Preschool Big Five Personality Traits Predict Childhood Peer Relationships and BPD but Not MDD in Late Adolescence.

Growing literatures highlight shared childhood predictors for future borderline personality disorder (BPD) and major depressive disorder (MDD). However, few longitudinal studies have examined both BPD and MDD as simultaneous outcomes. Childhood personality traits and poor peer relationships constitute transdiagnostic phenomena that could impact risk for later BPD and MDD. The current study examined whether school-age peer relationships mediated associations between preschool Big Five traits and adolescent BPD and/or MDD. Preschool Big Five traits were assessed through observational coding. School-age peer relationships were assessed via clinical interview, with separate child and parent reports. The Borderline Personality Features Scale for Children measured BPD symptoms in adolescence. The Kiddie Schedule for Affective Disorders and Schizophrenia (K-SADS) measured MDD symptoms in adolescence. Structural equation models with manifest composite variables were performed in a sample (n = 153) from the Preschool Depression Study, a prospective longitudinal study with assessments from preschool through adolescence. Lower preschool conscientiousness predicted adolescent BPD. Lower preschool conscientiousness also predicted poorer school-age peer relationships. In MDD models, preschool agreeableness and conscientiousness predicted better parent-reported school-age peer relationships, but not adolescent MDD. Mediation was not significant in the BPD or MDD models. This study identified preschool conscientiousness as one important factor relating to school-age peer relationships and future BPD, but not MDD. Our findings suggest that these pathways may be unique to BPD development and highlight the need for additional research targeting early personality and peer processes.