The combined search yielded 1024 references. After discarding the overlapping references and those which clearly did not meet the criteria, 91 studies remained. These studies were then filtered to ensure conformity with the inclusion criteria (13 studies(13–26) were excluded (Supplement 1)). In the end, 78 case-control studies (Table S1 in Supplement 1) met our criteria for inclusion. These studies included 48 studies (5, 14, 27–61) of Asian populations; 21 studies(43, 62–78) of European populations; four studies(79–82) of Mexican Americans; one(76) of African Americans; and four studies(76, 79, 83) investigating the Cys allele (Native Americans, African Americans, and Trinidadians). Among these studies, two(48, 68) investigated heroin dependence or abuse; three(76) investigated multi-drug dependence, and the other 73 studies investigated AD or AD and alcohol abuse. These 73 studies included 18 studies(28, 32, 35, 36, 44, 46, 50, 62, 63, 65, 66, 70–72, 74, 75, 77) in which the alcoholic patients were affected by alcoholic liver disease, cirrhosis, and (or) pancreatitis (10 of the 18 studies also included data for the patients without any alcohol-induced diseases). These studies included 9,638 cases and 9,517 controls. The results are detailed below.
