New research published in American Journal of Psychology has revealed that women may be at a higher genetic risk of developing post-traumatic stress disorder (PTSD) than men. The study, led by researchers from Virginia Commonwealth University and Lund University, is the largest twin study of PTSD conducted to date. Research findings suggest that although both men and women are susceptible to PTSD, the genetic risk may be greater for women.
Post-traumatic stress disorder is a mental condition that occurs after experiencing or witnessing a traumatic event. People with PTSD often experience distressing symptoms such as flashbacks, nightmares, anxiety, and emotional numbness. Although PTSD can affect anyone, studies have shown that women are twice as likely as men to develop the condition. Despite this difference, the reasons for the prevalence of PTSD in women remain unclear.
Many hypotheses have been proposed, including differences in trauma exposure, coping mechanisms, and biological factors. However, there has been little research examining the genetic basis of these gender differences.
Previous studies suggested that PTSD may have a genetic component, but left a gap in understanding whether these genetic risks differ between men and women. Additionally, previous studies were often limited by small sample sizes or relied on self-reported data, which could introduce bias. To address these limitations, the research team aimed to test whether genetic risk factors for PTSD differ between men and women using a large, nationally representative sample from Sweden.
“PTSD is an important disease that has received little attention compared to other mental disorders in genetic epidemiologic studies. Thus, heritability estimates, that is, the degree to which genes influence the risk of the disease, and gender differences in the inheritance of PTSD were important to study ,” said Ananda B. Amstadter, a professor at the Virginia Commonwealth University School of Medicine. departments of Psychology and Human and Molecular Genetics and lead author of the study.
For their study, researchers analyzed data from more than 16,000 twin pairs and more than 376,000 pairs from national health and population registries. This large sample allowed them to examine both the genetic and environmental aspects of PTSD in a way that previous studies, with smaller sample sizes, could not.
The researchers gathered their data from several Swedish national registries, including the Swedish Twin Registry, which provided information on twins, and the Multigeneration Registry, which tracked full siblings. They also obtained health data from hospital records, outpatient care, and primary care clinics, which included a diagnosis of PTSD according to the International Classification of Diseases (ICD).
By using this registration-based clinical trial, the researchers avoided potential biases associated with self-reported data, such as recall errors or inconsistent reporting. This gave their research a solid foundation for more accurate analysis.
To isolate the genetic factors that contribute to PTSD, the researchers employed statistical models that compared different sets of twins and siblings. Monozygotic twins, who share 100% of their genes, were compared to dizygotic twins and full siblings, who share about 50% of their genes. This allowed the researchers to estimate the heritability of PTSD, which refers to the proportion of variation in PTSD risk that can be attributed to genetic variation.
“If you think of PTSD risk as a pie chart, we’re trying to better understand what components make up the pieces of this pie,” Amstadter said. “Some risk is influenced by a person’s environment, such as the experiences they have while growing up. On the other hand, some risk will be influenced by the genes they inherit from their parents.”
The results of the study revealed that PTSD is moderately heritable, with genetic factors accounting for approximately 35% of the risk in women and 29% in men. This means that while both sexes inherit some genetic susceptibility to PTSD, the genetic contribution is stronger in women. This quantitative difference in heritability suggests that women have a greater genetic risk of developing PTSD than men, even after accounting for environmental factors.
Additionally, the study found evidence of qualitative differences in the genetic risk of PTSD between men and women. Although many of the same genes contribute to PTSD in both sexes, some genes appear to have sex-specific effects. This qualitative difference suggests that the genetic architecture of PTSD is not exactly the same in men and women, which may explain part of the difference seen in the prevalence of PTSD.
“PTSD appeared to have moderate heritability in both men and women,” Amstadter told PsyPost. “However, the heritability was greater in women, implying that the genetic risk for PTSD is greater in women compared to men. Furthermore, although heritability was significantly correlated between sexes, the results suggest that some genes contributing to heritability differ by gender This means that future research should focus on sex-specific risk pathways for the disease, which may have important implications for treatment.
In addition to genetic factors, researchers found that unique environmental experiences—such as individual life events or specific exposure to trauma—played an important role in the development of PTSD. These environmental factors contributed to significant differences in PTSD risk for men and women.
Interestingly, the researchers found no evidence that a shared family environment, such as growing up in the same household, had a significant influence on the risk of PTSD. This suggests that although genetics and personal experiences are important, the overall family environment does not appear to contribute significantly to the likelihood of developing PTSD.
One interesting direction for future research is to investigate the role of sex hormones, such as estrogen and testosterone, in PTSD. Previous studies have suggested that hormonal fluctuations, especially in women, may influence the development of PTSD by affecting the body’s stress response mechanisms.
For example, estrogen has been shown to regulate genes involved in the response to stress, and changes in estrogen levels during the menstrual cycle may make women more vulnerable to stress-related disorders such as PTSD. Future studies may examine how these hormonal effects interact with genetic risk factors to increase or decrease the likelihood of developing PTSD.
Another area for future research is to examine how genetic factors influence response to PTSD treatment. Although trauma-focused treatments, such as cognitive processing therapy, are effective for both men and women, some studies have suggested that women may respond better to these treatments than men. Understanding the genetic basis of treatment response can help personalize PTSD interventions, ensuring that people receive the best treatment based on their unique genetic and environmental risk factors.
The study, “Testing the Quantitative and Positive Effects of Sex in the Swedish National Twin Study of Posttraumatic Stress Disorder,” was written by Ananda B. Amstadter, Sara L. Lönn, Shannon Cusack, Jan Sundquist, Kenneth S. Kendler, and Kristina Sundquist.
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