Family, twin and adoption studies show that genes play a substantial role in the etiology of attention-deficit hyperactivity disorder (ADHD) 1 but the genetic architecture of the disorder is unknown. Meta-analysis of seven ADHD linkage scans identified several genomic regions with suggestive evidence of linkage but only one region (16q22–q24) was statistically significant genome-wide. 2 An important and widely applied tool in psychiatric genetics is the genome-wide association study (GWAS).
