These findings support that the ALDH2 504lys allele can greatly lower the risk for AD as well as alcohol-induced diseases in the Asian populations. The reduction in ALDH2 activity in the 504lys/504glu heterozygotes is more than 100-fold compared with the ALDH2 activity of the 504glu/504glu homozygotes (Brooks et al. 2009; Crabb et al. 2004). Studies on liver extracts demonstrated that the ALDH2 504lys allele was nearly dominant, and the heterozygous and 504lys/504lys homozygous has almost no detectable ALDH2 activity in the liver (Edenberg 2007). The inactive ALDH2 504lys allele occurred mainly in some Asian populations (with the nearly complete absence of homozygous lys504lys alcoholics), but its prevalence varied across these samples. For instance, the 504lys allele was less commonly found in some aboriginal Chinese populations (e.g., Ami, Atayal, Bunun, Elunchan, Mongolian, and Paiwan) compared with Han Chinese. Figure 6 and supplementary Table 7 show the 504lys allele frequencies of by location. Most alcoholics with inactive ALDH2 alleles were heterozygous; homozygous lys-lys was rarely found in the alcoholic subjects, although it was often observed in controls. As expected, the recessive model
