Polymorphism of ADH and ALDH genes among four ethnic groups in China and effects upon the risk for alcoholism.

The alcohol dehydrogenases (ADHs) and aldehyde dehydrogenases (ALDHs) that metabolize ethanol are polymorphic. Different alleles encode subunits of the enzymes that differ in their rate of metabolizing ethanol. These polymorphisms are distributed differently among populations and have been shown to influence the risk for alcoholism in some Asian populations. We have examined the allele frequencies at the ADH2, ADH3, and ALDH2 loci in four populations from China (Han, Mongolian, Korean, and Elunchun) and in alcoholics within each population. The four populations differ in allele frequencies, with the Elunchun having a much lower frequency of ADH2*2 alleles, and the Mongolian and Elunchun having a much lower frequency of ALDH2*2 alleles. Within each population, alleles at one or more of these three loci are protective against alcoholism, although the populations differ in which loci play significant roles. The protective allele at each locus (ALDH2*2, ADH2*2, and ADH3*1) encodes a subunit that either metabolizes ethanol to acetaldehyde more rapidly or slows the conversion of acetaldehyde to acetate. Taken as a whole, data demonstrate that genetic differences in the enzymes that metabolize alcohol can substantially affect the risk for alcoholism.