A new study reveals why some people are able to recover from a traumatic event, while others develop post-traumatic stress disorder (PTSD).

Apparently, PTSD is much more likely to affect adults who experienced trauma in childhood, but variations of a certain gene raise the risk even more if the childhood trauma was related to physical or sexual abuse.

"Posttraumatic stress disorder (PTSD) is a debilitating stress-related psychiatric disorder, with prevalence rates of at least 7 percent to 8 percent in the U.S. population, and with much higher rates among combat veterans and those living in high-violence areas. Initially viewed as a potentially normative response to traumatic exposure, it became clear that not everyone experiencing trauma develops PTSD. Thus, a central question in research on PTSD is why some individuals are more likely than others to develop the disorder in the face of similar levels of trauma exposure," the authors of the study wrote, according to Science Daily.

The research was carried out by scientists at Emory University and the results were published in the Journal of the American Medical Association.

The results revealed that, among adults who suffered severe abuse in childhood, those who showed gene variations had the post-traumatic stress level more than twice as high compared to the ones whose genes showed no variation.

The study, involving 900 adults, is one of the few to prove that genes can be influenced by outside factors. The subjects of the research were chosen from impoverished environments. They were mostly African-American aged from 18 to 81 and most of them had suffered severe traumatic experiences in childhood, followed by other kinds of trauma in adulthood.

The gene that controls stress hormones is called FKBP5 and the protein it produces helps cells receptors detect stress hormones.

The study shows once more that severe abuse that happens very early in life can lead to profound traumas in adulthood.