Figure 1
From: Epigenetics of discordant monozygotic twins: implications for disease
Shared and non-shared potential epigenetic confounding factors throughout the lifetime of MZ twins and unrelated individuals. MZ twins, in contrast with unrelated individuals, share most genetic variants, as well as similar prenatal and early-life environments. The in utero environment is also shared by MZ twins, although to different degrees: they can have a shared placenta and amnion (monochorionic monoamniotic, left picture), a shared placenta but different amnion (monochorionic diamniotic, middle), or a different placenta and amnion (dichorionic diamniotic, right). Epigenetic studies using MZ twins allow the control of most genetic, maternal, environmental, and cohort effects.