Genetic variation on chromosome 15 (e.g., 15q11-q13) is common and can cause numerous brain disorders, including Prader-Willi syndrome, Angelman syndrome, mental retardation, autism, epilepsy, schizophrenia, and bipolar disorder. Researchers in this study will better define genotype/phenotype correlations stemming from mutations and gene alterations in this region of chromosome 15. They will utilize gene expression analysis and epigenetic studies of human brain tissue comparing duplications of the 15q11-q13 region with controls. Duplications of this region on the maternal chromosome specifically cause autism, while duplications on the paternal chromosome do not. Therefore, understanding the molecular basis for this difference should shed considerable light on the causes of autism that are not caused by changes in DNA sequence.