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

The role of genetic and environmental influences on the relationship between combat exposure, posttraumatic stress disorder (PTSD) symptoms, and alcohol 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 the relationship between combat and alcohol use and between PTSD symptom factors and alcohol use were both substantially influenced by genetic factors. Findings are most consistent with a shared vulnerability model for the etiology of the association between PTSD symptoms and alcohol use. Specific unique environmental factors were more important than genetic factors for PTSD symptoms, and both factors were equally important for alcohol use. Further support is also found for the role of the unique environment in PTSD symptoms.