Because ADH1B and ADH1C are adjacent on chromosome 4, two main possibilities exist for their effects on alcohol phenotypes: (1) each influences the risk for alcohol phenotypes or (2) the associations found with one gene are due to “real” associations with the other. There is considerable linkage disequilibrium (LD) across the set of ADH genes in individuals of European decent (Luo et al., 2006; Edenberg, 2007). Further, different combinations of ADH1B and ADH1C (based on different genotypes) lead to interindividual differences in ethanol oxidation (Hurley et al., 1990). Therefore, both risk variants should be analyzed jointly to further understand how these SNPs influence alcohol phenotypes.
