With respect to alcoholism, researchers have used the candidate gene approach to investigate the association between certain ADH and ALDH alleles and an altered risk of alcoholism. Studies have found that the enzyme encoded by an ALDH allele called ALDH2*2 degrades acet aldehyde more slowly than normal, resulting in the prolongation of certain unpleasant alcohol effects, such as facial flushing, racing of the heart (i.e., palpitations), and nausea. Not surprisingly, this allele appears to have a protective effect against alcoholism—that is, people carrying the allele are less likely to consume alcohol and to develop alcoholism (for a review, see Reich et al. 1999). The frequency of the ALDH2*2 allele is particularly high in some Asian populations, and carriers of this allele consume less alcohol and are much less likely to develop alcoholism than are people without the allele.
