Interaction between the functional polymorphisms of the alcohol-metabolismgenes in protection against alcoholism

The genes that encode the major enzymes of alcohol metabolism, alcohol dehy drogenase (ADH) and aldehyde dehydrogenase (ALDH), exhibit functional polym orphism. The variant alleles ADH2*2 and ADH3*1, which encode high-activity ADH isoforms, and the ALDH2*2 allele, which encodes the low-activity form o f ALDH2, protect against alcoholism in East Asians. To investigate possible interactions among these protective genes, we genotyped 340 alcoholic and 545 control Han Chinese living in Taiwan at the ADH2, ADH3, and ALDH2 loci. After the influence of ALDH2*2 was controlled for, multiple logistic regre ssion analysis indicated that allelic variation at ADH3 exerts no significa nt effect on the risk of alcoholism. This can be accounted for by linkage d isequlibrium between ADH3*1 and ADH2*2 ALDH2*2 homozygosity, regardless of the ADH2 genotypes, was fully protective against alcoholism; no individual showing such homozygosity was found among the alcoholics. Logistic regressi on analyses of the remaining six combinatorial genotypes of the polymorphic ADH2 and ALDH2 loci indicated that individuals carrying one or two copies of ADH2*2 and a single copy of ALDH2*2 had the lowest risk (ORs 0.04-0.05) for alcoholism, as compared with the ADH2*1/*1 and ALDH2*1/*1 genotype. The disease risk associated with the ADH2*2/*2-ALDH2*1/*1 genotype appeared to be about half of that associated with the ADH2*2/*2-ALDH2*1/*1 genotype. T he results suggest that protection afforded by the ADH2*2 allele may be ind ependent of that afforded by ALDH2*2.