SNP data for our 100 most strongly associated SNPs were requested from deCODE Genetics and the ADHD GWAS Consortium. The deCODE sample included 1,142 Icelandic individuals who met DSM-IV criteria for ADHD. Patients were recruited from outpatient psychiatric clinics in Iceland. Diagnoses were based on standardized diagnostic assessments and were reviewed by experienced clinicians as previously described (22). A total of 35,243 Icelandic individuals were available as comparison subjects (22). The second sample consisted of 2,064 parent-child trios, 896 case subjects, and 2,455 comparison subjects from the ADHD GWAS Consortium meta-analysis and has been described in detail elsewhere (10). This data set consists of four projects: the Children's Hospital of Philadelphia, phase I and phase II of the International Multisite ADHD Genetics Project, and a Pfizer-funded study from the University of California, Los Angeles, Washington University, and Massachusetts General Hospital.
