A strand of hair at a crime scene, or clinging to human remains unearthed by archaeologists, could hold new promise as a means to identify its unique owner and unravel mysteries sealed by the passage of time.
In research published this week, scientists from Lawrence Livermore National Laboratories reported they are devising a test of human hair that could fingerprint its owner in cases in which DNA evidence is fragmented, damaged or nowhere to be found. Like DNA sequencing, the test they have devised not only could identify an individual but trace his or her ancestry.
The researchers' discovery, reported Wednesday in the journal PLoS One, addresses one of forensic scientists' most pressing needs: a reliable alternative to DNA identification. DNA is actually quite fragile and notoriously vulnerable to degradation with time and exposure to the environment. It's tricky to coax a full sequence from an old biological sample or one that's been buried, frozen or baked in the sun.
While a shaft of hair often is presented as evidence in an old-fashioned whodunit, it does not actually contain nuclear DNA, the chemical blueprint an individual inherits from both parents. It does contain mitochondrial DNA, but because that is passed down matrilineally, it has limits as a means of identification.
In quainter times, investigators might put a hair under a microscope and compare it to, say, that of a defendant. But in current forensic science, a seeming match under the microscope would not be accepted as proof that two different shafts of hair came from the same person.
Every strand of hair is made up of proteins. In addition to being more resilient to environmental damage than DNA, those proteins are like an echo of a person's DNA, said Brad Hart, co-author of a paper and director of Livermore's Forensic Science Center.
It's a simple but ingenious idea, conceived in 2013 by the paper's lead author, Glendon Parker, then a biochemistry professor at Utah Valley University and now a scientist at Livermore: DNA provides the blueprint for proteins. So the coding quirks found in an individual's DNA (called single nucleotide polymorphisms, or SNPs) will translate into recognizable variants in the proteins, known as single amino acid polymorphisms (SAPs).
These SAPs are the protein markers that could guide future forensic scientists in identifying an individual even when DNA is not available. While they can be found in a single strand of hair, they also can be found in shed skin cells, bones and teeth.
In an effort to discern how specific SNPs became recognizable SAPs, researchers from seven universities collected and analyzed male and female hair samples from 82 people of varying ethnicities.
In the hair samples of 66 European-Americans, five African Americans, five Kenyans and six skeletal remains from the 1750s and 1850s, they identified 185 protein markers that could collectively be used to tell one person from another.
Each person's number of hair protein markers, combined with his or her pattern of protein markers, is unique, researchers found. The authors of the report suggest that as many as 1,000 protein markers could be used to identify individuals and distinguish one person from another. But they are aiming to winnow those to a battery of 90 to 100 protein markers, which could be used to pick one individual out of a worldwide population.
Currently, it takes about two-and-a-half days to prepare a sample and sequence and analyze its proteins. Its cost, say the authors, likely will be competitive with other forensic tests.
"The discovery phase has been quite complex, but once the technique is established, we believe it can be made into a routine procedure for use in crime labs," said Deon Anex, one of the paper's co-authors.
"We really see our job as providing tools for the forensic toolkit," which has been faulted in recent years for its reliance on methodologies considered to be subjective, Hart said. When DNA is not available, he said, looking for its echo in hair proteins is a clever way to glean its missing secrets.
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