Potential forensic application of DNA methylation to identify individuals in a pair of monozygotic twins

Abstract

In forensics, short tandem repeat (STR) markers are useful in identifying individuals from biological evidence found at crime scenes. However, they cannot be used to distinguish between genetically identical monozygotic (MZ) twins, causing problems in cases with an MZ twin as a suspect. DNA methylation, which occurs at the 5′-position of cytosine in CpG dinucleotides, is a type of genetically programmed DNA modification in mammals. Recent studies have shown that monozygotic twins are epigenetically indistinguishable during the early years of life, but older individuals present significant differences in the overall content and genomic distribution of DNA methylation. Therefore, epigenetic changes such as DNA methylation or histone modifications have a great potential in discriminating between MZ twins. Here, we investigated genome-wide differences in DNA methylation among 12 paired MZ twins, using Illumina’s Human Methylation 450K array. We selected between few dozen to several hundred differentially methylated CpG sites (DMCs) from 480,000 CpG sites for each MZ twin pair. Next, we selected candidates by searching for recurrent DMCs among the 12 MZ twin pairs and as a result, found six recurrent CpG sites (cg00211609, cg26287080, cg01558909, cg21036194, cg01419577, cg04620228). In conclusion, our study suggested that the methylation level at recurrent CpG sites could be a useful biomarker for the identification of individuals in a pair of MZ twins.