Although the pattern of internalizing scores by risk group was consistent with expectations assuming genetic transmission from parental alcoholism, differences between groups were small and mostly nonsignificant. Compared to offspring of control twins, offspring of an alcoholic parent exhibited greater internalizing behavior; however, offspring of an alcoholic parent were indistinguishable from offspring at low environmental risk but high or intermediate genetic risk, who were in turn indistinguishable from offspring of control twins. In contrast, offspring of an alcoholic parent and offspring of an unaffected parent at high genetic risk exhibited similar levels of externalizing, with both groups exhibiting greater externalizing than offspring at intermediate genetic risk or offspring of control twins. The same pattern was observed for a measure of total problem behavior.
