Genetic Influences on Alcoholism Risk: A Review of Adoption and Twin Studies
Heath, Andrew C., Alcohol Health & Research World
The tendency for alcoholism to run in families has long been recognized through controlled family studies beginning in the 1950's (Amark 1951; Bleuler 1955; Cotton 1979). Research findings have indicated that alcoholism can arise in families through genetic or environmental causes or through a mixture of both. Researchers have used two different strategies for determining the proportional contributions of genes and shared family environment to the development of alcoholism among family members: the adoption study and the twin study. The adoption study compares the risk of alcoholism in biological relatives with the risk in adoptive relatives of alcoholics (e.g., an adopted-away child of an alcoholic parent). In contrast, the twin study compares the risk of alcoholism in identical and fraternal pairs of twins reared in the same environment. Although studies of the genetic aspects of alcoholism have expanded to include molecular and animal sudies, it is helpful to reexamine adoption and twin evidence; both types of data are important bases for subsequent research on genetic influences on alcoholism. This article briefly summarizes and updates a recent review reanalyzing the major published studies on gender differences in the genetic contribution to alcoholism risk (Heath et al. in press). (For more information on the methodology of these types of research, see the related articles in the Tools of Genetic Research section, pp. 190-227.)
This article focuses on studies that have systematically used samples ascertained from birth or adoption records. Unfortunately, however, this review excludes several important studies (Gurling et al. 1994; Pickens et al. 1991; Caldwell and Gottesman 1991; McGue et al. 1992; Heath et al. 1994), because various technical issues place those studies beyond the scope of this review (for further details, see Heath et al. in press).
ADOPTION STUDY FINDINGS
A Pioneering Study
The first adoption-study evidence for an important genetic contribution to alcoholism risk was produced in Scandinavia. In Copenhagen, Denmark, Goodwin and colleagues (1973, 1974, 1977a,b) used official registries to identify biological parents who had histories of alcoholism and who had given up a child for early adoption by nonrelatives. The researchers used biological parents who had no known histories of alcoholism but who also had given up a child for early adoption as control subjects. Interviews were conducted with adult sons and daughters of both groups to determine the prevalence of alcoholism among them. The researchers speculated that if the genetic contribution to alcoholism were important, the rates of alcoholism should be higher in the adopted-away offspring of the alcoholic biological parents than in the adopted-away offspring of the control parents.
The investigators also identified a subset of biological parents who had given up one child for adoption but had reared a second child themselves. This subset could demonstrate the effects of environment on the children. If growing up in the environment of an alcoholic parent contributes significantly to alcoholism risk, this risk should be higher in the nonadopted sons and daughters of alcoholics, compared with the adopted-away sons and daughters.
According to the findings, 8.9 percent of the fathers and 1.6 percent of the mothers who gave their offspring up for adoption had been hospitalized for alcoholism. Heath and colleagues (in press) estimated that the proportion of all adults in the population of Copenhagen who were in the same age range as the biological parents and who had been hospitalized for alcoholism at some stage in their lives was 2 percent for men and 0.5 percent for women. These figures are almost certainly overestimates. Compared with what would be expected for the population as a whole, the lifetime prevalence of hospitalization for alcoholism is at least four times higher in the biological fathers and three times higher in the biological mothers of the children who were given up for adoption. …