Raton, FL: Taylor and Francis/CRC Press ), 454.

Dwivedi, Y., Rizavi, H. S., Conley, R. R., Roberts, R. C., Tamminga, C. A., and Pandey, G. N. (2003). Altered gene expression of brain-derived neurotrophic factor and receptor tyrosine kinase B in postmortem brain of suicide subjects. Arch. Gen. Psychiatry 60, 804–815. doi:10.1001/archpsyc.60.8.804

Edelmann, E., Leßmann, V., and Brigadski, T. (2014). Pre- and postsynaptic twists in BDNF secretion and action in synaptic plasticity. Neuropharmacology 76, 610–627. doi:10.1016/j.neuropharm.2013.05.043

Felmingham, K. L., Dobson-Stone, C., Schofield, P. R., Quirk, G. J., and Bryant, R. A. (2013). The brain-derived neurotrophic factor Val66Met polymorphism predicts response to exposure therapy in posttraumatic stress disorder. Biol. Psychiatry 73, 1059–1063. doi:10.1016/j.biopsych.2012.10.033

Fernandes, B. S., Molendijk, M. L., Köhler, C. A., Soares, J. C., Leite, CMGS, Machado-Vieira, R., et al. (2015). Peripheral brain-derived neurotrophic factor (BDNF) as a biomarker in bipolar disorder: a meta-analysis of 52 studies. BMC Med. 13, 289. doi:10.1186/s12916-015-0529-7

Fusar-Poli, L., Aguglia, A., Amerio, A., Orsolini, L., Salvi, V., Serafini, G., et al. (2021). Peripheral BDNF levels in psychiatric patients with and without a history of suicide attempt: a systematic review and meta-analysis. Prog. Neuro-Psychopharmacology Biol. Psychiatry 111, 110342. doi:10.1016/j.pnpbp.2021.110342

Gadad, B. S., Vargas-Medrano, J., Ramos, E. I., Najera, K., Fagan, M., Forero, A., et al. (2021). Altered levels of interleukins and neurotrophic growth factors in mood disorders and suicidality: an analysis from periphery to central nervous system. Transl. Psychiatry 11, 341. doi:10.1038/s41398-021-01452-1

Garcia, R. (2002). Stress, metaplasticity, and antidepressants. Curr. Mol. Med. 2, 629–638. doi:10.2174/1566524023362023

Ginty, D., and Segal, R. A. (2002). Retrograde neurotrophin signaling: Trk-ing along the axon. Curr. Opin. Neurobiol. 12, 268–274. doi:10.1016/S0959-4388(02)00326-4

Girardi, P., and Pompili, M. (2015). Manuale di suicidologia . Ospedaletto, Pisa: Pacini , 749.

Granier, E., and Boulenger, J. P. (2002). Suicidal risk scale. Encephale 28, 29–38.

Guilloux, J.-P., Douillard-Guilloux, G., Kota, R., Wang, X., Gardier, A. M., Martinowich, K., et al. (2012). Molecular evidence for BDNF- and GABA-related dysfunctions in the amygdala of female subjects with major depression. Mol. Psychiatry 17, 1130–1142. doi:10.1038/mp.2011.113

Hamburger, V., Brunso-Bechtold, J., and Yip, J. (1981). Neuronal death in the spinal ganglia of the chick embryo and its reduction by nerve growth factor. J. Neurosci. 1, 60–71. doi:10.1523/JNEUROSCI.01-01-00060.1981

Hefti, F. (1986). Nerve growth factor promotes survival of septal cholinergic neurons after fimbrial transections. J. Neurosci. 6, 2155–2162. doi:10.1523/JNEUROSCI.06-08-02155.1986

Hochstrasser, T., Ullrich, C., Sperner-Unterweger, B., and Humpel, C. (2011). Inflammatory stimuli reduce survival of serotonergic neurons and induce neuronal expression of indoleamine 2,3-dioxygenase in rat dorsal raphe nucleus organotypic brain slices. Neuroscience 184, 128–138. doi:10.1016/j.neuroscience.2011.03.070

Hock, C., Heese, K., Hulette, C., Rosenberg, C., and Otten, U. (2000). Region-specific neurotrophin imbalances in alzheimer disease: decreased levels of brain-derived neurotrophic factor and increased levels of nerve growth factor in Hippocampus and cortical areas. Arch. Neurol. 57, 846–851. doi:10.1001/archneur.57.6.846

