Adults exposed to abuse as children are at greater risk for Post Traumatic Stress Disorder, or PTSD, as adults, according to a study released this week in the Journal of the American Medical Association.

PTSD is a debilitating stress-related psychiatric disorder triggered by trauma. Rates are highest among war veterans and people living in high-crime areas.

The 900 low-income urban people surveyed reported multiple traumatic events over the course of their lives. Study co-author Rebekah Bradley, assistant professor of Psychiatry at Emory School of Medicine says that more than 40 percent said they had been exposed to four or more different types of traumatic events. "This would be a natural disaster, a car accident, a friend or family member who had been murdered and some other kind of assault."

But not everyone exposed to trauma develops PTSD, and the researchers wanted to find out why. They studied three factors: childhood sexual and physical abuse, other types of trauma and genetic factors.

Thirty percent of the people in the study reported a history of child abuse. Those who had later also experienced other traumas had twice the number of PTSD symptoms as the adults who were not abused as children.

But a history of abuse was not enough to explain increased PTSD symptoms among adults. DNA was analyzed to determine whether certain variations of a stress-related gene were present or not. Bradley says four of those variations showed a significant interaction with childhood abuse in predicting post-traumatic stress disorders.

The gene in question is called FKBP5. It normally helps regulate stress in the body, igniting a normal fear-related response under trauma and later shutting it down. Bradley says Post Traumatic Stress Disorder itself was found to be associated with problems in that stress response system.

PTSD is usually treated with psychotherapy and drugs. Bradley says the new discovery may lead to strategies that might help better manage the condition. "This finding is consistent with the idea that PTSD is related to alterations in our stress response system and that treatments themselves for the stress response system are going to be effective." Bradley adds that it may also provide a clue of how to best target medicines where the stress response is altered.

The study is part of this week's special issue of the Journal of the American Medical Association devoted to the influence of genes on health and disease.