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

TLDR

The study aimed to determine how heredity, shared environment, and unique environment affect liability for 15 self‑reported PTSD symptoms among Vietnam‑era veteran twin pairs. The authors analyzed 4042 monozygotic and dizygotic male twin pairs, assessing genetic and environmental contributions to PTSD symptom liability across reexperiencing, avoidance, and arousal clusters. Quantitative genetic analysis shows that inheritance substantially influences all PTSD symptom clusters, with genetic factors accounting for 13–34 % of liability variance, while shared environment has no effect and combat exposure is strongly linked to reexperiencing and avoidance symptoms.

Abstract

• 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.