Complex Neurodevelopmental Disorders

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Autism and autism spectrum disorders are complex neurodevelopmental disorders. Many causes of autism have been proposed, but its theory of causation is still incomplete.[1] Heritability contributes about 90% of the risk of a child developing autism, but the genetics of autism are complex and typically it is unclear which genes are responsible.[2] In rare cases, autism is strongly associated with agents that cause birth defects.[3] Many other causes have been proposed, such as exposure of children to vaccines; these proposals are controversial and the vaccine hypotheses have no convincing scientific evidence.[4] Autism is a condition involving abnormalities of brain development and behavior which manifests itself before a child is three years old and has a steady course with no remission. It is characterized by impairments in social interaction and communication, as well as restricted and repetitive behavior. It is part of a larger family called the autism spectrum disorders (ASD) or pervasive developmental disorders (PDD), which include closely related syndromes such as Asperger syndrome and PDD-NOS.[5][6] This article uses autism to denote the classic autistic disorder and ASD to denote the wider family. Autism's theory of causation is still incomplete.[1] There is increasing suspicion among researchers that autism does not have a single cause, but is instead a complex disorder with a triad of core aspects (social impairment, communication difficulties, and repetitive behaviors) that have distinct causes but often co-occur.[7] The number of people known to have autism has increased dramatically since the 1980s, at least partly due to changes in diagnostic practice; it is unknown whether prevalence has increased as well.[8] An increase in prevalence would suggest directing more attention and funding toward changing environmental factors instead of continuing to focus on genetics. The diagnosis of epilepsy requires that the seizures be unprovoked, with the...
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