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.