New Forensic Method Can Determine a Person's Age from Blood Left at a Crime Scene

By Clay Dillow Posted 11.22.2010 at 1:08 pm 2 Comments

Estimating Age from the DNA in Blood By adding up the number of a certain kind of DNA molecule present in a blood sample, forensics experts can get a rough estimate of the owner's age. The technique could be used to help build profiles of suspected persons in criminal investigations.

Forensic scientists have a new tool to help them reconstruct the identities of persons at the scene of crime, at least the kind of crime scene where things got physical. Dutch researchers have devised a method for estimating the age of a suspect or missing person by simply examining blood collected from the scene, even if that blood isn’t particularly fresh.

The test isn’t perfect; that is, it has a margin of error of nine years in either direction. But in cases where police are trying to build a profile of an unknown person, the test can narrow the possibilities down to a generational cohort spanning about two decades. Previous attempts to do so have proved inaccurate, but this attempt at deriving a phenotypic human trait from DNA information is at least as accurate, if not more so, than other profiling methods like a similar means of determining eye color from DNA.

The science turns on a certain molecular process tied to the T cells in blood. The ability of T cells to recognize foreign threats depends upon the diversity of receptors that match up with characteristics found in the invaders. That diversity is achieved by a rearrangement of the T cells’ DNA over time, a process that produces distinguishable circular DNA molecules as a byproduct. Those molecules decline constantly in number over time in correlation with the person’s age.

By counting up the number of these circular DNA molecules in a sample and comparing it to the quantity of another reference gene that remains constant throughout a person’s lifetime (as a reference that compensates for the varying amount of DNA in a given sample), forensics experts can deduce, with reasonable accuracy, the age of the blood’s owner.

The method won’t be used like DNA matching that links a suspect definitively to the scene of a crime, but in situations where authorities have no leads regarding the identity of a wanted or missing person, it should help police build a more accurate profile of who it is they are looking for.

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2 Comments

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IceMetalPunk

11/22/10 at 1:39 pm

Cool. T-Cell plasmids are finding some forensic use.

While we're trying to build profiles from the DNA in blood, wouldn't race be an easy phenotype to discern? I'd think there'd be many distinct genetic markers that can be used to determine the race of the owner of a given sample of DNA, right? So being able to identify that would turn the Wanted posters from "Male, 18-36" into "Caucasian Male, 18-36" or something. It would narrow it down even more.

Things like eye color are difficult to determine from DNA because there are many genes that code for it, but not quite so many as to be obvious. Race, on the other hand, surpasses that limit.

-IMP ;) :)

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