Several findings have suggested DRD2 as a potential candidate gene that might contribute to the genetic susceptibility to various types of dependence. For example, the dopamine system in general is involved in dependence on a variety of drugs (Smith et al. 1992). Moreover, numerous association studies have specifically implicated the DRD2 gene in the development of alcohol dependence (see Edenberg et al. 1998) as well as in smoking (Spitz et al. 1998). These findings, particularly regarding the association of DRD2 with alcohol dependence, are controversial, however. Many other studies found no associations between DRD2 polymorphisms and alcohol dependence, and linkage studies of DRD2 and alcohol dependence also yielded negative results (see Edenberg et al. 1998).
