Clinical and cognitive characteristics of children with attention-deficit hyperactivity disorder, with and without copy number variants

BACKGROUND Submicroscopic, rare chromosomal copy number variants (CNVs) contribute to neurodevelopmental disorders but it is not known whether they define atypical clinical cases. AIMS To identify whether large, rare CNVs in attention-deficit hyperactivity disorder (ADHD) are confined to a distinct clinical subgroup. METHOD A total of 567 children with ADHD aged 5-17 years were recruited from community clinics. Psychopathology was assessed using the Child and Adolescent Psychiatric Assessment. Large, rare CNVs (>500 kb, <1% frequency) were defined from single nucleotide polymorphism data. RESULTS Copy number variant carriers (13.6%) showed no differences from non-carriers in ADHD symptom severity, symptom type, comorbidity, developmental features, family history or pre-/perinatal markers. The only significant difference was a higher rate of intellectual disability (24% v. 9%, χ(2) = 15.5, P = 0.001). Most CNV carriers did not have intellectual disability. CONCLUSIONS Large, rare CNVs are not restricted to an atypical form of ADHD but may be more highly enriched in children with cognitive problems.