Genetics may play a major role in how likely a person is to develop post-traumatic stress disorder after experiencing a traumatic event, according to a new U.S. study.

The report, published Tuesday in the scientific journal Molecular Psychiatry, looked at more than 200 billion pieces of genetic information from more than 20,000 adults across the globe.

Researchers found patterns in the data that showed people with PTSD tended to have the same versions of genes, while those without the disorder had different versions.

“And so we were able to show that it is partly genetic,” first author Laramie Duncan from Stanford University told CTV News Channel on Tuesday.

That genetic link appears stronger among women, researchers found. In American women from European backgrounds, researchers found that 29 per cent of the risk for developing PTSD came from genetic factors.

In men, the genetic risk for developing PTSD was generally lower.

“We don’t actually understand why that is yet,” Duncan said. “For a lot of different medical conditions, it seems like the genetic influence on women is a little bit stronger than it is for men.”

The study lends scientific weight to earlier, small-scale research on twins that suggested a link between a person’s hereditary make-up and their likelihood of developing the debilitating condition.

PTSD is triggered by a traumatic event and lasts at least one month, but can remain for years. Patients with the disorder report reliving their trauma, having trouble sleeping, avoiding things that remind them of their trauma and becoming upset without any clear risk. It can also lead to higher rates of suicide, alcohol abuse and hospitalization.

More than 800,000 Canadians are estimated to have PTSD, and about 9 per cent of people who experience a traumatic event develop the disorder.

Researchers also found that people with higher genetic risk for several mental disorders – such as schizophrenia and bipolar disorder – also demonstrated a higher genetic risk for developing PTSD.

The new information could help health care providers identify PTSD faster and provide necessary treatment, such as talk therapy and medication, when patients need it most.

“We have interventions that help people not develop PTSD after they experience trauma, but they’re too expensive to use on everyone. And probably one of the first uses of genetic information like this is it could help us understand who might respond best to those treatments,” Duncan said.