As with any gene that affects a person’s risk of developing a complex disease, however, the protective effect of the ALDH2*2 allele can be modulated by the environment. This was clearly demonstrated by Higuchi and colleagues (1994). These investigators found that between 1979 and 1992, the fraction of Japanese alcoholics carrying the ALDH2*2 allele increased from 2.5 to 13 percent, indicating that the allele’s protective effect declined over time. In this case, the cause of this reduced protection presumably is a sociological change toward more alcohol consumption in Japan.
