Epigenetic Basis of Twin Discordance in Diseases: Future Benefits

Abstract

Monozygotic twins share the same genotype since they are derived from the same zygote. However, monozygotic (MZ) twin siblings frequently present many phenotypic differences, such as their susceptibilities to diseases. These isogenic individuals are not entirely identical. They exhibit phenotypic incompatibility for many features, from birth weight to complex diseases. Recently, several studies have been published showing that phenotypic differences, especially in MZ twins, are being induced from prenatal period to life-long epigenetic differences. Epigenetic studies on twins have a great potential to contribute to our understanding of complex diseases, such as cancer, autoimmune disorders, psychiatric disorders and neurological diseases. Since MZ twins are genetic clones (genetically identical), they are considered as perfect models for studying the role of environmental factors as determinants of complex diseases and phenotypes. In this review, a number of intrauterine effects and genetic mechanisms that may affect phenotypic, genotypic, and epigenetic differences between MZ twins were described and effects of epigenetic mechanisms on complex diseases were mentioned. Further work on epigenetic changes in diseases using incompatible MZ twin models, would lead to new developments in medical therapies.