t is well established that the risk of developing autistic behavior in greatly increased in Fragile X Syndrome, which occurs solely in males. While they have similar mutations in a gene called FMR1, symptom severity divides the affected males into three groups: those with mild, moderate and severe autism symptoms. The investigators, who are senior genetic psychiatric researchers, will use Fragile X Syndrome as a "toehold" into autism, conducting a pilot study that will provide the basis for applying to other funders for a larger-scale genetic study. They hypothesize that they can identify genes that predispose males with Fragile X Syndrome to autistic behavior. Aims of the pilot study are to: 1) Develop a sample of 150 males with Fragile X Syndrome; 2) Assess the degree of their autistic behavior; 3) Obtain DNA samples and establish the mutation status of the FMR1 gene; 4) Examine 768 genetic markers in 25 genes that they suspect are strong candidates for autism behaviors: and 5) Find statistical associations between the 25 genes' make-up and the degree of autism symptoms. If successful, they will have identified genes that predispose to autistic behavior in males with Fragile X Syndrome, setting the stage for a large-scale study of these genes in people with autism. Significance: The study of a small field of genes that are associated with autistic behaviors in males with this related disease could further pinpoint candidate genes that then could be efficiently studied in people with autism. Ultimately, this work could advance understanding of the genetic aspects of autism.