Biological factors associated with susceptibility to posttraumatic stress disorder.

Because only a proportion of persons exposed to traumatic events develop posttraumatic stress disorder (PTSD), it has become important to elucidate the factors that increase the risk for the development of PTSD following trauma exposure as well as the factors that might serve to protect individuals from developing this condition. Putative risk factors for PTSD may describe the index traumatic event or characteristics of persons who experience those events. Recent data have implicated biological and familial risk factors for PTSD. For example, our recent studies have demonstrated an increased prevalence of PTSD in the adult children of Holocaust survivors, even though these children, as a group, do not report a greater exposure to life-threatening (Diagnostic and Statistical Manual of Mental Disorders [DSM-IV] Criterion A) events. These studies are reviewed. It is difficult to know to what extent the increased vulnerability to PTSD in family members of trauma survivors is related to biological or genetic phenomena, as opposed to experiential ones, because of the large degree of shared environment in families. In particular, at-risk family members, such as children, may be more vulnerable to PTSD as a result of witnessing the extreme suffering of a parent with chronic PTSD rather than because of inherited genes. But even if the diathesis for PTSD were somehow "biologically transmitted" to children of trauma survivors, the diathesis is still a consequence of the traumatic stress in the parent. Thus, even the most biological of explanations for vulnerability must at some point deal with the fact that a traumatic event has occurred.