Abstract: Objective To evaluate the potential usefulness of DNA methylation in individual discrimination of monozygotic twins by investigating the differences of DNA methylation profiles in monozygotic twins’ blood samples. Methods Blood samples from 22 pairs of monozygotic twins were obtained with informed consent. Genomic DNA extracts were bisulfite treated followed by detection with Infinium?誖HumanMethylation27 BeadChip Assays（Illumina, USA）. Epigenetic distances between each pair of monozygotic twins and each pair of unrelated individuals of same gender were calculated with Euclidean distance algorithms. Distribution of epigenetic distance in monozygotic twin group was statistically compared with that in unrelated individuals. Results Difference of epigenetic distance between male and female pairs was not statistically significant in unrelated individual group or in monozygotic twin group（P=0.069 5 and 0.482 5, respectively）. Epigenetic distance of monozygotic twins was significantly lower than that of unrelated individual pair of same gender（Median： 6.02 vs 7.20, P=0.000 2）. However, all the epigenetic distance in monozygotic twin group or in unrelated individuals were significantly higher than 4.00（P<0.000 1）. Conclusion DNA methylation profiles of monozygotic twin’s blood samples were significantly different with each other, which was similar to that in unrelated individuals of same gender. These results indicated that DNA methylation was a useful biomarker in individual discrimination of monozygotic twins.

Key words: forensic genetics, twins, monozygotic, methylation, individual identification