Hoxha, E., Lippiello, P., Zurlo, F., Balbo, I., Santamaria, R., Tempia, F., et al. (2018). The emerging role of altered cerebellar synaptic processing in alzheimer’s disease. Front. Aging Neurosci. 10, 396. doi:10.3389/fnagi.2018.00396

Ibáñez, C. F., and Simi, A. (2012). p75 neurotrophin receptor signaling in nervous system injury and degeneration: paradox and opportunity. Trends Neurosci. 35, 431–440. doi:10.1016/j.tins.2012.03.007

Jaumotte, J. D., and Zigmond, M. J. (2014). Comparison of GDF5 and GDNF as neuroprotective factors for postnatal dopamine neurons in ventral mesencephalic cultures. J Neurosci. Res. 92, 1425–1433. doi:10.1002/jnr.23425

Jornada, L. K., Moretti, M., Valvassori, S. S., Ferreira, C. L., Padilha, P. T., Arent, C. O., et al. (2010). Effects of mood stabilizers on hippocampus and amygdala BDNF levels in an animal model of mania induced by ouabain. J. Psychiatric Res. 44, 506–510. doi:10.1016/j.jpsychires.2009.11.002

Kang, H., and Schuman, E. M. (1995). Long-lasting neurotrophin-induced enhancement of synaptic transmission in the adult Hippocampus. Science 267, 1658–1662. doi:10.1126/science.7886457

Kang, H.-J., Kim, J.-M., Lee, J.-Y., Kim, S.-Y., Bae, K.-Y., Kim, S.-W., et al. (2013). BDNF promoter methylation and suicidal behavior in depressive patients. J. Affect. Disord. 151, 679–685. doi:10.1016/j.jad.2013.08.001

Karege, F., Bondolfi, G., Gervasoni, N., Schwald, M., Aubry, J.-M., and Bertschy, G. (2005a). Low Brain-Derived Neurotrophic Factor (BDNF) levels in serum of depressed patients probably results from lowered platelet BDNF release unrelated to platelet reactivity. Biol. Psychiatry 57, 1068–1072. doi:10.1016/j.biopsych.2005.01.008

Karege, F., Perret, G., Bondolfi, G., Schwald, M., Bertschy, G., and Aubry, J.-M. (2002). Decreased serum brain-derived neurotrophic factor levels in major depressed patients. Psychiatry Res. 109, 143–148. doi:10.1016/S0165-1781(02)00005-7

Karege, F., Vaudan, G., Schwald, M., Perroud, N., and La Harpe, R. (2005b). Neurotrophin levels in postmortem brains of suicide victims and the effects of antemortem diagnosis and psychotropic drugs. Mol. Brain Res. 136, 29–37. doi:10.1016/j.molbrainres.2004.12.020

Katoh Semba, R., Wakako, R., Komori, T., Shigemi, H., Miyazaki, N., Ito, H., et al. (2007). Age-related changes in BDNF protein levels in human serum: differences between autism cases and normal controls. Intl J Devlp Neurosci. 25, 367–372. doi:10.1016/j.ijdevneu.2007.07.002

Keller, S., Sarchiapone, M., Zarrilli, F., Videtič, A., Ferraro, A., Carli, V., et al. (2010). Increased BDNF promoter methylation in the wernicke area of suicide subjects. Arch. Gen. Psychiatry 67, 258–267. doi:10.1001/archgenpsychiatry.2010.9

Kim, Y.-K., Lee, H.-P., Won, S.-D., Park, E.-Y., Lee, H.-Y., Lee, B.-H., et al. (2007). Low plasma BDNF is associated with suicidal behavior in major depression. Prog. Neuro-Psychopharmacology Biol. Psychiatry 31, 78–85. doi:10.1016/j.pnpbp.2006.06.024

Kimhy, D., Vakhrusheva, J., Bartels, M. N., Armstrong, H. F., Ballon, J. S., Khan, S., et al. (2015). The impact of aerobic exercise on brain-derived neurotrophic factor and neurocognition in individuals with schizophrenia: a single-blind, randomized clinical trial. SCHBUL 41, 859–868. doi:10.1093/schbul/sbv022

Klein, A. B., Williamson, R., Santini, M. A., Clemmensen, C., Ettrup, A., Rios, M., et al. (2011). Blood BDNF concentrations reflect brain-tissue BDNF levels across species. Int. J. Neuropsychopharm 14, 347–353. doi:10.1017/S1461145710000738

