Autism and genetic disorders.

The syndrome of autism has been documented as occurring in association with a wide variety of genetic conditions. Autistic patients with a coexistent genetic condition, however, are not behaviorally or developmentally distinct from autistic patients for whom there is no known etiology or associated organic condition. This report reviews the literature linking autistic behavior with genetic conditions. Genetic, neurodevelopmental, and neuropathological findings in three genetic conditions which frequently give rise to autism are presented in detail. On the basis of this review, two hypotheses are supported: autism is a behaviorally defined phenotype which arises from diverse causes of central nervous system (CNS) damage, and the autistic phenotype represents only one point along a continuum of psychological dysfunction resulting from CNS damage. Current theories of genetic influences on brain development are reviewed, with emphasis on the relationships among qualitative, quantitative, and temporal abnormalities of CNS maturation and behavioral dysfunction. A hypothesis of abnormal brain development resulting from dysfunctional myelination is proposed as a potential etiologic factor in autism.