However, people with the same history of trauma exposure (or exposure to other environmental risk factors) may differ in their risk of psychiatric disorder (e.g., depression) because of differences in genetic vulnerability (Sullivan et al. 2000). In other words, it is plausible that GxE interaction effects play an important role in determining risk. Because genetic factors contribute to the risk of alcohol dependence, offspring of alcohol-dependent parents will also inherit an increased genetic risk of alcohol dependence. Thus, in the presence of intergenerational processes such as those modeled in the figure, one would expect to observe increased rates of other psychiatric disorders in those with alcohol dependence, even if there were no direct effect of the comorbid disorders on risk of alcohol dependence. This is because alcohol-dependent people in addition to their genetic predisposition on average also are more likely to have experienced high-risk environmental exposures associated with parental alcoholism. These high-risk exposures, by interacting with genetic risk factors for other psychiatric disorders, will have increased the person’s risks of other psychopathology. In such instances where comorbid disorders do not
