DRD4 and attention deficit-hyperactivity disorder: In an earlier investigation on the Indo-Caucasoid ADHD probands, we have noticed additive effects of DBH rs1108580 and DRD4 rs1800955, while the DRD4 exon 3 VNTR, DAT1 3′UTR and intron 8 VNTR, MAOA u-VNTR, rs6323, COMT rs4680, rs362204, DBH rs1611115, and rs1108580 were found to exert strong independent effects [5].