Low Copy Number DNA

Picture of DNAIt’s a while since I’ve written about Low Copy Number (LCN) DNA testing, but the news today that – as a result of the Omagh bomb trial – the use of this technique is to be reviewed (see BBC story for details) is welcome.

As I wrote previously, “LCN DNA should only be used cautiously – and only with corroborating evidence”, and as I put it in an article on the dangers of DNA databases and the like, it is highly risky to place your faith in technology always working flawlessly: “As investment goes in, a commercial imperative is involved and as DNA increases its aura of infallibility – will the police (or the public, when the information is ‘conveniently’ leaked?) believe those who say they weren’t at the crime scene even though their DNA was? And how long before corroborative evidence becomes less necessary?” (read the rest of the article here).

0 thoughts on “Low Copy Number DNA

  1. I am a geneticist. I read that the Forensic Science Service will not release the raw data and analytical details from the LCN test. I think this is outrageous. The information would include such things as which DNA segment was being amplified, the precise PCR results (ie which alleles were amplified), the assumptions and statistical methods used in the matching and related analysis, and reflections on such things as allele dropout.Apparently there are ‘commercial/ confidentially’ issuesI’d love to know exactly what the Forensice Science Service does provide?

  2. Thanks for the comment. I’ve not seen that news about the Forensic Science Service myself – can you recall where you saw it?

  3. … sorry, it was a news item from some time ago and I don’t recall the source.If you have concerned constituents perhaps you have the power to find out on their behalf.Key information would be,1. The raw data output from application of the DNA techniques used. These are the patterns of peaks which I’ve seen shown recently on TV and which determine an individuals ‘DNA fingerprint’.For example for the Powerplex system see here.http://www.promega.com/applications/hmnid/productprofiles/pp16/default.htm#(click on the link ‘view figure 1)It would be important for a barrister to see these data for the reason that there can be an element of subjectivity (eg when peaks or small or missing) in the way the patterns are interpreted in arriving at the fingerprint? An accused might expect more than just relying on the FSS interpretation.2. The frequency of the accused’s fingerprint within the database (or databases) which the FSS have access to, together with the sizes of the databases. A perfect fingerprint match between the accused and a scene of crime sample is of much less weight if the fingerprint is not rare in the population as a whole. The FSS have sophisticated software for carrying out statistical analysis and providing such things as match probabilities. However a barrister might wish to recruit experts to carry out their own statistical analysis and it is not certain to me whether this is possible at the moment.Happy New YearOwen

  4. A short comment to the geneticist:For LCN the FSS use the commercially available SGM+ system, so it is easy to determine which loci are amplified. The main difference with standard DNA tehniques is the increased PCR cycle number because of the low template. The numerical designations of the alleles can be made available to the court on request and are routinely given to defence scientists. The statistical methods for calculating match probabilities have been published, are well established and are no different from standard DNA methods. A hard copy of the profile generated (i.e. the pattern of peaks)is kept on file and is also made available to defence scientists. It is this hard copy that the FSS scientist (and most defence scientists) would use in their interpretation of the profile. None of this relates to the “raw data” issue, which appears to be an excuse to have access to an electronic version of the data in order to manipulate it beyond established guidelines and parameters to re-interpret the profile. FSS scientists do not have access to an electronic version of the profile for this very reason.

  5. In regard to low copy number dna what the FSS do not release to the defense is the fact that lcn dna profiles often link more than one person to a crime and they regularly use the one(s) that most fit the needs of the prosecuter and disregard any others as coincidental. This method can easily implicate an innocent person due to the way lcn dna is interpreted. Drop-in, drop-out and random alleles can sometimes be misleading and as lcn dna profiles are almost impossible to reproduce accurately they take an average over 2 samples and disregard what they don’t agree as relevant. Basically they mill ignore evidence in favour of a match.