In a move that could make a critical contribution to forensic investigations, scientists have developed a powerful new technique to predict a person's age from a sample of their blood.

Writing in the journal Current Biology, Erasmus MC Medical Centre, Rotterdam, researcher Manfred Kayser and his colleagues demonstrate that it's possible to age a blood donor with a precision of plus or minus nine years by studying the DNA present in the donor's T lymphocytes, which are a type of white blood cell.

Bags of blood collected during donation, showing dark colour of venous blood.The technique makes use of an observation that T cells contain additional small, circular pieces of DNA known as signal joint TCR excision circles - sj TRECS for short.  These are produced when the cells rearrange their DNA in order to mount a targeted immune response and there are usually a large number of them, although, critically, this number declines with age in a predictable fashion.

What the Dutch team do is to quantify the number of sj TRECS and then work out how much DNA is present overall in order to standardise the count.  This enables them to make their prediction of the age of the person who produced the blood, which might be the only sample found at a crime scene.

According to Kayser, this is currently the most accurate ageing method currently available. But where it will really come into its own is that it can be combined with other DNA techniques that can now make predictions as to a person's appearance based on their genetic make-up.  However, knowing roughly how old a victim or perpetrator is can be used to dramatically improve the power of such techniques because more accurate descriptions can be produced.

Commenting on the work, Kayser points out that "conventional DNA profiling applied in forensics can oly identify persons already known to the investigating bodies, because the approach is completely comparative.  Hence, every forensic lab is confronted with cases where the DNA profile obtained from the evidence material does not match that of any known suspect tested, nor anybody in the criminal DNA database, and such cases therefore cannot be solved so far.  In such cases, it is expected that appearance information estimated from evidence material will help in finding unknown persons..."


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