Autism spectrum disorders (ASD) is a common childhood-onset, multi-factorial, highly heritable, clinically and genetically heterogeneous, neurodevelopmental disorder. Due to its high prevalence and severe lifelong impairment without effective prevention and treatment, there is a dearth of investigating its pathogenesis, longitudinal outcome, and biomarkers (endophenotypes). The ultimate goals of this 5-year project are to prospectively investigate the outcome and changes of psychosocial and neurocognitive functions of a cohort of probands with ASD at adolescence and young adulthood as the primary aim; and to test whether structural and functional brain connectivity can be effective endophenotypes of ASD using the unaffected sibling and follow-up designs as the secondary aims.