Deficits in social behaviour and social communication, two core symptoms that define autism spectrum disorders, can also be observed in unaffected people but in a milder form. This suggests that autism relates to an underlying dimension. Furthermore, it has been shown that some severe deficits in individuals with autism and milder impairments in neurotypical individuals (autistic-like traits) relate to the same genetic variations. This project focuses on the identification of such quantitative genetic causes for autism in neurotypical children, specifically their variation in social communication skills and social behaviour. The advantage of the investigators' approach is that they can investigate large samples, which have access to a variety of measures for autistic-like traits but also potential environmental risk factors of autism. This approach provides an opportunity to study the joint effects of genetic and environmental risk-factors, and more importantly their interaction, as this will provide insight into how the effects of genetic risk variants can be changed and alleviated. Exploiting the recent advances in population genetics, they will perform this search genome-wide for both autistic-trait-related genetic variation, and interaction effects with potential environmental risk factors. The study, however, will not only examine genetic variation in children but also genetic variation in their mothers, which may exert additional effects on the embryonic environment for the developing child. Furthermore, it focuses on interactions with environmental factors, which can be changed through interventions. This will include risk factors before and during pregnancy such as maternal substance use and infections. The study also examines whether observed genetic and interaction signals can be confirmed in independent samples such as children from the general population with similar traits. The final aim is to integrate the findings into a model that follows social communication skills and social behaviour over time as these traits may vary during development. Investigation of genetic risk factors for autistic-like traits and their interactions with environmental exposures has strong implications for the identification of means to improve the lives of people with autism.