Despite these limitations, significant progress has been made, especially for AD and ND. Linkage studies have identified a locus on chromosome 4q near the ADH gene cluster as a major locus for alcoholism in American Indians and Caucasians,13–15 in addition to the known ADH2 and aldehyde dehydrogenase 2 (ALDH2) variants in Asians and Jewish Americans.16–18 The ADH locus contains a cluster of seven genes, of which ADH2 is the most important across populations,19 although functional variants in ADH4 and ADH7 might also be involved.16,20,21