Krug, E. G., Mercy, J. A., Dahlberg, L. L., and Zwi, A. B. (2002). The world report on violence and health. Lancet 360, 1083–1088. doi:10.1016/S0140-6736(02)11133-0

Levi-Montalcini, R. (1987). The nerve growth factor 35 Years later. Science 237, 1154–1162. doi:10.1126/science.3306916

Lima, G. B., Doorduin, J., Klein, H. C., Dierckx, RAJO, Bromberg, E., and De Vries, E. F. J. (2019). Brain-derived neurotrophic factor in brain disorders: focus on neuroinflammation. Mol. Neurobiol. 56, 3295–3312. doi:10.1007/s12035-018-1283-6

Lin, P.-Y., and Tseng, P.-T. (2015). Decreased glial cell line-derived neurotrophic factor levels in patients with depression: a meta-analytic study. J. Psychiatric Res. 63, 20–27. doi:10.1016/j.jpsychires.2015.02.004

Lindholm, J. S. O., and CastrAcn, E. (2014). Mice with altered BDNF signaling as models for mood disorders and antidepressant effects. Front. Behav. Neurosci. 8, 8. doi:10.3389/fnbeh.2014.00143

Maheu, M., Lopez, J. P., Crapper, L., Davoli, M. A., Turecki, G., and Mechawar, N. (2015). MicroRNA regulation of central glial cell line-derived neurotrophic factor (GDNF) signalling in depression. Transl. Psychiatry 5, e511. doi:10.1038/tp.2015.11

Mann, J. J. (2003). Neurobiology of suicidal behaviour. Nat. Rev. Neurosci. 4, 819–828. doi:10.1038/nrn1220

Miao, Z., Wang, Y., and Sun, Z. (2020). The relationships between stress, mental disorders, and epigenetic regulation of BDNF. IJMS 21, 1375. doi:10.3390/ijms21041375

Michel, T. M., Frangou, S., Camara, S., Thiemeyer, D., Jecel, J., Tatschner, T., et al. (2008). Altered glial cell line-derived neurotrophic factor (GDNF) concentrations in the brain of patients with depressive disorder: a comparative post-mortem study. Eur. Psychiatr. 23, 413–420. doi:10.1016/j.eurpsy.2008.06.001

Michel, T. M., Frangou, S., Thiemeyer, D., Camara, S., Jecel, J., Nara, K., et al. (2007). Evidence for oxidative stress in the frontal cortex in patients with recurrent depressive disorder—a postmortem study. Psychiatry Res. 151, 145–150. doi:10.1016/j.psychres.2006.04.013

Middlemas, D. S., Lindberg, R. A., and Hunter, T. (1991). trkB, a neural receptor protein-tyrosine kinase: evidence for a full-length and two truncated receptors. Mol. Cell. Biol. 11, 143–153. doi:10.1128/mcb.11.1.143

Misztak, P., Pańczyszyn-Trzewik, P., Nowak, G., and Sowa-Kućma, M. (2020). Epigenetic marks and their relationship with BDNF in the brain of suicide victims. PLoS ONE 15, e0239335. doi:10.1371/journal.pone.0239335

Molendijk, M. L., Bus, B. A. A., Spinhoven, P., Penninx, BWJH, Kenis, G., Prickaerts, J., et al. (2011). Serum levels of brain-derived neurotrophic factor in major depressive disorder: state–trait issues, clinical features and pharmacological treatment. Mol. Psychiatry 16, 1088–1095. doi:10.1038/mp.2010.98

Neurotrophic (2017). Neurotrophic factors: methods and protocols . New York, NY: Springer Science+Business Media .

Nuernberg, G. L., Aguiar, B., Bristot, G., Fleck, M. P., and Rocha, N. S. (2016). Brain-derived neurotrophic factor increase during treatment in severe mental illness inpatients. Transl. Psychiatry 6, e985. doi:10.1038/tp.2016.227

O Connor, R. C., Platt, S., and Gordon, J. (2011). International handbook of suicide prevention: research, policy and practice . Chichester, West Sussex, U.K: Wiley-Blackwell , 677.

