A Little Dab Will Do Ya (In)
ONE DROP OF BLOOD may be enough to provide an age range of a crime suspect or victim, based on a new DNA testing method developed by researchers in the Netherlands.
All that is necessary is a small amount of blood, according to the researchers. The test, known as an assay, works as follows: T-cells (so called because they develop in the thymus, an organ above the heart) employ T-cell receptors to recognize foreign invaders in the body so that the T-cells can kill them. The T-cells must undergo rearrangements to develop those receptors, creating some byproducts known as sjTRECs, which appear in the blood as circles. SjTREC presence in blood tends to decrease as age increases.
The researchers took blood samples from 195 subjects ranging in age from a few weeks through 80 years and determined that age ranges could be estimated based on the number of sjTREC circles in the blood.
That could be a boon to crime scene investigators. As Manfred Kayser, a researcher on the project, head of the Department of Forensic Molecular Biology at Erasmus University Medical Center in Rotterdam, explains, traditional methods of age detection involve looking at skeletons or teeth, but those are not always found as evidence at a crime scene.
“You are left with quite a number of crime cases where you don’t have bones and you don’t have teeth, and therefore, you usually cannot apply those conventional methods of age estimation,” he says. “But you may just have blood in many of the violent crimes.”
This method is different from typical DNA tests, which compare DNA found at crime scenes or taken from suspects with DNA files on record. In those cases, if there is no match on file, the DNA won’t provide the answers without more specific tests. With the sjTREC method, an age range can at least be produced even if a suspect’s DNA is not in the criminal justice system databases already.
Blood holds up better than various other types of age indicators, such as mitochondria, says David Wiest, an immunologist and deputy scientific director at Fox Chase Cancer Research Center. “It has advantages in that other types of indicators of age tend to degrade over time, whereas the DNA won’t. It’s much more stable,” says Wiest.
The test can only make a prediction within a range of about 20 years, however, and the true measure of uncertainty can be as much as 35 years. “There are also some requests I have received since we published the paper…where some lawyers had contacted me, ‘Can I say that the person is 43 instead of 41,’ or something. Of course, this is impossible with the current technology,” says Kayser.
Even such a broad age-range estimate could be useful if blood is the only evidence at the scene of the crime. But investigators must balance these findings with the knowledge that environmental or biological factors other than age can affect the output of T-cells from the thymus, says Wiest. If a person has cancer and is treated with chemotherapy, for example, that would affect the thymus’s output and thus, fewer sjTREC circles would be visible. Additionally, stress and other factors affect output, says Wiest.