Replication was sought in an independent dataset of 825 Icelandic patients with ADHD (238 female and 587 male participants) from deCODE Genetics. All participants met DSM-IV criteria for ADHD (477 combined type, 250 inattentive type, 58 hyperactive-impulsive type, 40 unspecified), and those with schizophrenia and autism were excluded from the sample. Participants were recruited from outpatient paediatric, child, and adult psychiatry clinics in Iceland, and diagnoses had been made on the basis of standardised diagnostic assessments and had been reviewed by experienced clinicians.20,21 These participants were compared with 35 243 Icelandic controls, also from deCODE Genetics. CNV analysis in this sample has been previously described.22
