Unique Features of Peer Relationships in Specific Developmental Periods Predict Borderline Personality Disorder vs. Major Depressive Disorder in Late Adolescence

It is well established that peer relationships and psychopathology reciprocally influence each other across development, but it is less clear how different trajectories of peer functioning are associated with specific psychiatric disorders. To better understand how such trajectories might differentially predict risk for two debilitating diagnoses – borderline personality disorder (BPD) and major depressive disorder (MDD) - thecurrent study explored how bullying victimization, peer acceptance, and relational aggression, measured repeatedly across two distinct developmental periods, namely ages 3-8 (early childhood) and ages 9+ (middle childhood-adolescence), might individually and in combination predict BPD and MDD symptoms in adolescence. Elevated relational aggression in early childhood uniquely predicted greater adolescent BPD symptoms, whereas sustained peer acceptance from middle childhood through adolescence protected males against adolescent MDD, highlighting the need for timing- and sex-specific screening and prevention.