Genetics of autism

We have learned more about the molecular genetics of autism in the last 3 years than in the previous 30. This includes both a new appreciation for the role of rare genetic variation and the identification of the first contributory common variants by genome-wide association. These data show that although the population attributable risk of common variation may be moderate to large, the genotype risk of common variants at the individual level are small. In contrast, a large number of diverse rare mutations of large effect have been identified, but none appear specific to autism. All of these findings point to extreme genetic heterogeneity suggesting complex gene-gene or gene-environment interactions in autism etiology. Available knowledge, reviewed below, also suggests that phenotypic presentation is the result of complex interactions, and that implicated genetic risk factors in many cases cross the boundaries of established clinical diagnostic categories. Acceptance of this complexity and efforts to understand genetic variation in terms of intermediate phenotypes represent important directions for future research.