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It’s possible to retrieve forensically relevant information from human DNA in household dust, a new study finds.
After sampling indoor dust from 13 households, researchers were able to detect DNA from household residents over 90% of the time, and DNA from non-occupants 50% of the time. The work could be a way to help investigators find leads in difficult cases.
Specifically, the researchers were able to obtain single nucleotide polymorphisms, or SNPs, from the dust samples. SNPs are sites within the genome that vary between individuals—corresponding to characteristics like eye color—that can give investigators a “snapshot” of the person.
“SNPs are just single sites in the genome that can provide forensically useful information on identity, ancestry, and physical characteristics—it’s the same information used by places like Ancestry.com—that can be done with tests that are widely available,” says Kelly Meiklejohn, assistant professor of forensic science and coordinator of the forensic sciences cluster at North Carolina State University and corresponding author of the study in the Journal of Forensic Sciences.
“Because they’re single sites, they’re easier to recover for highly degraded samples where we may only be able to amplify short regions of the DNA,” Meiklejohn says.
“Traditional DNA analysis in forensics amplifies regions ranging from 100 to 500 base pairs, so for a highly degraded sample the large regions often drop out. SNPs as a whole don’t provide the same level of discrimination as traditional forensic DNA testing, but they could be a starting place in cases without leads.”
Meiklejohn and her team recruited 13 diverse households and took cheek swabs from each occupant along with dust samples from five areas within each home: the top of the refrigerator, inside the bedroom closet, the top frame of the front door, a bookshelf or photo frame in the living room, and a windowsill in the living room.
Utilizing massively parallel sequencing, or MPS, the team was able to quickly sequence multiple samples and target the SNPs of interest. They found that 93% of known household occupants were detected in at least one dust sample from each household. They also saw DNA from non-occupants in over half of the samples collected from each site.
“This data wouldn’t be used like traditional forensic DNA evidence—to link a single individual to a crime—but it could be useful for establishing clues about the ancestry and physical characteristics of individuals at a scene and possibly give investigators leads in cases where there may not be much to go on,” Meiklejohn says.
“But while we know it is possible to detect occupants versus non-occupants, we don’t know how long an individual has to stay in a household before they leave DNA traces in household dust.”
The researchers plan to address the question of how much time it takes for non-occupants to be detected in dust in future studies. Meiklejohn sees the work as being useful in numerous potential investigative scenarios.
“When perpetrators clean crime scenes, dust isn’t something they usually think of,” Meiklejohn says. “This study is our first step into this realm. We could see this being applied to scenarios such as trying to confirm individuals who might have been in a space but left no trace blood, saliva, or hair. Also for cases with no leads, no hit on the national DNA database, could household dust provide leads?”
The NC State College of Veterinary Medicine funded the work. Additional coauthors are from Massachusetts Institute of Technology and NC State.
Source: NC State
The post Household dust harbors forensic DNA info appeared first on Futurity.
A new forensic science study sheds light on how the bones of infants and children decay.
The findings will help forensic scientists determine how long a young person’s remains were at a particular location, as well as which bones are best suited for collecting DNA and other tissue samples that can help identify the deceased.
“Crimes against children are truly awful, and all too common,” says Ann Ross, a professor of biological sciences at North Carolina State University and coauthor of the study in the journal Biology.
“It is important to be able to identify their remains and, when possible, understand what happened to them. However, there is not much research on how the bones of infants and children break down over time. Our work here is a significant contribution that will help the medical legal community bring some closure to these young people and, hopefully, a measure of justice.”
For the study, the researchers used the remains of domestic pigs, which are widely used as an analogue for human remains in forensic research. Specifically, the researchers used the remains of 31 pigs, ranging in size from 1.8 kilograms (4 pounds) to 22.7 kilograms (50 pounds). The smaller remains served as surrogates for infant humans, up to one year old. The larger remains served as surrogates for children between the ages of one and nine.
The surrogate infants were left at an outdoor research site in one of three conditions: placed in a plastic bag, wrapped in a blanket, or fully exposed to the elements. Surrogate juveniles were either left exposed or buried in a shallow grave.
The researchers assessed the remains daily for two years to record decomposition rate and progression. The researchers also collected environmental data, such as temperature and soil moisture, daily.
Following the two years of exposure, the researchers brought the skeletal remains back to the lab. The researchers cut a cross section of bone from each set of remains and conducted a detailed inspection to determine how the structure of the bones had changed at the microscopic level.
The researchers found that all of the bones had degraded, but the degree of the degradation varied depending on the way that the remains were deposited. For example, surrogate infant remains wrapped in plastic degraded at a different rate from surrogate infant remains that were left exposed to the elements. The most significant degradation occurred in juvenile remains that had been buried.
“This is because the bulk of the degradation in the bones that were aboveground was caused by the tissue being broken down by microbes that were already in the body,” says corresponding author and PhD candidate Amanda Hale. “Buried remains were degraded by both internal microbes and by microbes in the soil.”
Hale is a research scientist at SNA International working for the Defense POW/MIA Accounting Agency.
The researchers also used statistical tools that allowed them to better assess the degree of bone degradation that took place at various points in time.
“In practical terms, this is one more tool in our toolbox,” Ross says. “Given available data on temperature, weather, and other environmental factors where the remains were found, we can use the condition of the skeletal remains to develop a rough estimate of when the remains were deposited at the site. And all of this is informed by how the remains were found. For example, whether the remains were buried, wrapped in a plastic tarp, and so on.
“Any circumstance where forensic scientists are asked to work with unidentified juvenile remains is a tragic one. Our hope is that this work will help us better understand what happened to these young people.”
Source: NC State
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