February 11, 2013

Crime and twins

Twins' DNA hinders France sexual assault investigation
Police who are investigating a series of sexual assaults in the southern French city of Marseille have arrested identical twin brothers.

The 24-year-old unemployed delivery drivers, named locally as Elwin and Yohan, were placed under investigation on Friday.

Officers say they are sure that one of the two men carried out the attacks, but that they do not know which.

Standard DNA tests are unable to differentiate between their DNA.


Police have been told it would cost upwards of 1m euros (£850,000) to conduct an ultra-sophisticated genetic test that would be able to tell one set of the twins' DNA from the other.

One expert told the French newspaper La Provence: "For a normal analysis, we would compare 400 base pairs [of nucleotides] which make up DNA."

In the case of identical twins, he added, "We would be looking at billions."
I wonder what is the ultra-sophisticated genetic test they are referring to; presumably no genetic test can be any more sophisticated than a whole genome sequence at very high coverage, and that does not cost a million euros anymore.

The closest I could find on the topic of twin genetic similarity is the following reporting on an ASHG 2012 abstract:

They then calculated the frequency with which these mutations occurred. Only two sets of twins had such mutations, which translates to a DNA change occurring once for every 10 million to 10 billion bases that are copied every time a cell divides. While that may seem like a high accuracy rate, cells in the body divide trillions of times. So that would mean an average twin pair carries 359 genetic differences that occurred early in development. 
One limitation of the study is that they could only estimate the mutation rate based on blood cells, but some cells in the body divide much more frequently and so may rack up many more mutations. Other cells, like brain cells, don't regenerate much and would probably remain stable.


Brad said...

People who understand genetics would know who was guilty from 3 high (or probably even medium) coverage sequencings (you'd need 3 tests, 1 for the sample, and 1 for each brother) would establish guilt and innocence. However this must pay for government labs, government regulations, lawyers, courts, etc. Government does nothing efficiently, and with technology, everything costs 10 times as much.

Dienekes said...

Presumably there may be very little genetic material of the perpetrator to work with, so getting a high coverage genome of that might be difficult and might require techniques similar to those used in ancient DNA research to avoid/remove contamination. Still, 1 million seems excessive to me.

robinryder said...

There is also the possibility that both twins are guilty of the same rape, or that some rapes were committed by one brother and the other rapes by the other brother. To establish this, they would need whole-genome sampling for several samples from the victims.

Aaron said...

Deep sequence the twins to reliably identify divergent SNPs between the brothers and then design primers for PCR amplification of a few select divergent SNPs in the sample with limited genetic material. Problem solved for way less than a million dollars.

andrew said...

Colorado recently had a similar case involving a murder of one of their wives a little less than ten years ago that was resolved in January. Ultimately one brother confessed to the killing and was sentenced to 72 to 75 years with no possibility of parole for 27 years (second degree murder) and the other who watched the murder committed and covered it up was sentenced to 12 years in prison with a possibility of parole after about eight years. This was more lenient that the life without parole sentence that both of them could have been determined by a jury to have deserved if it had found that they conspired with premeditation to jointly commit first degree murder.

Gabriella Kadar said...

Mental illness has a high concordance in identical twins. Like some think, possibly both were involved in the action especially if they were co-habiting. It's a bit of legal nightmare. Almost like the judgement of Solomon: put them both in jail together. If they live together then even if only one was actually raping women, the other knew about it and was hiding the information. They'd probably be lonely alone anyway.