Genetic covariance structure of the four main features of borderline personality disorder

Abstract

The patient population of borderline personality disorder (BPD) is heterogeneous; many different combinations of BPD symptoms can lead to a BPD diagnosis. We investigated to what extent the covariance among four main components of BPD is explained by shared genetic and environmental factors. Using an extended twin design, multivariate genetic models were applied to the scales of the PAI-BOR, a self-report questionnaire tapping four main features of BPD (affective instability, identity problems, negative relationships, and self-harm). Data on the four BPD scales were available for 5,533 twins and 1,202 siblings from the Netherlands, Belgium, and Australia. The correlations among the scales ranged from 0.23 to 0.50 and were best explained by a genetic common pathway model. This model specifies that genes and environment influence the covariance between four main features of BPD in qualitatively similar ways, through a single latent factor representing the BPD construct. The heritability of the latent BPD factor was 51% and the remainder of its variance was explained by unique environmental influences. For each BPD scale, except self-harm, around 50% of its variance was explained by the latent BPD factor. The remaining variance for each of the four scales was explained by genetic (4% for affective instability to 20% for self-harm) and environmental (38% for negative relationships to 67% for self-harm) factors that were specific to each scale.

FIGURE 1

Graphical representations of the Cholesky, independent pathway and the common pathway models. AI = affective instability; IP = identity problems; NR = negative relationships; SH = self harm; BPD = borderline personality disorder; A1 through A4 = additive genetic factors, E1 through E4 = unique environmental factors, A_c = additive genetic factor common to multiple traits; E_c = unique environmental factor common to multiple traits; A_s = specific genetic factors; E_s = specific unique environmental factors; a, e, and f = factor loadings; k = latent factor A or E; j = phenotype AI, IP, NR, or SH. All latent A and E factors have unit variance.

FIGURE 2

Graphical representation and path coefficients (95% confidence intervals) of the independent pathway model and the common pathway model. AI = affective instability; IP = identity problems; NR = negative relationships; SH = self harm; BPD = borderline personality disorder; A_c = genetic factor common to multiple traits; E_c = unique environmental factor common to multiple traits; A_s = specific genetic factors; E_s = specific unique environmental factors. All latent A and E factors have unit variance.