(both alcoholic and nonalcoholic members) for the presence of the disease, also have provided convincing evidence that the risk for alcohol dependence is determined partly by genetic influences (Gelernter and Kranzler 2009). Overall, family, adoption,3 and twin studies provide convergent evidence that hereditary factors play a role in alcohol dependence, with variations in genes estimated to account for 50 to 60 percent of the total variance in risk. These estimates suggest that although genetic factors are important, nongenetic factors also contribute significantly to the risk for alcohol dependence.
