Content area
Full text
Although epidemiological studies reveal that the majority of individuals have been exposed to at least one potentially traumatic event (PTE) during their lifetime, a minority of trauma-exposed individuals develop posttraumatic stress disorder (PTSD).1 Genetic research has the potential to inform our understanding of why some individuals are vulnerable and others resilient to the effect of PTEs. This article provides an overview of genetic factors in the etiology of PTSD, with a focus on how our understanding of underlying neurobiologic alterations in patients with PTSD2 should inform future research in this area.
PTSD IS HERITABLE
If genetic factors play an etiological role in PTSD, family members of individuals with PTSD should have a higher prevalence of PTSD than similarly trauma-exposed family members who did not develop PTSD. This pattern has been shown in trauma-exposed adult children of Holocaust survivors; specifically, adult children of survivors with PTSD were more likely following trauma exposure to develop PTSD than were adult children of survivors without PTSD.3 This familial association has also been found in Cambodian refugees.4 However, be- cause family members frequently share important environmental influences, family studies cannot tell us whether a disorder runs in families for genetic or environmental reasons. Twin studies have been used to distinguish between genetic and environmental contributions to risk for PTSD.
Twin studies have made three important contributions to our understanding of the genetic etiology of PTSD. First, and perhaps most notably, they indicate that genetic factors influence exposure to PTEs. This is referred to as gene-environment correlation, whereby selection of environment, and subsequently potential for exposure to trauma, is partly determined by genetic factors.5 For example, twin studies have demonstrated that genetic factors influence exposure to PTEs. Lyons et al6 included members of the VET and studied variables indicative of war-related trauma (eg, volunteering for service in Southeast Asia, service in Southeast Asia, combat exposure, being awarded a combat medal). Heritability estimates ranged from 35% for Southeast Asia service to 54% for being awarded a combat medal. Additionally, a civilian study found evidence for a gene-environment correlation for assaultive violence.7 Second, twin studies suggest genetic influences explain a substantial proportion of vulnerability to PTSD even after accounting for genetic influences on PTE exposure. An early examination of the VET Registry reported...