Substance dependence (SD) has a complex etiology, with constituents of risk that include genetic, neurobiological, and environmental factors. The D2 dopamine receptor gene (DRD2), the protein product of which links to the brain mesocortical dopamine reward system, has been the focus of much attention in addiction genetics, and in psychiatric genetics in general. There is a large volume of inconsistent research on the possible association of SD with the putative DRD2 TaqI “A” polymorphism, which has been shown to be located in ANKK1, an adjacent gene (Neville et al., 2004).
