Several lines of evidence demonstrate a substantial genetic component in the risk to developing alcohol dependence. Siblings of alcoholic probands have a 3- to 8-fold increase in the risk of also developing alcohol dependence (Reich et al., 1998). The heritability of risk for alcohol dependence is estimated to be ~39% by studies of the adopted-away offspring of affected and unaffected parents (Cloninger et al., 1981) and as high as 60% by twin studies (Heath et al., 1997). These studies provided evidence that genetic factors constitute a significant cause of alcohol dependence.
