Although clinically and genetically variable, there are several emerging themes as to the underlying causes of autism spectrum disorders (ASD). Post-mortem and magnetic resonance imaging (MRI) studies have identified a number of brain structures that are anatomically abnormal in autistic individuals, including the cerebellum. Dr. Millen's research group has identified a number of genes and chromosomal loci that cause abnormal development of the cerebellum. In this study, they will attempt to establish a link between ASD and genetically defined human cerebellar malformations, testing the hypothesis that genes causing these malformations also represent an important subset of genes that confer susceptibility to ASD. Using genetic information from individuals with ASDs, including large publicly available genetic datasets, they will search for variation in known human cerebellar malformation genes to determine whether mutations in these genes are associated with ASD. They will also examine whether people harboring known ASD-related genetic changes have cerebellar abnormalities that are visible by MRI brain imaging.