nt on the context of the other variables in the system" (8:223-229). Thus, it may be inaccurate to argue that there is or is-not a gene that causes alcoholism. The occurrence of genetic susceptibility to the disease is actually only one single aspect of its complete, multifactorial etiology.
Despite this scenario though, it is still probably fair to call alcoholism the most common human hereditary disease. References to its genetic tendencies can be found as far back as the writings ancient Greek and Chinese civilizations (3:145). More recently, adoption studies, twin studies, and investigations involving at-risk relatives of alcoholics have provided additional evidence for this contention. During the 1970s, for example, researchers showed that children of alcoholics who were adopted by nonalcoholics had a higher probability of becoming alcoholics themselves than did their step-siblings (7:29). These same studies showed that the sons of alcoholics exhibited characteristics such as less intense brain-wave activity and a higher alcohol tolerance--traits which could be inherited. Many years later, Carmelli et al. (1990) examined several thousand pairs of monozygotic and dizygotic male twins. He found significant heritability for average monthly alcohol consumption. Indeed, the heritability of alcoholism among Caucasians has been estimated to be as high as 50%. Lastly, Merikangas (1990) observed that first-degree relatives of persons suffering from the disease have a sevenfold increased risk for becoming alcoholics (6:232).
Because of both the etiologic complexity and the heterogeneity of the alcoholic condition, most researchers have presumed that several different genes are involved. Epistasis refers to "interaction among multiple genes" (10:347). With epistasis, a variant form of one gene cannot by itself cause a disease such as alcoholism. Instead, mutant alleles can only modify the gene expression of the group as a ...