At first reading, much of the existing literature on the role of genetic factors in the development of alcohol dependence and other disorders (e.g., depression), particularly twin and adoption studies, appears to provide little support for the importance of family environmental and GxE interaction effects. These studies have consistently concluded that genetic factors overwhelmingly account for the familial transmission of risk of both alcohol dependence (e.g., Heath et al. 1997) and other psychiatric disorders, such as depression (e.g., Sullivan et al. 2000). Three issues, however, need to be considered before accepting this interpretation.
