Academic lab finds NAT method for determining age of crime-scene samples
By John Gever
Here's something you might see on a future episode of "CSI," the hit TV series celebrating forensic science. Researchers at West Virginia University (WVU) (Morgantown, WV) have discovered that RNA analysis could potentially be used to determine the age of biological samples at crime scenes.
Current technology is very good at pinpointing the individual who deposited the sample, but not at determining when. Suspects whose blood or semen link them to a crime scene can claim they had been there at some other time; there's currently no analytical technique that can either confirm or disprove it.
However, preliminary research in Clifton Bishop's forensic science lab at WVU has found via PCR analysis that different types of RNA in fluid samples break down at different rates. In particular, ribosomal RNA (rRNA) deteriorates slower than does messenger RNA. Since the deterioration rates for both RNA species are fairly linear, the analysis of their decomposition states leads straightforwardly to a calculation of when the fluid sample was deposited.
According to the group's paper, scheduled for publication in the journal Forensic Science International, the approach works on blood-stains up to 150 days old and is accurate (at least under laboratory conditions) to within a few days.
There are other experimental methods for determining age of biological samples, but they require far more than the microliter sample which is adequate for the WVU group's approach. These other methods also work only on blood and are strongly affected by environmental conditions. The WVU technique should work on a wider range of biological samples -- Bishop said that, theoretically, fingerprints could be amenable to RNA analysis. The group is still studying the effects of temperature and humidity on RNA decay rates.
That issue will need considerable additional research before the technique can be considered validated for courtroom use. Also needed is a definitive explanation for why rRNA resists breakdown better than mRNA. Bishop's group speculated that rRNA is protected by ribosomal proteins whereas mRNA is relatively naked, but this will require confirmation.
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