This project will investigate the genetic underpinnings of language development by studying language-related abilities in families of children with autism. Autism is a severe developmental disorder defined by profound impairments in language, as well as social-emotional functioning and restricted, repetitive interests and behaviors. Although evidence supports a role of genetic factors in autism, the identification of susceptibility genes remains an elusive goal. This project will characterize developmental language profiles present among unaffected family members (parents and siblings), which may be linked to the genes involved in autism. To do so, this study capitalizes on an unprecedented opportunity -- the availability of archival childhood language testing records from a large cohort of families with a child with autism. Using these valuable data, the study will characterize language development of parents and siblings longitudinally over the early school-age years, documenting these relatives' developmental pathways of early language functioning that may be related to the genes involved in autism. The study will also collect DNA from individuals with autism and their family members so that their profiles may be applied to genetic studies examining links to specific genetic variants. Finally, this research will examine relatives' current language profiles and address environmental factors that may protect or augment baseline genetic liability. This could reflect gene-environment interactions, which are critical in understanding factors that influence language development. Autism is a major public health concern. Though once considered to be relatively rare, striking new prevalence estimates of 1 in 150 recently prompted the Centers for Disease Control and Prevention to declare autism a national public health crisis. Such reports underscore the pressing urgency for determining the cause of this serious disorder. Information obtained from this study will help target genetic research in autism via the study of genes differentially associated with language functioning in families with a child with autism. That is, by examining developmental pathways of early language functioning among relatives, the study aims to identify developmental profiles that may reflect genetic liability to autism and will be used in current and future molecular genetic studies. In addition, results provide insight into the underpinnings of language development more generally. The study of developmental growth in genetically-based disorders such as autism can provide crucial insights into genetic and environmental processes of healthy development. Findings from this research may therefore provide a foundation for future work on the genetics of language.