Alcohol use disorders are common illnesses that profoundly impact the lives of affected individuals, their families, and those with whom they interact (World Health Organization 2004; Hasin et al. 2007). The heritability of alcohol dependence has been estimated to be at least 50% by large twin studies (Heath et al. 1997; Prescott & Kendler, 1999; Tsuang et al. 2001; Knopik et al. 2004) with the remaining contribution to liability attributed to individual-specific environmental sources. Included among genes implicated in genetic studies are those whose products are involved in the metabolism [ADH clusters (Luo et al. 2005b; Edenberg et al. 2006; Luo et al. 2006; Macgregor et al. 2009)] and effects [GABRA2 (Covault et al. 2004; Edenberg et al. 2004; Lappalainen et al. 2005; Fehr et al. 2006), CHRM2 (Wang et al. 2004; Luo et al. 2005a)] of ethanol; however, replicated findings to date explain only a minority of the overall genetic risk.
