The risk for
drug addiction is partially heritable. Genes of the
dopamine system are likely candidates to harbour risk variants, as
dopamine neurotransmission is involved in mediating the rewarding effects of drugs of abuse. One functional single nucleotide polymorphism in
dopamine receptor D2 (DRD2), rs1076560, is involved in regulating splicing of the gene and alters the ratio of DRD2
isoforms located pre- and postsynaptically. rs1076560 has been previously associated with
cocaine abuse and we set out to confirm this association in a sample of European American (EA) (n = 336) and African American (AA) (n = 1034)
cocaine addicts and EA (n = 656) and AA (n = 668) controls. We also analysed the role of rs1076560 in
opioid dependence by genotyping EA (n = 1041) and AA (n = 284)
opioid addicts. rs1076560 was found to be nominally associated with
opioid dependence in EAs (p = 0.02, OR = 1.27) and AAs (p = 0.03, OR = 1.43). When both
opioid-addicted ancestral samples were combined, rs1076560 was significantly associated with increased risk for
drug dependence (p = 0.0038, OR = 1.29). This association remained significant after correction for multiple testing. No association was found with
cocaine dependence. These data demonstrate the importance of
dopamine gene variants in the risk for
opioid dependence and highlight a functional polymorphism that warrants further study.