Scientists at the University of Huddersfield in the United Kingdom have discovered a new way to identify differences in the genetic profiles of identical twins.
Dr. Graham Williams and colleagues at the university's Forensic Genetics Research Group developed a method called "high resolution melt curve analysis," or HRMA — designed to locate distinct features in DNA structure.
The main idea behind the method is that gene mutations are affected by lifestyle and environment. Such differences between identical twins could occur if one twin smokes and the other does not, or if one of them has frequent exposure to sunlight and the other twin stays mostly indoors. The researchers believe that these changes can be used to identify one DNA sample from another.
"What HRMA does is to subject the DNA to increasingly high temperatures until the hydrogen bonds break, known as the melting temperature," Dr. Williams said. "The more hydrogen bonds that are present in the DNA, the higher the temperature required to melt them."
Williams added that this method can also help differentiate the DNA between young twins and adult twins, which was very difficult to do before. He, however, pointed out that HRMA is very expensive, and it requires a number of high quality DNA samples that might not be easily available at a crime scene.
"Nevertheless, we have demonstrated substantial progress towards a relatively cheap and quick test for differentiating between identical twins in forensic case work," Dr. Williams said.
The researchers hope that their study can lead to more efficient DNA profiling to identify individuals using crime scene stains.
In 2012, French police investigated a series of rape cases in Marseille, in which most of the evidence pointed toward two potential suspects: identical twins Elwin and Yohan. The victims recognized the twins but could not say which of the two had assaulted them.
"It is a highly unusual affair," said Emmanual Kiehl, the chief of Marseille police, at the time. "This pair [has] almost identical genetic codes. It is possible to tell them apart but... we do not have the facilities here in Marseille."
The instances of rape or sexual violence that involve a twin are "more frequent than we expected," said Georg Gradl a genomic research specialist at the Eurofins laboratory based in Ebersberg, Germany. As of last year, Eurofins has been asked by forensic institutes and police to help solve around 10 different cases involving a twin.
This study was published in the journal Analytical Biochemistry.
Photo: Donnie Ray Jones | Flickr
