lunes, 29 de noviembre de 2010

Crime scene blood could identify age of criminal

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 20 years. This can normally be retrieved from a small drop of blood.
The researchers took blood samples from 195 individuals whose ages ranged from a few weeks to 80 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.
After the assessing the sjTREC level in each sample and comparing it with the donor's age, Kayser says he can accurately predict what 20-year age bracket, from birth to 80 years, a new blood sample belongs to (Current Biology, DOI: 10.1016/j.cub.2010.10.022).
Kayser says this method is more accurate than previous DNA-based age tests, such as those that analyse mitochondrial DNA deletions, which cannot detect ages below 20 years old. Other methods also need more intact DNA.
The team also found that the technique works on blood samples up to 18 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.
The technique works on blood up to 18 months old, and may be accurate for even older samples
As it stands, the test has its limitations, says Peter Gill, a former principal research scientist at the Forensic Science Service in the UK. "Although this test is a useful thing to have in the armoury, it would be a lot more practical if the age brackets could be narrowed down to about five years," he says.

**Published in "New Scientist"