PTSD vulnerability, damage explored in twin study

Post-traumatic stress disorder may stem from a combination of pre-existing vulnerability to stress and damage to the brain caused by exposure to a traumatic event, Boston researchers say based on studies of Vietnam veterans and their identical twins.

Some brain abnormalities have been found in people with PTSD, but researchers haven't known whether they were signs of PTSD or risk factors for it. Dr. Roger K. Pitman and his colleagues from Massachusetts General Hospital and the VA Medical Center in Manchester, NH., tried to answer the question by studying 130 combat veterans and their twins who had not seen combat. They present their findings today at a meeting of the American College of Neuropsychopharmacology.

Neurological exams and MRIs showed that the combat veterans had more mental problems than their brothers, but both twins also shared some impairments in neurological function, including problems related to the part of the brain critically involved in the fear response.

The combat veterans showed other brain changes -- atrophy in an area linked to decision making -- that their twins did not have. Researchers suggested that a stressful psychological event, or the stress of having PTSD itself, was responsible for the difference.

"We have identified several abnormalities that combat veterans share with their combat-unexposed twins that must represent risk factors. They could not have been acquired as a result of combat since their twins also have them," Pitman said in a conference call with reporters. But "traumatic stress can alter both brain structure and brain function. Our findings tend to refute the suggestion that people with PTSD would have probably had [psychological symptoms] even if they hadn't been exposed to a traumatic event."