Tests of a direct effect of childhood abuse on adult borderline personality disorder traits: a longitudinal discordant twin design

Abstract

We used a longitudinal twin design to examine the causal association between sexual, emotional, and physical abuse in childhood (before age 18) and borderline personality disorder (BPD) traits at age 24 using a discordant twin design and biometric modeling. Additionally, we examined the mediating and moderating effects of symptoms of childhood externalizing and internalizing disorders on the link between childhood abuse and BPD traits. Although childhood abuse, BPD traits, and internalizing and externalizing symptoms were all correlated, the discordant twin analyses and biometric modeling showed little to no evidence that was consistent with a causal effect of childhood abuse on BPD traits. Instead, our results indicate that the association between childhood abuse and BPD traits stems from common genetic influences that, in some cases, also overlap with internalizing and externalizing disorders. These findings are inconsistent with the widely held assumption that childhood abuse causes BPD, and they suggest that BPD traits in adulthood are better accounted for by heritable vulnerabilities to internalizing and externalizing disorders.

Figure 1. Visual Representation of Cholesky Decomposition

Note: CA, Childhood abuse; BPD, Borderline personality disorder traits; A = additive genetic influences; C = shared environmental influences; E = non-shared environmental influences. In this model, path a32 and path e32 is the path of interest (coefficients for these paths are reported in Table 6). This path shows the regression effect of CA on BPD traits after adjusting for EXT. The same model is used to adjust for the effect of INT or INT-EXT.

Figure 2. Within Twin Pair Differences in BPD Trait Scores for Pairs Discordant for Child Abuse

Note: CA, Childhood abuse; BPD, Borderline personality disorder traits. The BPD index was z-scored, and unstandardized regression weights [B (SE)] are presented above the bar.