The combined search yielded 820 references. After discarding overlapping references and those which clearly did not meet the inclusion criteria, 58 studies remained. These studies were then filtered to ensure conformity with the inclusion criteria. One study(Wei et al. 1999) was excluded because the cases and controls were related; one study(Poupon et al. 1992) because the controls were moderate alcohol drinkers; one study(Macgregor et al. 2009) because it was investigating twin pairs; one study(Khan et al. 2010) because the definition for “alcoholics” was not consistent with our inclusion criteria; and one study(Shafe et al. 2009) because no genotype data were available. In the end, 53 case-control studies (supplementary Table 1) met our criteria for inclusion. These studies included 30 studies(Chai et al. 2005; Chao et al. 1994; Chao et al. 2000; Chao et al. 1997; Chen et al. 1999; Chen et al. 1996; Chen et al. 1997; Choi et al. 2005; Fan et al. 1998; Higuchi et al. 1996; Kim et al. 2004; Lee et al. 2001; Lee et al. 1999; Montane-Jaime et al. 2006; Nakamura et al. 1996; Osier
