This grant provides support for an NIH Autism Center of Excellence (ACE). This study seeks to identify early manifestations of abnormal brain development in autism spectrum disorders (ASD). Twelve-month old infant siblings of children with autism, and comparison non-risk infants, will be studied using magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI), and relationships between brain measures and clinical course and symptom onset will be examined. A second part of the research will examine children entering adolescence in order to identify brain developmental changes that may be related to onset seizure and behavioral decline during the adolescent period. This study will enable understanding of the relationship between variations in brain development and longer-term clinical outcome, focusing on adolescent seizure onset and cognitive decline.