While environmental factors likely play an important role in the development and evolution of autism, their specific mechanism and, most importantly, their gene targets are unknown. We intend to study mechanisms by which the environment influences autism by studies in the exciting new field of epigenetics that links genes, environment, and disease. Epigenetics is a form of hereditary information that does not involve DNA sequence (i.e., the genetic code), but it influences whether a gene is turned on (i.e., whether the code is read). A major component of epigenetics is DNA methylation, a chemical change in DNA that is reproduced during cell division and is associated with gene silencing. DNA methylation is affected by a variety of environmental factors including diet. We hypothesize that epigenetic abnormalities contribute to the etiology of autism, and that by studying these abnormalities we could better understand autism's clinical variability as well as identify genes that may undergo epigenetic change in some patients, and conventional mutations in the genetic code in others. A compelling argument in support of our hypothesis is that monozygotic (genetically identical) twins are often discordant for autism, i.e., there is marked disparity in the degree of autism, suggesting the importance of factors other than the DNA sequence, like DNA methylation. We will test this idea by studying DNA methylation in such monozygotic twins who are discordant for autism. As demonstrated in our preliminary findings, we have already discovered genes that are abnormally methylated in the more affected twin. We will then examine whether the identified epigenetic changes are relevant to most patients with autism, by determining whether the same genes show altered DNA in autistic subjects in the general population, compared to control individuals. We will also determine whether patients not showing altered DNA methylation in these genes have conventional DNA sequence changes in the same genes, potentially linking genetic and epigenetic alterations in autism. This project will combine novel and sensitive high-throughput epigenomics strategies developed by the Initiating Principal Investigator (PI), a pioneer in epigenetics, with detailed phenotypic analyses by the Partnering PI, a leader in the study of autism in genetic disorders. These studies should have immediate practical implications for autism diagnosis. In addition, this work raises the exciting possibility of discovering mechanisms for autism that might be treatable, since epigenetic changes are potentially reversible, unlike DNA sequence mutations.