The current study was guided by two primary aims. The first was to estimate heritability of PTSD in young women, using a large (n=3768) community-based sample. This is itself a unique contribution to the literature, as the one known twin study addressing PTSD that included women was based on only 812 twins (25 % of whom were male) and examined symptoms rather than the full PTSD diagnosis (Stein et al. 2002). Our second aim was to test for common genetic influences on PTSD and AD in women after accounting for possible heritable influences on trauma exposure. Given the gender differences in rates of exposure to various types of trauma, conditional probability of developing PTSD following trauma exposure (Resnick et al. 1993; Breslau et al. 1998; Hapke et al. 2006), and prevalence of AD (Holdcraft & Iacono, 2002; Hasin et al. 2007; Keyes et al. 2008), patterns of heritable influences may differ considerably from what has been observed in combat-exposed males.
