Testing Quantitative and Qualitative Sex Effects in a National Swedish Twin-Sibling Study of Posttraumatic Stress Disorder

Twin studies have demonstrated that posttraumatic stress disorder (PTSD) is moderately heritable, and the pattern of findings across studies suggests higher heritability in females compared with males. Formal testing of sex differences has yet to be done in twin studies of PTSD. The authors sought to estimate the genetic and environmental contributions to PTSD, and to formally test for sex differences, in the largest sample to date of both sexes, among twins and siblings.