Direct associations were identified between the dopamine receptor 3 (DRD3) BalI polymorphism and depression; the dopamine receptor 1 (DRD1) and dopamine transporter gene 3' VNTR polymorphisms and aberrant motor behavior; the DRD4 VNTR and sleep disturbances; and the SERT gene VNTR 5HTTLPR and apathy items.
There was a trend for DRD4 long alleles of the variable number of tandem repeats polymorphism to be associated with reduced severity of three withdrawal symptoms [desire/craving (P = 0.054); anger/irritability (P = 0.10); and trouble sleeping (P = 0.068)].