How a strand of hair might identify a criminal

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Your own combination of hair proteins could pick you out of a million people – but don’t expect the technique to become as widespread as DNA testing for a long time (if at all).
Credit: Lisa Marie Thompson / Getty Images

There is little doubt that DNA profiling has revolutionised criminal justice systems and archaeological research. But could there be a better method for determining human identity? 

A study by a US team in the journal PLOS One suggests there is – your hair.

DNA samples from, say, skin cells often degrade by exposure to factors such as bacteria, fungi, ultraviolet light and weathering.

This sort of damage can limit scientists’ ability to distinguish genetic variations within a sample, essentially rendering it useless. And in this event, there are few viable alternatives for investigators.

So Parker and his team claim there is a fundamental need for the development of human identification technology that does not rely on DNA analysis alone.

They argue that since hair proteins can persist for longer periods of time, analysis based on them would make an excellent supplement to DNA profiling and boost current methods of personal identification significantly.

To qualify the potential of protein analysis, Parker and his colleagues examined the human hair shaft proteome – the group of proteins inside the part of the hair that extends beyond the skin.

Human hair retains a high protein content after it falls out; more than 300 different types have been detected in the hair shaft proteome. Parker and his colleagues note that this makes it a good material for them to attempt to discern identity from.

So Parker and his colleagues examined samples of hair from 66 people of European-American origin and 10 of African descent, along with six archaeological hair samples up to 260 years old.

From this group, the researchers discovered a total of 185 different hair protein markers.

They suggest that this would be enough to provide a unique signature that could be used to identify one person in a million.

The team aims to eventually establish a core set of 100 protein markers, with which they could identify anyone in the world from a single strand of hair.

Study co-author Brad Hart from the Lawrence Livermore National Laboratory says while the work is still in its early day, its impact could be enormous.

“We are in a very similar place with protein-based identification to where DNA profiling was during the early days of its development,” he says.

Peter Gunn, a forensic biologist at the University of Technology Sydney in Australia, on the other hand, says that this conclusion is significantly exaggerated.

Gunn has been involved in DNA testing in Australia since 1988 and was one of the first to conduct start-to-finish DNA testing for a criminal matter in the southern hemisphere.

He claims that there is not nearly as much need for the proteome method as the authors of this study indicated.

“I would see the application of this as extremely limited in a practical operation,” he says.

“We are [currently] getting results from maybe 10 to 20 picograms of DNA, which is maybe half a dozen cells’ worth of DNA.”

Gunn also claims that the study’s sample group is far too narrow.

“They have been very selective about what they have looked at,” he explains.

“They have eliminated anyone who may have had mixed ancestry [and] they’ve eliminated some protein variations or some amino acid variations that could be a bit ambiguous.”

Gunn did suggest that there could be some limited applications of this work in ancestral studies.

But first, scientists would need hundreds or even thousands of more samples from a wider variety of people than the few groups examined in Parker and his colleagues’ study.

For now, at least, DNA profiling remains the undisputed king of personal identification methods.

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