As one of the core features of ASDs, restricted repetitive behavior (RRB) frequently dominates the daily activities of affected children, interferes with opportunities to develop functional behaviors, and requires intervention and treatment. The objective of this study is to identify contributing genetic factors for abnormal repetitive behavior (such as flapping arms, lining up objects, peculiar fascination with odd objects, a very narrow restricted interest, and intolerance to changes of routines) among children with autism spectrum disorders (ASDs). Researchers will investigate whether genetic variations within the GABA and glutamate neurotransmission system play a role in the pathogenesis of RRB in children with ASDs. Using behavioral rating scales, medical histories, and parental input, researchers will measure the extent of RRBs in children with ASD (ages 6-18). Biomaterials from these children, like saliva and buccal swabs, will be used to genotype GABA and glutamate system-related genes, allowing researchers to correlate genetic variants with RRB behavioral measures. Positive findings may lead to a new insight as to early detection and treatment of this chronic and disabling condition.