The prevalence of autistic disorder among children with a learning disability.

It has been suggested recently that the prevalence of autistic disorder may be rising. No prevalence study specifically among learning disabled children exists and so this study was prompted. 767 children with a learning disability who attended 16 different special schools in the Grampian region of north-east Scotland were studied for a diagnosis of autistic disorder according to the DSM-III-R criteria. The study was conducted in three stages. In the first screening stage, a questionnaire was completed for each child by their teachers. In the second stage, teachers completed another questionnaire based on DSM-III-R criteria for autistic disorder. A final diagnosis was made on the basis of examination and information gathered from the questionnaires. Questionnaires were completed for 634 (82.7%) children. 14.3% of children with a learning disability fulfilled the diagnostic criteria for autistic disorder. There was a male:female ratio of 3:1. This gave a 9 per 10,000 minimum prevalence of autistic disorder among all school-age children in the Grampian region. There was a higher prevalence of autistic disorder in the cities compared with rural areas. The prevalence did not change with age but increased with decreasing IQ. The results of the study support the view that there may be an increasing prevalence of reported cases of autistic disorder.