An MRI study of the corpus callosum and cerebellum in mentally retarded autistic individuals.

The areas of seven subregions of the corpus callosum and three subregions of the cerebellum were examined on midsagittal magnetic resonance imaging scans of 27 low-IQ autistic individuals and 17 nonautistic individuals of comparable mental age. Autistic individuals had a significantly smaller corpus callosum (most marked in the body). No significant between-group differences were found in cerebellum areas. Results demonstrate that abnormalities of the corpus callosum reported in high-functioning autistic individuals are also present in autistic individuals with mental retardation and extend previous reports showing no evidence for a selective hypoplasia of cerebellar lobules VI-VII.