Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by impairments in communication (verbal and nonverbal), social interactions, and stereotyped behaviors/interests. The etiology of ASD is not well understood, though it likely involves both genetic and environmental factors. Immune system dysfunction has been reported in ASD in many studies. Systemic immunologic alterations in autistic individuals often have been associated with autoimmunity; in particular, the generation of antibodies reactive against brain and central nervous system proteins. For example, both abnormalities in serum antibody concentrations and T cells have been reported for ASD compared to typically developing children. The goal of this grant proposal is to identify serum antibody biomarkers for ASD using a novel combinatorial peptoid library that has been successful for the identification of antibody biomarkers for Alzheimer's disease. An ASD blood biomarker would be very useful for early identification and targeted therapeutic intervention.