Why are some people able to recover from the trauma of a violent attack or combat zone, while others suffer from recurrent flashbacks, episodes of depression and other debilitating symptoms of post-traumatic stress disorder (PTSD)?
To get a better understanding, scientists led by Dr. Kerry Ressler from Emory University conducted a study of 64 traumatized patients — in this case civilian patients at Atlanta’s Grady Memorial Hospital, not combat veterans. The researchers focused on a particular hormone-like molecule called PACAP (pituitary adenylate cyclase-activating polypeptide), which is known to affect response to stress on the cellular level. They found that patients who suffered from PTSD had higher levels of PACAP than patients without the psychiatric disorder. What’s more, the higher the patients’ blood levels of PACAP, the more severe their PTSD symptoms. (More on Time.com: Playing Tetris to Prevent PTSD Flashbacks)
But when the researchers split the data by gender, they found that the association between PACAP and PTSD was significant only in women. So the scientists designed a follow-up study with 74 traumatized female patients at the same hospital.
Reported ABC News:
Again, PACAP levels correlated with PTSD symptoms — especially those considered essential for a diagnosis of PTSD: intrusive flashbacks, avoidance of trauma reminders and increased startle response.
“These data may begin to explain sex-specific differences in PTSD diagnosis, symptoms and fear physiology,” Ressler and his colleagues wrote in their report, published [Wednesday] in Nature.
Women are known to have a higher risk of a range of anxiety disorders. But the finding of elevated PACAP in women with PTSD did more than offer a biological explanation for the gender difference; it pointed to a novel biological pathway underlying the brain’s response to fear.
Ressler and his team then looked at the genes that code for PACAP and its receptor, PAC1. They found that women with PTSD were not only more likely to have high levels of PACAP, but were also more likely to have a variation to a gene for PAC1 that also responds to estrogen. That variation — which increased PAC1 sensitivity to both estrogen and stress — was not found in the gene itself but instead in the epigenome. Such epigenetic changes are acquired over time, through environmental influences — suggesting that people who are not genetically hardwired to be vulnerable to PTSD may become vulnerable through experience.
Ressler replicated the association in additional 439 patients; again it was found in women, but not men. The findings could point to new ways to identify people who may be especially susceptible to PTSD. If confirmed in larger groups, the discovery could even lead to more targeted and effective treatment possibilities. (More on Time.com: Many Youth Offenders Have History of Traumatic Brain Injury)
PTSD can be hard to treat and may cause lasting symptoms, including panic disorder, depression and even suicide. “In a lot of very impoverished, high-violence neighborhoods, we see high rates of trauma, and rates of PTSD can be as high as in veterans,” Ressler told ABC News.