The validity of autistic spectrum disorders: a literature review.

The objective of this literature review is to assess the validity of autistic spectrum disorders (ASD). Twenty papers were identified that adequately investigated the internal or external validity of various subtypes of ASD. At least three groups can be distinguished from autism on clinical grounds; an Asperger syndrome subtype, and two atypical subtypes characterized by low IQ and high IQ. However, the evidence that these clinical distinctions carry inferences with respect to etiology, clinical course, and treatment is only suggestive. Nevertheless, the specification of several ASD subtypes might promote further research and resolve many of the nosologic issues with respect to the classification of pervasive developmental disorders (PDDs).