A new study published in American Journal of Psychiatry revealed that women may be at a higher genetic risk of developing post-traumatic stress disorder (PTSD) compared to men. The study, led by researchers from Virginia Commonwealth University and Lund University, is the largest twin study of PTSD to date. The findings suggest that while both men and women are genetically predisposed to PTSD, the underlying genetic risk may be stronger in women.
Post-traumatic stress disorder is a psychiatric condition that occurs after experiencing or witnessing traumatic events. Individuals with PTSD often suffer from unpleasant symptoms such as flashbacks, nightmares, anxiety, and emotional numbing. While PTSD can affect anyone, studies have shown that women are twice as likely to develop the condition as men. Despite these differences, the reasons for the higher prevalence of PTSD in women remain unclear.
Many hypotheses have been proposed, including differences in trauma exposure, coping mechanisms, and biological factors. However, there is limited research that has investigated the genetic basis of these sex differences.
Previous studies have suggested that PTSD may have a genetic component, but have left a gap in understanding whether these genetic risks differ between men and women. In addition, earlier studies were often limited by small sample sizes or reliance on self-reported data, which may introduce bias. To address these gaps, the research team aimed to test whether genetic risk factors for PTSD differ between men and women using a large representative sample from Sweden.
“PTSD is an important disorder that has received less attention in genetic epidemiologic studies compared to other psychiatric disorders. “That’s why it was important to study estimates of heritability, the extent to which genes influence the risk of the disorder, and gender differences in the heritability of PTSD,” said Ananda B. Amstadter, a professor at Virginia Commonwealth University School of Medicine. of the Department of Psychiatry and Human and Molecular Genetics and the main author of the study.
For their study, researchers analyzed data from more than 16,000 twin pairs and more than 376,000 sibling pairs from the Swedish National Health and Population Registers. This large sample allowed them to examine both the genetic and environmental components 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 accessed health data from hospital records, outpatient care, and primary care clinics that included diagnoses of PTSD based on International Classification of Diseases (ICD) codes.
By using these registry-based medical diagnoses, the researchers avoided potential biases associated with self-reported data, such as memory errors or reporting inconsistencies. This gave their study a solid foundation for more accurate analysis.
To isolate the genetic factors that contribute to PTSD, the researchers used statistical models that compared different sets of twins and siblings. Monozygotic twins, who share 100% of their genes, were compared to fraternal twins and full siblings, who share about 50% of their genes. This allowed scientists to estimate the heritability of PTSD, which refers to the proportion of variation in PTSD risk that can be attributed to genetic differences.
“If you think of PTSD risk as a pie chart, we’re trying to better understand what factors make up the pieces of that pie,” Amstadter said. “Some risks are influenced by a person’s environment, for example, the experiences they have during adolescence. On the other hand, some risk will be influenced by the genes they inherit from their parents.”
The study’s findings showed 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 higher genetic risk of developing PTSD compared to 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 could explain part of the observed disparity in PTSD prevalence.
“PTSD has been found to be moderately heritable in both males and females,” Amstadter told PsyPost. “However, the heritability was significantly higher in women, meaning that the genetic risk of PTSD is higher in women compared to men. Furthermore, although the heritability between the sexes was essentially correlated, the findings suggest that some of the genes that contribute to the heritability of the sexes differ. This means that future research should focus on sex-specific pathways of risk for the disorder, 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 traumatic exposures—also played a significant role in the development of PTSD. These environmental factors accounted for most of the variance in PTSD risk in both 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 effect on the risk of PTSD. This suggests that while genetics and personal experiences are important, the general family environment does not appear to contribute much 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, particularly in women, may influence the development of PTSD by affecting the body’s stress response systems.
For example, estrogen has been shown to regulate genes involved in the stress response, and changes in estrogen levels during the menstrual cycle may make women more susceptible to stress-related disorders such as PTSD. Future studies could examine how these hormonal effects interact with genetic risk factors to increase or decrease the likelihood of developing PTSD.
Another area of ​​future research is investigating how genetic factors influence PTSD treatment responses. While trauma-focused therapies such as cognitive therapy are effective for both men and women, some studies suggest that women may respond better to these treatments than men. Understanding the genetic basis of treatment response could help personalize PTSD interventions and ensure that individuals receive the most effective treatment based on their unique genetic and environmental risk factors.
The study, “Testing Quantitative and Qualitative Sexual Effects in the Swedish National Twin Study of PTSD,” was written by Ananda B. Amstadter, Sara L. Lönn, Shannon Cusack, Jan Sundquist, Kenneth S. Kendler, and Kristina. Sundquist.
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