Autism (MIM 209850) is a severe, lifelong neurodevelopmental disorder characterized by impairments in communication and socialization, and by repetitive behavior. Recent studies of sub-microscopic genomic copy number variation (CNV) have identified several loci associated with Autism Spectrum Disorder (ASD; MIM 209850) (1,2). De novo CNVs associated with ASD have been reported in ~7% of simplex families and ~2% of multiplex families (2,3). CNV studies have also led to the identification of autism candidate genes such as SHANK3 (MIM 606230) and NRXN1 (MIM 600565) (1,4,5). Intellectual disability (ID) is frequently associated with autism (in up to ~30% of cases for ASD, and ~67% for autism) (6). Moreover, mutations in several X-linked ID (XLID) genes (e.g. NLGN4 and IL1RAPL1) have been shown to result in an autistic phenotype, which suggests that autism and ID may often share a common genetic etiology (3,7-10). We previously reported a 167 Kb microdeletion of exon 1 of PTCHD1 (NM_ 173495.2) on chromosome Xp22.11 (3). PTCHD1 has three exons spanning ~62 Kb and it is predicted to encode a protein of 888 amino acids. In silico analysis
