A CONTROVERSIAL DNA test was given the all clear last week by a panel commissioned by the UK government. However, the panel said the test will not be trusted fully until it is validated internationally by independent experts.
Just four or five cells are all that are needed to identify someone through low-template DNA (LTD) analysis, making it potentially extremely useful. Standard DNA fingerprinting, by contrast, works only if there are more than 200 cells in the sample.
Many people have criticised the test for being unreliable, however. For example, in one UK case, a sample of forensic tape carrying tiny amounts of DNA related to a murder inquiry drew a blank when analysed by one company, but a positive result when analysed by another. The technique was also heavily criticised last December by the judge in a trial that acquitted Sean Hoey of planting the 1998 bomb in Omagh, Northern Ireland, which killed 29 people.
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The DNA technique has nevertheless been used to secure convictions in a number of high-profile international murder cases, including that of British backpacker Peter Falconio in the Australian outback in 2001.
鈥淟ow-template DNA analysis has been used to bring convictions in a number of high-profile international murder cases鈥�
It is currently used in New Zealand, the Netherlands, New York state and Switzerland, as well as in the UK where it was pioneered. It has also been used for years by the International Commission on Missing Persons, based in Sarajevo, Bosnia and Herzegovina, to identify the remains of people killed in Rwanda, Kosovo and Serbia, and by the 2004 Indonesian tsunami.
So why the discrepancy between critics and proponents? The UK panel concluded that there are 鈥渢echnical shortcomings鈥� with the test, but that they can be limited. The most serious are so-called allelic 鈥渄rop-outs鈥�, where a specific piece of DNA is missing from the expected fingerprint pattern. Panel member Adrian Linacre of the University of Strathclyde in Glasgow says this results from imperfect amplification of DNA from the tiny sample available and the added complication of having to subject it to up to six more cycles of copying than the usual 28 used for standard DNA fingerprinting. The small sample size also makes contamination during collection a major issue.
In the light of these problems, the panel urged that the protocols behind collection and analysis of samples should be standardised and forensics teams given more training. It also recommended international assessments. 鈥淛ust because the UK does the test and no one else, it doesn鈥檛 mean it鈥檚 a bad test,鈥� says Linacre.
Even allowing for the test鈥檚 limitations, though, the panel said it was satisfied that the three companies offering the test in the UK had adequately validated their techniques, despite the fact that they were all done in-house rather than by peer review. The standard 28-cycle test has been extensively peer-reviewed by independent groups.