OECD (2012). OECD. Suicide . Paris: OECD . doi:10.1787/9789264183896-10-en

Ojeda, S. R., Hill, D. F., and Katz, K. H. (1991). The genes encoding nerve growth factor and its receptor are expressed in the developing female rat hypothalamus. Mol. Brain Res. 9, 47–55. doi:10.1016/0169-328X(91)90129-L

Otsuki, K., Uchida, S., Watanuki, T., Wakabayashi, Y., Fujimoto, M., Matsubara, T., et al. (2008). Altered expression of neurotrophic factors in patients with major depression. J. Psychiatric Res. 42, 1145–1153. doi:10.1016/j.jpsychires.2008.01.010

Otten, U., Ehrhard, P., and Peck, R. (1989). Nerve growth factor induces growth and differentiation of human B lymphocytes. Proc. Natl. Acad. Sci. U. S. A. 86, 10059–10063. doi:10.1073/pnas.86.24.10059

Pan, W., Banks, W. A., Fasold, M. B., Bluth, J., and Kastin, A. J. (1998). Transport of brain-derived neurotrophic factor across the blood–brain barrier. Neuropharmacology 37, 1553–1561. doi:10.1016/S0028-3908(98)00141-5

Panja, D., and Bramham, C. R. (2014). BDNF mechanisms in late LTP formation: a synthesis and breakdown. Neuropharmacology 76, 664–676. doi:10.1016/j.neuropharm.2013.06.024

Pascual, A., Hidalgo-Figueroa, M., Piruat, J. I., Pintado, C. O., Gómez-Díaz, R., and López-Barneo, J. (2008). Absolute requirement of GDNF for adult catecholaminergic neuron survival. Nat. Neurosci. 11, 755–761. doi:10.1038/nn.2136

Paska, A. V., Zupanc, T., and Pregelj, P. (2013). The role of brain-derived neurotrophic factor in the pathophysiology of suicidal behavior. Psychiatr. Danub 25 (Suppl. 2), S341–S344.

Pitman, A., Krysinska, K., Osborn, D., and King, M. (2012). Suicide in young men. Lancet 379, 2383–2392. doi:10.1016/S0140-6736(12)60731-4

Pruunsild, P., Kazantseva, A., Aid, T., Palm, K., and Timmusk, T. (2007). Dissecting the human BDNF locus: bidirectional transcription, complex splicing, and multiple promoters. Genomics 90, 397–406. doi:10.1016/j.ygeno.2007.05.004

Radka, S. F., Hoist, P. A., Fritsche, M., and Altar, C. A. (1996). Presence of brain-derived neurotrophic factor in brain and human and rat but not mouse serum detected by a sensitive and specific immunoassay. Brain Res. 709, 122–130. doi:10.1016/0006-8993(95)01321-0

Ratta-apha, W., Hishimoto, A., Yoshida, M., Ueno, Y., Asano, M., Shirakawa, O., et al. (2013). Association study of BDNF with completed suicide in the Japanese population. Psychiatry Res. 209, 734–736. doi:10.1016/j.psychres.2013.05.030

Ray, M. T., Shannon Weickert, C., and Webster, M. J. (2014). Decreased BDNF and TrkB mRNA expression in multiple cortical areas of patients with schizophrenia and mood disorders. Transl. Psychiatry 4, e389. doi:10.1038/tp.2014.26

Risk and Protective Factors (2023). Risk and protective factors | suicide prevention . China: CDC . Available at: https://www.cdc.gov/suicide/factors/index.html (Accessed November 7, 2022).

Rosa, A. R., Frey, B. N., Andreazza, A. C., Ceresér, K. M., Cunha, A. B. M., Quevedo, J., et al. (2006). Increased serum glial cell line-derived neurotrophic factor immunocontent during manic and depressive episodes in individuals with bipolar disorder. Neurosci. Lett. 407, 146–150. doi:10.1016/j.neulet.2006.08.026

Salas Magaña, M., Tovilla-Zárate, C. A., González-Castro, T. B., Juárez-Rojop, I. E., López-Narváez, M. L., Rodríguez-Pérez, J. M., et al. (2017). Decrease in brain-derived neurotrophic factor at plasma level but not in serum concentrations in suicide behavior: a systematic review and meta-analysis. Brain Behav. 7, e00706. doi:10.1002/brb3.706

