Epigenetics as the Underlying Mechanism for Monozygotic Twin Discordance

Monozygotic twins share an identical DNA sequence but typically display some level of phenotypic discordance. The cause of this discordance is often unknown. Two known contributing factors to phenotype are genetics and environment. While the mechanism for the genetic effect is defined through DNA sequence, the mechanism for expression of the environmental effect is less defined. With the emergence of the field of epigenetics, researchers have begun to consider it an important contributing factor to phenotype. Exposure to various environmental factors has been shown to have an effect on an individual's epigenetic marks and may be the primary mechanism for how the environment induces a change in phenotype. Current research indicates that epigenetic differences between monozygotic twins may be an important contributing factor to phenotypic discordance. Monozygotic twins are an ideal resource for the study of epigenetics since many confounding factors found in the general population, such as variation in DNA sequence, can be eliminated. Uncovering these epigenetic factors will increase our understanding of the molecular mechanisms that may contribute to phenotypic discordance in monozygotic twins and may lead to new theoretical and experimental opportunities in health and disease.