Epigenetic differences arise during the lifetime of monozygotic twins

TLDR

Monozygotic twins share a genotype yet often show phenotypic discordance, likely driven by epigenetic differences. The study aimed to investigate global and locus‑specific DNA methylation and histone acetylation differences in monozygotic twins. The authors examined these epigenetic marks in a large cohort of monozygotic twins. They found that while twins are epigenetically indistinguishable in early life, older twins exhibit marked differences in 5‑methylcytosine and histone acetylation patterns that alter gene expression, underscoring epigenetics’ role in phenotypic divergence.

Abstract

Monozygous twins share a common genotype. However, most monozygotic twin pairs are not identical; several types of phenotypic discordance may be observed, such as differences in susceptibilities to disease and a wide range of anthropomorphic features. There are several possible explanations for these observations, but one is the existence of epigenetic differences. To address this issue, we examined the global and locus-specific differences in DNA methylation and histone acetylation of a large cohort of monozygotic twins. We found that, although twins are epigenetically indistinguishable during the early years of life, older monozygous twins exhibited remarkable differences in their overall content and genomic distribution of 5-methylcytosine DNA and histone acetylation, affecting their gene-expression portrait. These findings indicate how an appreciation of epigenetics is missing from our understanding of how different phenotypes can be originated from the same genotype.