Epigenetics lessons from twins: prospects for autoimmune disease.

The existence of phenotypic differences between monozygotic (MZ) twins is a prime case where the relationship between genetic determinants and environmental factors is illustrated. Although virtually identical from a genetic point of view, MZ twins show a variable degree of discordance with respect to different features including susceptibility to disease. Discordance has frequently been interpreted in terms of the impact of the environment with genetics. In this sense, accumulated evidence supports the notion that environmental factors can have a long-term effect on epigenetic profiles and influence the susceptibility to disease. In relation with autoimmune diseases, the identification of DNA methylation changes in individuals who develop the disease, and the influence of inhibitors of DNA methyltransferases and histone modification enzymes in the development of autoimmunity are attracting the attention of researchers in the epigenetics field. In this context, the study of discordant MZ twins constitutes an attractive model to further investigate the epigenetic mechanisms involved in their development as well as to dissect the contribution of environmental traits. The implications of novel strategies to map epigenetic profiles and how the use of MZ twins can contribute to dissect the epigenetic component of autoimmune disease are discussed.