ASDs show a large genetic component, with estimates of heritability as high as 60- 90%. However, the extreme heterogeneity of ASD is a persistent hurdle to gene discovery, and known genetic causes account for less than 15% of diagnoses. This study will analyse the DNA of consanguineous families (those where the parents share ancestry) diagnosed with ASD to locate regions of the genome likely to harbor the mutation that causes their ASD, and perform whole genome sequencing (WGS) on the affected individuals to identify candidate variants. High throughput methods of functionally validating strong candidate genes discovered through WGS using yeast models, transformed somatic cell lines, and other model systems will also be developed. Finally, to examine the effects of removing the genes discovered in this study on dendrite and dendritic spine morphology and synaptic activity, mouse models of candidate genes will be developed.