April 1993

A Twin Study of Genetic and Environmental Contributions to Liability for Posttraumatic Stress Symptoms

Author Affiliations

From the School of Public Health and Department of Psychiatry, St Louis University Medical Center, and the Health Services Research and Development Program, Veterans Affairs Medical Center, St Louis, Mo (Dr True); Departments of Psychiatry (Drs Rice and Heath and Ms Nowak), Psychology (Dr Heath), and Genetics (Dr Heath), Division of Biostatistics (Dr Rice), and Department of Medicine (Dr Eisen), Medical and Research Services, Veterans Affairs Medical Center, and the Washington University School of Medicine, St Louis, Mo; Hines Veterans Affairs Cooperative Studies Program Coordinating Center and Epidemiology Program, School of Public Health, University of Illinois, Chicago (Dr Goldberg); and Psychiatry Service, Veterans Affairs Medical Center, Brockton, Mass, and Department of Psychology, Boston (Mass) University (Dr Lyons).

Arch Gen Psychiatry. 1993;50(4):257-264. doi:10.1001/archpsyc.1993.01820160019002

• We studied 4042 Vietnam era veteran monozygotic and dizygotic male twin pairs to determine the effects of heredity, shared environment, and unique environment on the liability for 15 self-reported posttraumatic stress disorder symptoms included in the symptom categories of reexperiencing the trauma, avoidance of stimuli related to the trauma, and increased arousal. Quantitative genetic analysis reveals that inheritance has a substantial influence on liability for all symptoms. Symptoms in the reexperiencing cluster and one symptom in the avoidance and numbing cluster are strongly associated with combat exposure, and monozygotic pairs are more highly concordant for combat exposure than dizygotic pairs. By fitting a bivariate genetic model, we show that there are significant genetic influences on symptom liability, even after adjusting for differences in combat exposure; genetic factors account for 13% to 30% of the variance in liability for symptoms in the reexperiencing cluster, 30% to 34% for symptoms in the avoidance cluster, and 28% to 32% for symptoms in the arousal cluster. There is no evidence that shared environment contributes to the development of posttraumatic stress disorder symptoms.