The presence of even a single ALDH2*2 allele is strongly protective against alcohol dependence. In fact, the protective effect of ALDH2*2 is the most widely reproduced association of a specific gene with alcoholism (Chen et al. 1999a; Hurley et al. 2002; Luczak et al. 2006; Thomasson et al. 1991). Compared with a Chinese man carrying two active ALDH2*1 alleles and the two copies of the normal ADH1B*1 allele, the odds ratio for risk for alcoholism for a Chinese man carrying one inactive ALDH2*2 allele and two ADH1B*1 alleles is 0.33. If, in addition to the ALDH2*2 allele, the man also carries at least one overactive ADH1B*2 allele, the odds ratio declines even further, to 0.05 (Chen et al. 1999a). In people homozygous for ALDH2*2, the effects of small amounts of alcohol are even more severe (Chen et al. 1999b; Peng et al. 1999), and there are almost no documented cases of such people being diagnosed as alcoholic (Chen et al. 1999b; Luczak et al. 2006). The severe effects of the ALDH2*2 variant on acetaldehyde levels and alcoholism risk demonstrate that
