Several lines of evidence support a major genetic contribution to autism, including large visible chromosomal rearrangements detected in 3-7% of autism patients. However, little is known about the role of smaller, submicroscopic chromosomal abnormalities that are not readily detectable using traditional methods. Using a novel, state-of-the-art approach called array comparative genomic hybridization (aCGH), researchers have recently discovered a small deletion containing 24 genes on Chromosome 16p11.2 that represents one of the most frequent chromosomal abnormalities described in autism to date. In the proposed study, Dr. Kumar will extend this finding by selecting the most promising candidate genes for involvement in autism from this newly identified 16p11.2 chromosomal region. These genes will be examined in patients to search for the presence of mutations significantly associated with autism. As well, aCGH will be used to identify additional novel submicroscopic chromosomal rearrangements in a sample of approximately 300 autism patients who have not been previously tested for these abnormalities. The identification of novel candidate genes and chromosomal abnormalities in autism patients will further our understanding of the genetic factors conferring risk of autism, and may improve the accuracy of diagnostic tests for this disorder.