Attachment and Borderline Personality Features: The Mediating Roles of Hypomentalizing and Epistemic Mistrust.

Insecure attachment is a well-established risk factor for the emergence of borderline personality features (BPF), encompassing identity disturbance, affective instability, problematic interpersonal relationships and self-harming behaviours. From a mentalizing-based perspective, BPF may develop through the interplay of hypomentalizing, defined as a reduced capacity to understand and reflect on one's own and others' mental states, and epistemic mistrust (EM), the diminished capacity to trust communicated information. Both processes are shaped by attachment anxiety and avoidance. However, research investigating the mechanisms linking attachment to BPF remains limited. This study examined the parallel mediating roles of hypomentalizing and EM in the associations between attachment dimensions and BPF. Data were drawn from a large combined clinical and community sample of 1129 participants (291 men, 819 women, 17 transgender individuals and 2 categorized as 'other'; mean age = 32.88 years, SD = 10.90). Participants completed the Experiences in Close Relationships-Revised (ECR-R); the Reflective Functioning Questionnaire-54 (RFQ-54); the Epistemic Trust, Mistrust and Credulity Questionnaire (ETMCQ); and the Borderline Features Scale of the Personality Assessment Inventory (PAI-BOR). Parallel multiple mediation analyses indicated that both hypomentalizing and EM significantly mediated the relationships between (a) attachment anxiety and BPF and (b) attachment avoidance and BPF. Supplementary analyses showed that these pathways did not differ across diagnostic groups, but EM was expressed most strongly in those participants who met criteria for borderline personality disorder (BPD), where it differentiated the group from clinical (depression and anxiety disorders) and community comparisons. These findings support the theoretical basis for mentalization-based interventions, highlighting the importance of improving mentalizing and reducing mistrust in communication to foster adaptive social learning. Nonetheless, the cross-sectional design and reliance on self-report measures limit causal inference and introduce potential bias. Future research should employ longitudinal designs to further evaluate the proposed model.