Sartorius, A., Hellweg, R., Litzke, J., Vogt, M., Dormann, C., Vollmayr, B., et al. (2009). Correlations and discrepancies between serum and brain tissue levels of neurotrophins after electroconvulsive treatment in rats. Pharmacopsychiatry 42, 270–276. doi:10.1055/s-0029-1224162

Schneider, E., El Hajj, N., Müller, F., Navarro, B., and Haaf, T. (2015). Epigenetic dysregulation in the prefrontal cortex of suicide completers. Cytogenet Genome Res. 146, 19–27. doi:10.1159/000435778

Serra-Millàs, M. (2016). Are the changes in the peripheral brain-derived neurotrophic factor levels due to platelet activation? WJP 6, 84–101. doi:10.5498/wjp.v6.i1.84

Sharif, M., Noroozian, M., and Hashemian, F. (2021). Do serum GDNF levels correlate with severity of Alzheimer’s disease? Neurol. Sci. 42, 2865–2872. doi:10.1007/s10072-020-04909-1

Shimizu, E., Hashimoto, K., Okamura, N., Koike, K., Komatsu, N., Kumakiri, C., et al. (2003). Alterations of serum levels of brain-derived neurotrophic factor (BDNF) in depressed patients with or without antidepressants. Biol. Psychiatry 54, 70–75. doi:10.1016/S0006-3223(03)00181-1

Skaper, S. D. (2017). Nerve growth factor: a neuroimmune crosstalk mediator for all seasons. Immunology 151, 1–15. doi:10.1111/imm.12717

Sonal, A., and Raghavan, V. (2018). Brain derived neurotrophic factor (BDNF) and suicidal behavior: a review of studies from Asian countries. Asian J. Psychiatry 33, 128–132. doi:10.1016/j.ajp.2018.03.004

Sue, D., Sue, D. W., Sue, D. M., and Sue, S. (2016). Understanding abnormal behavior . Eleventh edition. Australia; Mexico: Cengage Learning , 567.

Suicide in the Province (2022) “Suicide in the Province of Foggia: retrospective study and analysis of the difference between men and women,”, 18. USA: JOMH , 1. doi:10.31083/j.jomh1808166

Sun, J., Kong, L., Wu, F., Wei, Y., Zhu, Y., Yin, Z., et al. (2019). Decreased plasma glial cell line-derived neurotrophic factor level in major depressive disorder is associated with age and clinical severity. J. Affect. Disord. 245, 602–607. doi:10.1016/j.jad.2018.11.068

Takebayashi, M., Hisaoka, K., Nishida, A., Tsuchioka, M., Miyoshi, I., Kozuru, T., et al. (2006). Decreased levels of whole blood glial cell line-derived neurotrophic factor (GDNF) in remitted patients with mood disorders. Int. J. Neuropsychopharm 9, 607–612. doi:10.1017/S1461145705006085

Thoenen, H. (1995). Neurotrophins and neuronal plasticity. Science 270, 593–598. doi:10.1126/science.270.5236.593

Thorpe, L. W., and Perez Polo, J. R. (1987). The influence of nerve growth factor on the in vitro proliferative response of rat spleen lymphocytes. J Neurosci. Res. 18, 134–139. doi:10.1002/jnr.490180120

Thorpe, L. W., Werrbach-Perez, K., and Perez-Polo, J. R. (1987). Effects of nerve growth factor on the expression of interleukin-2 receptors on cultured human lymphocytes. Ann. N. Y. Acad. Sci. 496, 310–311. doi:10.1111/j.1749-6632.1987.tb35781.x

Tokumine, J., Kakinohana, O., Cizkova, D., Smith, D. W., and Marsala, M. (2003). Changes in spinal GDNF, BDNF, and NT-3 expression after transient spinal cord ischemia in the rat. J Neurosci. Res. 74, 552–561. doi:10.1002/jnr.10760

Tripp, A., Oh, H., Guilloux, J.-P., Martinowich, K., Lewis, D. A., and Sibille, E. (2012). Brain-derived neurotrophic factor signaling and subgenual anterior cingulate cortex dysfunction in major depressive disorder. AJP 169, 1194–1202. doi:10.1176/appi.ajp.2012.12020248

