All of these VETR studies accounted for possible heritable contributions to trauma exposure, which may otherwise be misattributed to PTSD (Seedat et al. 2001; Afifi et al. 2010). Lyons et al. (1993) estimated heritability of combat exposure to be 47% in the VETR sample and Stein et al. (2002) found evidence for genetic contributions to assaultive (but not nonassaultive) trauma in their general population-based twin sample. An individual’s genetic composition clearly does not directly influence the likelihood of experiencing trauma, but may do so indirectly through heritable personality traits. Jang et al. (2003), for example, found a substantial genetic correlation between exposure to assaultive trauma and both juvenile antisociality and openness to new experiences. Thus, to accurately characterize the relative genetic and environmental influences on PTSD and the overlap of these influences on those that contribute to AD, trauma exposure must also be modeled.
