Low copy number

Low Copy Number (LCN) is a DNA profiling technique developed by the UK Forensic Science Service (FSS) which has been in use since 1999.

In the United Kingdom use of the technique was suspended between 21 December 2007 and 14 January 2008 while the Crown Prosecution Service conducted a review into its use - this suspension has now been lifted.[1]

LCN is an extension of Second Generation Multiplex Plus (SGM Plus) profiling technique. It is a more sensitive technique because it involves a greater amount of copying via polymerase chain reaction (PCR) from a smaller amount of starting material, meaning that a profile can be obtained from only a few cells, which may be as small as a millionth the size of a grain of salt, and amount to just a few cells of skin or sweat left from a fingerprint.[2]

Advantages

LCN evidence has allowed convictions to be made in several cold cases. For example, Mark Henson was convicted of rape in 2005, 10 years after the crime was committed, from re-analysis of a microscope slide.[3] In 1981, evidence was deliberately kept after the rape and murder of 14-year-old Marion Crofts. In 1999, a DNA profile was obtained from this using LCN. This was continually checked against the UK National DNA Database for the next two years, until a match was eventually found for Tony Jasinskyj after he was arrested for another crime. He was eventually given a life sentence in 2002.[4]

So far the technique is only used in several countries:the UK, the Netherlands and New Zealand.(Citation: NATURE|Vol 464|18 March 2010)

Criticism

It has been used in more than 21,000 serious crime cases in the UK and internationally, particularly in "cold" cases. A FSS spokesman said: "LCN DNA analysis is only carried out by the most-experienced DNA scientists, who have undergone special additional training and testing in this area of casework."[5] However, the technique came under attack from the Judge during the trial of Sean Hoey - who was eventually cleared of involvement in the Omagh Bombing. One of the criticisms the judge leveled at LCN was that although the FSS had internally validated and published scientific papers on the technique, there was an alleged lack of external validation by the wider scientific community.[6] Following the Judge's ruling, the use of the technique was suspended in the UK, pending a review by the Crown Prosecution Service. This review was completed and the suspension lifted on the January 14, 2008 with the CPS stating that it had not seen anything to suggest that any current problems exist with LCN".[1]

The increased sensitivity of LCN also increases the risks posed by contamination of samples in the laboratory. Since LCN aims to amplify levels of DNA as low as 100 picograms, even breathing on a sample may contaminate it substantially enough to render the final profile unusable . Contamination is particularly problematic before the sample has undergone amplification because both the suspect's and the contaminator's DNA will be amplified, resulting in a mixed profile. Moreover, the small amounts of DNA that LCN aims to amplify also increase the probability of PCR artifacts appearing on profiles such as stochastic effects.

Notes

  1. 1 2 CPS Press Release : Review of the use of Low Copy Number DNA analysis in current cases: CPS statement
  2. ↑ DNA test halted after Omagh case, BBC
  3. ↑ THE FORENSIC SCIENCE SERVICE, Fact sheet (6), Cold cases, (PDF)
  4. ↑ Marion Crofts, FSS
  5. ↑ Police suspend use of discredited DNA test after Omagh acquittal
  6. ↑ Judgment in full: the Queen v Sean Hoey - Times Online

References

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