Identical twins on trial: can DNA testing tell them apart?

"When DNA is found at a crime scene, forensic scientists typically attempt to identify the person it belongs to using a technique called short tandem repeat (STR) analysis. The technique uses the polymerase chain reaction (PCR) method to amplify up to 30 specific regions of the genome that have a lot of genetic variation. These amplified regions are sequenced to determine the number of STRs and their base pair patterns, which can then be compared to genealogy databases or STR profiles of suspects to identify any potential matches."

"Whole-genome sequencing can make it possible to tell identical twins apart. By analysing the entirety of a person's genome, scientists can identify differences caused by mutations that occurred after an egg split. These changes are rare. For instance, a 2014 study identified just five genetic changes between a pair of adult twins."

"There have been rare cases in which sequencing of the entire genome has helped courts to distinguish between twins. But using whole-genome sequencing requires sufficient amount of DNA to analyse."

Standard forensic DNA testing using short tandem repeat (STR) analysis cannot differentiate between monozygotic twins because they possess identical DNA sequences in the regions typically analyzed. STR analysis amplifies and sequences up to 30 specific genome regions with high genetic variation, which normally allows easy identification of individuals. However, identical twins resulting from a single fertilized egg splitting have no differences in these regions. Whole-genome sequencing offers a potential solution by identifying rare mutations that occurred after the egg split, though such genetic changes are uncommon. Courts have occasionally used whole-genome sequencing to distinguish between twins, but this approach requires sufficient DNA material for analysis.

Read at Nature