How useful is sequencing for forensics?

Between 2007 and 2009 police in Germany were frantically looking for a criminal. Although her identity was not known, it was clear that she was dangerous: DNA evidence from 40 crime scenes, including several murder scenes, could be linked to her.

Despite immense efforts lasting more than two years, they did not succeed. Eventually, they had to admit that the reason why they had found DNA from the same woman in all those crime scenes was that the cotton swabs used in the investigation were all contaminated by the same cotton swab factory worker.

This episode of forensic history illustrates how much law enforcement has come to rely on DNA evidence. The centrepiece of this effort are national DNA databases, which have acronyms like CODIS (USA), NDNAD (UK), or  FNAEG (France). Each of those databases contains millions of unique DNA profiles.

Whilst DNA is central to modern forensics, DNA sequencing is not: The profiles in the databases are obtained using capillary electrophoresis of polymorphic loci called VNTRs. Is this likely to change with the arrival of more affordable sequencers?

 

Arthur Eisenberg, who established one of the world's first forensics labs, thinks so. In a recent interview published on Genomeweb, he envisages a future where all forensic DNA testing is done using sequencing.

More widespread use of sequencing in forensics could have a number of benefits. Firstly, sequencing would return information on DNA polymorphisms other than just VNTRs. This includes SNPs, which are much more common than VNTRs. SNPs are informative of traits like eye colour, hair colour, and race, and could be used for facial composites(although this would not be legal in some countries, including Germany).

Another advantage of sequencing is that it can be applied to a wider range of forensic samples than VNTR profiling. Shed hair is recovered from a lot of crime scenes, but cannot be analysed using VNTR profiling because it usually does not contain nuclear DNA. It does however contain mitochondrial DNA, which is already used for forensic investigations.

A major challenge for sequencing is backwards compatibility. Existing VNTR-based forensic databases already have millions of entries, which are not easily comparable to the output of most next generation sequencing (NGS) machines. The reason is that NGS sequencers can typically only read 100-200 bases at a time, whilst for gaining reliable information on VNTRs read lengths of 400 bases or more are required. This is likely to become less of a problem in the next few years, as read lengths increase.

Another remaining challenge is that NGS is not sufficiently reproducible to be admitted as evidence in a court of law. The same barrier exists for the widespread adoption of NGS in the clinic, where reproducibility is essential as well, but cannot yet be demonstrated for NGS-based tests either.

In summary, the hurdles for the widespread adoption of DNA sequencing in forensics seem to be technical, and solvable.

If you have a view on whether sequencing has a future in forensics, please do not hesitate to post your comment below.