DRD4 and alcohol abuse: VNTR polymorphisms (variable number tandem repeat polymorphism) in DAT1/SLC6A3, a gene coding for a dopamine transporter protein (DAT), as well as functional polymorphisms in COMT (catechol-O-methyltransferase), DRD2 (dopamine D2 receptor) and DRD4 (dopamine D4 receptor) were analyzed in 94 non-treatment seeking patients with alcohol use disorder.