Autism spectrum disorders are among the most common heritable disorders known, though for reasons unknown, four times as many males as females are affected with autism. To investigate genetic causes for this sexual dimorphism, we are using genome-wide genetic data to make comparisons between males and females in order to distinguish various genetic models and to identify sex-specific genetic susceptibility loci. If we can determine what protects females from developing autism, that information could lead not only to biological insights, but potentially to reduction of male risk.