Law-enforcement technologyBlood at crime scene identifies age of perpetrator
New DNA tests of minute amounts of blood left by the perpetrator at a crime scene can now allow police to predict, with a high degree of accuracy, the age of the perpetrator; to be more precise: the test accurately predicts what 20-year age bracket (1-20, 20-40, etc.), from birth to eighty years, the donor of the blood sample belongs to
This is good news for law enforcement: blood left at a crime scene could be used to estimate the age of a perpetrator, thanks to a new DNA test. The test could narrow down the range of possible suspects.
Manfred Kayser at the Erasmus University Medical Centre in Rotterdam, the Netherlands, and colleagues say their test needs between 5 and 50 nanograms of DNA to predict someone’s age to within twenty years. This can normally be retrieved from a small drop of blood.
Miriam Frankel writes that the researchers took blood samples from 195 individuals whose ages ranged from a few weeks to eighty years. After extracting DNA from the sample, they amplified it using the polymerase chain reaction to generate billions of copies of DNA fragments called sjTRECs, or “signal joint T-cell receptor rearrangement excision circles.” These fragments are produced as by-products when the receptors of infection-fighting T-cells rearrange themselves to become more diverse and better at combating foreign agents in the blood by deleting pieces of their DNA. People are known to have fewer sjTRECs as they age.
Kayser, writing in Current Biology, says that after the assessing the sjTREC level in each sample and comparing it with the donor’s age, he can accurately predict what 20-year age bracket, from birth to eighty years, the blood sample belongs to.
Kayser says this method is more accurate than previous DNA-based age tests, such as those that analyze mitochondrial DNA deletions, which cannot detect ages below twenty years old. Other methods also need more intact DNA.
The team also found that the technique works on blood samples up to eighteen months old. If, as they hope, it is accurate for even older samples, it could be useful for solving past crime cases where blood was collected.
As it stands, the test has its limitations, says Peter Gill, a former principal research scientist at the Forensic Science Service in the United Kingdom. “Although this test is a useful thing to have in the armory, it would be a lot more practical if the age brackets could be narrowed down to about five years,” he says.
— Read more in D. Zubakov et al., “Estimating human age from T-cell DNA rearrangements,” Current Biology 20, no. 22, R970-R971 (23 November 2010) (doi:10.1016/j.cub.2010.10.022) (sub. req.)
