Previous research has shown that autism spectrum disorder is caused by a combination of both genetic and environmental factors. Although studies have identified genes that associated with having ASD, the specific pathways involved in the development and progression of ASD is not well understood. In addition, less is known about the genetic contributions to autistic traits in the more general population and also on the progression of these autistic traits. In this project we would like to address this important gap in our knowledge by investigating these genetic contributions in more detail and by attempting to identify the specific biological pathways that lead to the development of ASD, autistic traits and the progression of these traits over time. To do this we will use data from several cohorts, including Children of the Nineties. The results from this study may inform population health and may help develop more targeted interventions for individuals with ASD symptoms.