Research has indicated that the 10R of the 40 bp VNTR in the 3′ untranslated region (3′UTR) of DAT1 is strongly correlated with clinical symptoms in ADHD children, particularly those with attention deficits and that DAT1 haplotypes comprising the 10R of the 40 bp VNTR of the 3′UTR/the 6R of the 30 bp VNTR of the intron 8 are strongly correlated with cognitive impairments in ADHD. This evidence concerns the gene SLC6A3 and attention deficit-hyperactivity disorder.