By Olivia Trani 

Nearly 7 in 10 people will experience or witness at least one traumatic event in their lifetime, such as physical or sexual assault, motor vehicle accident, or natural disaster. While exposure to trauma often leads to intense feelings and emotional distress, most people recover with time and treatment.

However, for some, these feelings can linger – or even worsen – for months or years. Symptoms of this mental health condition, known as post-traumatic stress disorder (PTSD), can include flashbacks, nightmares, severe anxiety, and uncontrollable thoughts about the event. This can disrupt a person’s ability to function in daily life and sometimes even lead to long-term mental and physical health issues.

Women are more than twice as likely as men to develop PTSD, but the factors contributing to this disparity have largely remained unsettled. A research team led by Virginia Commonwealth University and Lund University in Sweden conducted the largest twin-sibling study of PTSD to date to shed light on how genetics may play a role.

Their results, published earlier this year in the American Journal of Psychiatry, are the first to demonstrate that women have a higher genetic risk for the disorder compared with men. The researchers say their findings could inform strategies for PTSD prevention and intervention following a traumatic event, as well as help address stigmas related to women’s mental health.

“Some of the theories as to why PTSD is more prevalent in women have frankly been unkind, such as attributing the sex difference to a weakness or lack of ability to cope,” said  Ananda B. Amstadter, Ph.D., a professor in the VCU School of Medicine’s departments of Psychiatry and Human and Molecular Genetics and lead author of the study. “I think this study can help move the narrative that people can have an inherited biological risk for PTSD, and that this genetic risk is greater in women.”

VCU Health News spoke with Amstadter to learn more about PTSD and how the genes we inherit from our parents impact our risk for developing this condition. 

How prevalent is PTSD and how does risk vary between women and men? 

Even though most people will undergo some form of trauma in their lifetime, only about 6% of those who are exposed to a traumatic event end up developing PTSD. Women are more than twice as likely to develop PTSD, even when controlling for the type of trauma, income level, social support and other environmental factors, but there hadn’t been conclusive evidence into why that is.

What do we know about the factors that can influence a person’s risk of developing PTSD after a traumatic event? 

My research focuses on trying to better understand the factors that can put a person more at risk of developing PTSD following a trauma and what factors make a person more resilient.

If you think of risk for PTSD like a pie chart, we’re trying to figure out what factors make up the pieces of this pie, as well as how big or small each piece is. Some of the risks are influenced by a person’s environment, such as the types of experiences, relationships, and support systems they have while growing up. On the other hand, some of the risk will be influenced by the genes they inherit from their parents.

In this latest study, we wanted to find out how much of an influence genetic and environmental factors have on a person’s risk of developing this disorder, and how that might differ by sex.

How did you go about trying to find these answers? What did your study reveal about genetic risk for PTSD?

Twin studies are one of the main ways that researchers gain insights into the heritability of traits, characteristics, and medical conditions. By comparing the genetic similarities between identical and fraternal twins, we can make estimates on how their genes influence their risk for mental illnesses like PTSD.

For this project, we conducted the largest twin-sibling study of PTSD to date by collaborating with researchers at Lund University in Sweden, who have access to anonymized clinical data for the entire population of Sweden. Every time a person interacts with Sweden’s health care system, whether that’s visiting their primary care doctor, filling a prescription, or going to the hospital, that information is recorded in their national registries.

By analyzing data from more than 400,000 pairs of twins or siblings born within two years of each other, we discovered that the heritability of PTSD was 7 percentage points higher in women than men (35.4% vs. 28.6%). This essentially means that, when considering the factors that influence the risk of PTSD, genetics plays a bigger role in women compared to men.

We also discovered that the genes linked with PTSD were highly correlated (0.81) but not entirely the same between men and women. This means that, while most of the genes associated with PTSD can be found in both men and women, some of those genes are likely specific to a person’s sex. We are now working with the Psychiatric Genomics Consortium to try to identify all of the molecular genetic variants that account for this difference in heritability.

How do these findings impact our understanding of PTSD, as well as prevention and treatment for this condition?

Our study demonstrated for the first time that woman have a greater inherited biological risk for PTSD compared to men. Having a higher genetic risk for PTSD does not make it a person’s destiny by any means, but understanding your family history of the disorder could help clinicians assess whether preventative services should be considered following a traumatic event.