“Although monozygotic (MZ) twins share the majority of their genetic makeup, they can be phenotypically discordant on several traits and diseases. DNA methylation is an epigenetic mechanism that can be influenced by genetic, environmental and stochastic events and may have an important impact on individual variability. In this study [the authors] explored epigenetic differences in peripheral blood samples in three MZ twin studies on major depressive disorder (MDD).. … Data originated from three geographical regions: UK, Australia and the Netherlands. Ninety-seven MZ pairs (194 individuals) discordant for MDD were included. … Individually, the studies yielded negative results but when combined, classification of the disease state from blood epigenome alone was possible. Network analysis revealed genes and gene networks that support the inflammation hypothesis of MDD.”
Malki K, Koritskaya E, Harris F, Bryson K, Herbster M, Tosto MG: Epigenetic differences in monozygotic twins discordant for major depressive disorder. Transl. Psychiatry 6(6): e839. doi: 10.1038/tp.2016.101; June 2016.