Autism spectrum disorders (ASD) are a group of neurodevelopmental diseases. The cause of ASD is unknown, but several genetic and non-genetic risk factors have been characterized that, alone or in combination, are implicated in the development of ASD. Currently, no diagnostic biomarkers are available, and the diagnosis of ASD is based on typical features that include repetitive behaviors, and impaired social communication and interaction. Several pathomechanisms such as alterations in brain development and function, and synaptic defects have been proposed to contribute to these behaviors. In addition, processes outside the central nervous system may contribute to, or modify, the clinical phenotype and severity. This chapter summarizes the clinical features of ASD, highlights the important genetic and non-genetic risk factors for ASD, and introduces the current knowledge around the pathological processes within and outside the brain.
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