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Dutch scientists have developed a technique that would make it possible to use blood collected at crime scenes to estimate the age of a suspect or missing person.

In a report published today in Current Biology, researchers argue that law enforcement agencies could start using their findings immediately. They say that they have already begun work to validate the method, to ensure that it meets quality standards.

Professor Manfred Kayser of the Erasmus MC University Medical Center, Rotterdam, says the method would be useful on crime scenes where bloodstains are the only forensic evidence.

"We demonstrate that human age can be estimated from blood with reasonable accuracy, using a simple robust and sensitive test assay", he says.
T cells key to blood puzzle

The method relies on a trademark characteristic of T cells, the cells in our blood which defend us against invading bacteria, viruses and parasites, as well as mutating cells such as those found in tumours and cancers.

T cells can create a diverse range of receptors to recognise these nasties, via a specific rearrangement of their DNA. As a by-product of that process they create small circular DNA molecules known as signal joint TCR excision circles, or sjTRECS for short. The number of sjTRECS molecules in the blood declines at a constant rate with age.

Kayser says the number of these molecules in a blood sample are counted against a reference gene not affected by age, which allows them to calculate the total amount of DNA in the sample.

The method allows an estimate of age with an error range of approximately nine years either way, Kayser says. The study suggests the test would be highly accurate in placing unknown persons into generational categories spanning about twenty years.
Pushing forensic limits

Professor Claude Roux, director of forensic studies at the University of Technology, Sydney, says it's an interesting piece of research by Kayser, who is a world leader in the field of forensic DNA.

"It's really pretty much cutting edge research. Trying to expand the use of DNA [and] go a bit beyond what's normally done," he says.

Roux says that until now DNA evidence has always had one important limiting factor.

"Biological evidence, and DNA in particular, is very powerful to identify people as long as you have some comparison material," he says.

"[Currently] if you're in a situation where you've got a crime scene and a few blood stains, you are completely in the dark. If you have no comparison material - the offender [or victim] is not in the DNA database - DNA is pretty much hopeless.

"So the general idea here would be to see what is possible to do with the biological material ... get some physical traits of a person, in this case an approximate age."

Roux says at the moment the technique would have limited use, but could be useful when combined with more 'traditional' forensic methods.

"In terms of reliability, I think this needs a fair bit of work before it can be used in case work," he says. "[But] there are cases where it would be helpful to be able to say the person is about fifty years old rather than twenty, where that could direct the investigation quite clearly."

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