These gene variations have been selected for in different populations. For example, the ALDH2*2 variant is common only among people from east Asia, the ADH1B*2 variant is common among people from east Asia and the Middle East, and the ADH1B*3 variant is common in people from Africa (Edenberg 2007; Eng et al. 2007; Li et al. 2007, 2009). All of these variations have strikingly strong effects on risk; thus, in Asian populations, ALDH2*2 and ADH1B*2 each can lower risk by two- to sevenfold. No other known gene variations have such a strong effect on risk for alcoholism.
