Distinguishing Between Identical Twins
Blog Jan 16, 2014
DNA Worldwide Group in conjunction with partner Eurofins Forensic, has proven that contrary to previous beliefs that only epigenetic code varied between identical twins, there is also a clear distinction between their base genetic codes.
This crucial breakthrough completely transforms the legal landscape for distinguishing between identical twins for criminal evidence and paternity cases.
We spoke to David Nicholson, DNA Worldwide Group managing director to understand more about this breakthrough and its implications.
AB: How does this research enable the identification of the genetic difference between identical twins?
David Nicholson (DN):We sequenced the whole genome of a pair of twins and a child of one twin using a technology called ultra-deep next generation sequencing. After evaluation of these data using bioinformatics tools, we were able to identify rare mutations that are present only in one twin (and his child) and not in his brother.
AB: What did you do different to previous research, what techniques did you use?
DS: Previous research in this field focused on twin pairs with one twin carrying a genetic disease. As forensic scientists interested in paternity testing, we included the child of one twin and could filter our data for inherited mutations. This gave us a chance to validate our observations directly in the deep next generation sequencing dataset. Furthermore, our sequencing approach used a very high coverage. Typically, deep next generation sequencing
AB: The research has proven contrary to the belief that only epigenetic code varies between identical twins. How long has this belief persisted and what was your driver for the investigating its validity?
DN: There several years now it was believed that identical twins may be distinguishable due to mutations occurring after the split of the embryo, but nobody had proven it so far. Our driver in the beginning was a theoretical paper dealing with this problem (Krawczak et al, How to distinguish genetically between an alleged father and his monozygotic twin: a thought experiment. Forensic Sci Int Genet. 6, 129–130 (2012)). The authors strongly suggest to conduct paternity testing in the context of identical twins by whole genome sequencing to identify rare de novo mutations. However, this was only theoretical. Last year, we were approached by a High German family court dealing with a paternity case involving identical twins as fathers. We offered to sequence the twins, but had to say that no one did this before. The court decided not to request the analysis, mainly because they considered our approach as “experimental”. We therefore decided to make an inhouse test with twin volunteers as a proof of the method.
AB: What do you see as the impact of this research?
DN: Our finding show that identical twins can be genetically distinguished. It is now not only applicable to twin paternity cases, but also to forensic cases stains found at crime scenes. Such cases could not be solved with genetic means in the past, but now we can!
AB: The news story mentioned “a number of high profile cases featuring identical twins where the culprit has been unidentifiable,” is this a common occurrence?
DN: About 6 of 1000 males are identical twins. Therefore, crime or paternity cases with MZ twins are not infrequent and sometimes receive a high level of attention