In the largest study of its kind, researchers uncovered significant genetic and environmental influences on posttraumatic stress disorder, revealing notable sex differences in heritability.
The study, published in The American Journal of Psychiatry, conducted using data from the Swedish National Registries, included 16,242 twin pairs and 376,093 sibling pairs to estimate genetic and environmental contributions to posttraumatic stress disorder (PTSD) and to formally test for sex differences.
Key Findings
- Heritability differences: Heritability of PTSD was significantly greater in females (35.4%) than in males (28.6%), indicating a quantitative sex effect.
- Genetic correlation: The genetic correlation for PTSD between sexes was high but not complete (rg=0.81), suggesting qualitative sex differences.
- Environmental factors: Unique environmental effects, but not shared environments, significantly contributed to PTSD in both males and females.
Study Methodology
- Data Sources: Researchers linked nationwide Swedish registers, including the Swedish Twin Registry and the Multi-Generation Register, using diagnostic codes from medical registries.
- Sample: The study population included Swedish-born males and females between 1955 and 1980 with zygosity determined through standard self-reported items for twins.
- Measures: PTSD diagnoses were identified using ICD-9 and ICD-10 codes from hospitals, outpatient care, and primary health care settings.
Modeling Approach
- Researchers employed structural equation modeling to decompose genetic and environmental variance for PTSD and test for sex differences.
- The best-fit model indicated that additive genetic and unique environmental effects contributed to PTSD, with no evidence of shared environmental or special twin environment effects.
Implications
- This study provided the first formal demonstration of both quantitative and qualitative sex effects for PTSD.
- Findings suggested genetic influences are stronger in females, while unique environmental factors play a critical role in the disorder's development.
- Understanding the differential genetic and environmental contributions to PTSD can inform targeted interventions and treatments, particularly for sex-specific strategies.
The authors reported no financial relationships with commercial interests.