While Dr. Gilmore and colleagues at the University of North Carolina will be studying the relationship between early testosterone levels and later brain development using structural imaging techniques, Dr. Livesey at the University of Cambridge will be investigating the influence of testosterone on early brain development in an animal model. T his project will determine if testosterone can control the levels of FGF8, a protein which is necessary for the normal development of the brain. The animal study will be conducted alongside a clinical experiment which will test blood levels of FGF8 and a set of genes that FGF8 controls in a population of children with diagnosed with autism and those not affected. By combining experimental studies using mouse as a model system with a pilot study to investigate possible cellular mechanisms of altered brain development in individuals with autism spectrum disorders, this research will generate fundamental data on this promising theory for the cause and pathogenesis of autism. Significance: While the cause of autism spectrum disorders is unknown, disruption in the fetal exposure to testosterone levels is hypothesized to contribute to some of the behavioral symptoms. However, the question arises as to how increased androgens could lead to the varied neurological signs and symptoms associated with autism. Therefore, this study will investigate the possible biological mechanisms by which high levels of fetal androgens could affect forebrain development and lead to the development of autistic spectrum conditions.