Mutualistic Processes in the Development of Psychopathology: The Special Case of Borderline Personality Disorder

Borderline personality disorder (BPD) is a serious mental illness characterized by instability in affective, cognitive, and interpersonal domains. BPD co-occurs with several mental disorders and has robust, positive associations with the general factors of psychopathology (p-factor) and personality disorders (g-PD). Consequently, some researchers have purported BPD to be a marker of p, such that the core features of BPD reflect a generalized liability to psychopathology. This assertion has largely stemmed from cross-sectional evidence and no research to date has explicated the developmental relationships between BPD and p. The present study aimed to investigate the development of BPD traits and the p-factor by examining predictions of two opposing frameworks: dynamic mutualism theory and the common cause theory. Competing theories were evaluated to determine which perspective best accounted for the relationship of BPD and p from adolescence into young adulthood. Data were drawn from the Pittsburgh Girls Study (PGS; N = 2,450) and included yearly self-assessments of BPD and other internalizing and externalizing indices from ages 14 to 21. Theories were examined using random-intercept cross-lagged panel models (RI-CLPMs) and network models. Results indicated that neither dynamic mutualism nor the common cause theory could fully explain the developmental relations between BPD and p. Instead, both frameworks were partially supported, with p found to strongly predict within-person change in BPD at several ages.