University, I. (2021). Department of psychiatry, malatya, Turkey, gonenir erbay L, karlidag R, inonu university, department of psychiatry, malatya, Turkey, oruc M, inonu university, department of forensic medicine, malatya, Turkey, cigremis Y, inonu university, department of medical biology and genetics, malatya, Turkey, celbis O, inonu university, department of forensic medicine, malatya, Turkey. Association of BDNF/trkb and NGF/trka levels in postmortem brain with major depression and suicide. Psychiat Danub 33, 491–498. doi:10.24869/psyd.2021.491

Uzdensky, A., Komandirov, M., Fedorenko, G., and Lobanov, A. (2013). Protection effect of GDNF and neurturin on photosensitized crayfish neurons and glial cells. J. Mol. Neurosci. 49, 480–490. doi:10.1007/s12031-012-9858-6

Van Heeringen, K., and Mann, J. J. (2014). The neurobiology of suicide. Lancet Psychiatry 1, 63–72. doi:10.1016/S2215-0366(14)70220-2

Vichi, M., Ghirini, S., Pompili, M., Erbuto, D., and Siliquini, R. (2019). In rapporto Osservasalute 2018: stato di salute e qualità dell’assistenza nelle regioni italiane . Milano : Prex S.p.A .

Wang, H., Yang, Y., Pei, G., Wang, Z., and Chen, N. (2023). Neurotrophic basis to the pathogenesis of depression and phytotherapy. Front. Pharmacol. 14, 1182666. doi:10.3389/fphar.2023.1182666

Wei, G., Wu, G., and Cao, X. (2000). Dynamic expression of glial cell line-derived neurotrophic factor after cerebral ischemia. NeuroReport 11, 1177–1183. doi:10.1097/00001756-200004270-00007

Yasuda, S., Liang, M.-H., Marinova, Z., Yahyavi, A., and Chuang, D.-M. (2009). The mood stabilizers lithium and valproate selectively activate the promoter IV of brain-derived neurotrophic factor in neurons. Mol. Psychiatry 14, 51–59. doi:10.1038/sj.mp.4002099

Yasuda, T., and Mochizuki, H. (2010). Use of growth factors for the treatment of Parkinson’s disease. Expert Rev. Neurother. 10, 915–924. doi:10.1586/ern.10.55

Yip, P. S., Caine, E., Yousuf, S., Chang, S.-S., Wu, K. C.-C., and Chen, Y.-Y. (2012). Means restriction for suicide prevention. Lancet 379, 2393–2399. doi:10.1016/S0140-6736(12)60521-2

Youssef, M. M., Underwood, M. D., Huang, Y.-Y., Hsiung, S., Liu, Y., Simpson, N. R., et al. (2018). Association of BDNF Val66Met polymorphism and brain BDNF levels with major depression and suicide. Int. J. Neuropsychopharmacol. 21, 528–538. doi:10.1093/ijnp/pyy008

Zai, C. C., Manchia, M., De Luca, V., Tiwari, A. K., Chowdhury, N. I., Zai, G. C., et al. (2012). The brain-derived neurotrophic factor gene in suicidal behaviour: a meta-analysis. Int. J. Neuropsychopharm 15, 1037–1042. doi:10.1017/S1461145711001313

Zeigler-Hill, V., and Shackelford, T. K. (2019). Encyclopedia of personality and individual differences (Cham, Switzerland: Springer ), 1.

Zhao, M., Chen, L., Yang, J., Han, D., Fang, D., Qiu, X., et al. (2018). BDNF Val66Met polymorphism, life stress and depression: a meta-analysis of gene-environment interaction. J. Affect. Disord. 227, 226–235. doi:10.1016/j.jad.2017.10.024

Zheng, Y., Fan, W., Zhang, X., and Dong, E. (2016). Gestational stress induces depressive-like and anxiety-like phenotypes through epigenetic regulation of BDNF expression in offspring hippocampus. Epigenetics 11, 150–162. doi:10.1080/15592294.2016.1146850

Keywords: suicide, neurotrophic factor, immunohistochemistry, BDNF, GDNF

Citation: De Simone S, Alfieri L, Bosco MA, Cantatore S, Carpinteri M, Cipolloni L and Neri M (2024) The forensic aspects of suicide and neurotrophin factors: a research study. Front. Pharmacol. 15:1392832. doi: 10.3389/fphar.2024.1392832

Received: 28 February 2024; Accepted: 26 July 2024; Published: 07 August 2024.

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*Correspondence: Margherita Neri, [email protected]

† These authors have contributed equally to this work and share first authorship

‡ These authors have contributed equally to this work and share last authorship

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