Individuals with the atypical aldehyde dehydrogenase ALDH2 allele, both homozygous and heterozygous status, are alcohol sensitive and have a markedly reduced risk of developing alcoholic diseases. Genetic abnormalities of the ALDH1 locus are also associated with alcohol flushing. The ALDH3 and ALDHx loci are polymorphic and their variations may affect the development of alcoholic diseases. The variations of alcohol dehydrogenase ADH2 and ADH3 loci have no profound effects on alcohol sensitivity. The newly identified ADH6 gene has hormone response elements, and it may cause the gender difference in alcoholic problems.