The ADH1B and ALDH2 polymorphisms are ancient, occurring on characteristic and highly diverged haplotypes. It is unlikely that either generic variant was selected to high frequency to reduce the likelihood of alcoholism after the introduction of alcohol into these populations, which probably occurred well after the spread of the polymorphisms. It has been hypothesized that Arg48 and/or Lys487 were selected to high frequencies in East Asian populations because they alter susceptibility to protozoal infections of the gut, including amebiasis.60 These infections are sometimes treated with metronidazole, which potently inhibits aldehyde dehydrogenase.60
