Since CNVs occur with increased frequency in patients with unexplained intellectual disability,17 we needed to exclude the possibility that any increased rate of CNVs recorded for these disorders was not a result of comorbidity with intellectual disability. Therefore, assessments of intellectual ability were undertaken for the ADHD group. Intellectual disability was assessed with the Wechsler Intelligence Scale for Children-IV,18 and complete test scores were available for 396 children. In accordance with DSM-IV and ICD-10, individuals with IQ test scores lower than 70 were regarded as having intellectual disability.
