Differences could also be attributable to bias secondary to ascertainment of the sample on the basis of twins’ self-report of CSA or CPA. To address this possibility, we examined whether similar relationships between MDD and low- and high-risk trauma are found in the full community-ascertained cohort II sample (PTSD was not assessed) (see eTables 5 and 6 and eFigure 2). We found a somewhat higher estimated heritability of MDD (37%) and a slightly lower value for low-risk trauma (40%). The value for high-risk trauma was nearly identical (61%) to the value estimated in the main sample. A slightly lower genetic correlation for MDD and high-risk trauma was observed (0.72), whereas the genetic correlation for the 2 trauma types (0.56) was similar to that found in the main sample (0.52). Overall, the results of these supplementary analyses suggest that ascertainment bias had very limited effect on these findings. Thus, these findings provide evidence that low-risk trauma exposure is moderately heritable and that there is considerable overlap in genetic factors that influence high- and low-risk trauma exposure.
