Exome Sequencing in Autistic Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by functional deficits in three domains: social interaction, communication, and stereotypic behavior. Prevalence has been estimated to be approximately 1/166 children and the public health impact is significant. ASD clearly has a genetic component; however, identification of specific etiologies has been complicated by the heterogeneous nature of ASD. One approach to minimize this problem is to define endophenotypes that can subcategorize ASD patients. Based on our work with Smith-Lemli-Opitz syndrome, we have investigated whether alterations in cholesterol homeostasis may contribute to ASD. We found in 200 ASD subjects that 23% of subjects had serum cholesterol levels less than or equal to 2.28th centile and 9% had levels greater than or equal to 97.72nd centile. Analysis of the sterol profile suggested that the hypocholesterolemia was due to a synthetic defect rather than decreased oral intake. Thus we hypothesize that ASD patients with abnormal cholesterol levels will have polymorphisms or mutations of either genes involved in cholesterol homeostasis or genes encoding proteins whose function is altered by changes in cholesterol levels. To test this hypothesis we propose to 1) use serum cholesterol levels to define ASD endophenotypes and 2) to perform genomic resequencing of all known exons in hypo- and normocholesterolemic ASD patients.