The present invention provides peptides that specifically bind to maternal autoantibodies that are generated in the mother or potential mother against one or more endogenous polypeptide antigens selected from lactate dehydrogenase A (LDH A), lactate dehydrogenase B (LDH B), stress-induced phosphoprotein 1 (STIP1), guanine deaminase (GDA), Y Box Binding Protein 1 (YBX1), collapsin response mediator protein 1 (CRMP1), and collapsin response mediator protein 2 (CRMP2). The peptides described herein are useful for determining a risk of an offspring for developing an autism spectrum disorder (ASD) by detecting the presence of maternal autoantibodies in a biological sample of the mother or potential mother. The peptides or mimotopes thereof can also be administered to the mother or potential mother to block the binding between maternal autoantibodies and their antigens, thereby neutralizing the maternal autoantibodies.