and ADH variants that increase function (and the production of acetaldehyde) may also be protective (see, e.g., Thomasson et al. 1991; Hasin et al. 2002; Konishi et al. 2003). Work with ALDH2 provides an instructive and intuitive example of this work, as a variant common in Asians abolishes function of this gene and therefore has a very marked affect on acetaldehyde metabolism. A meta-analysis (Luczak et al. 2006) showed that subjects heterozygous for a null ALDH2 allele have only about one-fourth the risk for alcohol dependence as those with two functional alleles.
