Intellectual performance and school failure in children with attention deficit hyperactivity disorder and in their siblings.

We made psychiatric and intellectual assessments of 140 children with attention deficit hyperactivity disorder (ADHD), 120 normal controls, and their 303 siblings. The index children were white, non-Hispanic boys. ADHD children were more likely to have had learning disabilities, repeated grades, been placed in special classes, and received academic tutoring. They also did worse on the Wechsler Intelligence Scale for Children--Revised (WISC-R). Among ADHD probands, comorbid conduct, major depressive, and anxiety disorders predicted school placement more than school failure or WISC-R scores. However, the neuropsychological disability of all ADHD children could not be attributed to comorbid disorders because those without comorbidity had more school failure and lower WISC-R scores than normal controls. Intellectual impairment was also increased among siblings of ADHD children. This provides converging evidence that the ADHD syndrome is familial.