Autism spectrum disorder (ASD) is a complex pervasive neurodevelopmental disorder with an estimated lifetime prevalence of 1%. ASD presents across a wide range of intellectual ability and persists throughout life. Core symptoms include abnormal social interaction and communication, restricted and repetitive interests or activities, associated with lack of cognitive flexibility, and unusual sensory responses. ASD is highly heritable and polygenic. The male:female ratio of ASD is 3:1. Although the behavioural presentation has a childhood onset, approximately 40% of children with ASD are undiagnosed.