Genetic and environmental influences on the relationship among combat exposure, posttraumatic stress disorder symptoms, and alcohol use

The role of generic and environmental influences on the relationship betwee n combat exposure, posttraumatic stress disorder (PTSD) symptoms, and alcoh ol use were examined in 4072 male-male twin pairs who served in the United States military during the Vietnam era (1965-1975). Results indicate that t he relationship between combat and alcohol use and between PTSD symptom fac tors and alcohol use were both substantially influenced by genetic factors. Findings are most consistent with a shared vulnerability model for the eti ology of the association between PTSD symptoms and alcohol use, Specific un ique environmental factors were more important than genetic factors for PTS D symptoms, and both factors were equally important for alcohol use. Furthe r support is also found for the role of the unique environment in PTSD symp toms.