et al., 2004; Bond, et al., 1998; Comings, Blake, et al., 1999; Crowley, et al., 2003; Franke, et al., 1999; Li, et al., 2000; Mayer, et al., 1997; Shi, et al., 2002; Szeto, Tang, Lee, & Stadlin, 2001; Tan, Tan, Karupathivan, & Yap, 2003; K. Xu, Liu, Nagarajan, Gu, & Goldman, 2002; Yuferov, et al., 2004; Zimprich, et al., 2000), GABAergic system genes for alcohol dependence (Noble, et al., 1998), and nicotinic cholinergic system genes for nicotine dependence (Saccone, et al., 2007). Additionally, because of the central role that dopaminergic systems are thought to play in drug reward, reinforcement, addiction and dependence, dopaminergic system genes have been investigated in relation to addiction to substances that do not directly affect dopamine, including ethanol (Blum, et al., 1993; Gelernter & Kranzler, 1999; Gorwood, et al., 2003; Noble, 1998a, 1998b; Noble, et al., 1998; Sander, Harms, Podschus, et al., 1997), and opiates (Kotler, et al., 1997; Lawford, et al., 2000). Opioid systems have also been investigated in regard to dependence on drugs other than opiates (Bergen, et al., 1997; A. C. H. Chen, et al., 2002; Dahl, et al., 2005; Franke, et al., 1999; Ide, Kobayashi, et al., 2004; Xuei, et al., 2006).
