Differences between mentally retarded and normally intelligent autistic children.

Autistic children with an IQ below 70 and with an IQ above 70 were systematically compared. The two groups differed somewhat in the pattern of symptoms, but were closely similar in terms of the main phenomena specifically associated with autism. However, the low IQ and high IQ autistic children differed more substantially in terms of other symptoms such as self-injury and stereotypies and there were major differences in outcome. The possibility that the nature of the autistic disorder may differ according to the presence or absence of associated mental retardation needs to be taken into account in planning studies of etiology.