For example, variability in the gene(s) encoding the dopamine D2 receptor (DRD2) and/or its adjacent ankyrin repeat and protein kinase domain-containing protein 1 (ANKK1) has been implicated in dependence to nicotine, heroin and cocaine, as well as alcoholism and abuse of psychostimulants (7, 10). In addition, genes that influence dependence in a drug-specific manner have also been implicated. For example, variability in cytochrome P450 2A6 (CYP2A6), the main enzyme involved in the metabolism of nicotine, has been associated with smoking behaviors (4). Table 2 summarizes the different candidate genes implicated in drug addiction and the literature where they have been reviewed in greater detail.
