Research has focused on identifying subgroups of people with autism, or "endophenotypes," in order to accelerate the discovery of autism's genetic basis. People with the same endophenotype share certain traits, which may include morphological, physiological or behavioral features. This research project explores a candidate endophenotype based on motor ability. Dr. Constantino's fellow will evaluate the coordination of movement in school-aged children with autism and their siblings. The subjects will come from a well-characterized sample of sibling pairs that either share autism (concordant) or do not share autism (discordant), and this sample includes both Caucasian and African-American families. By analyzing how motor abilities vary among autistic and non-autistic siblings, this work will test the reliability of this candidate endophenotype. In addition, the early development of motor abilities will be studied in a different sample of high-risk infant siblings of individuals with autism.