PROJECT SUMMARY/ABSTRACT Borderline personality disorder (BPD) is a serious mental disorder associated with high cost that is transmitted intergenerationally. The interpersonal phenotype of BPD is characterized by hypersensitivity, hostile attribution bias, and maladaptive desire for exclusivity in relationships. Features of this phenotype can be identified in childhood and are associated with internalizing and externalizing pathology as well as later development of BPD. Aligned with the 2021 NIMH Strategic Plan, to identify malleable targets for prevention of psychopathology, it is necessary to study the unfolding of this critical mechanism prior to the onset of symptomatology. This proposal aims to do so among high-risk youth (based on maternal psychopathology) during middle childhood (ages 7-9; 50% female), a critical time for interpersonal development. This study measures the interpersonal features of BPD in the context of child-friend interactions to leverage multi-modal assessment and to focus on a central relationship of this developmental phase. Specific aims of the study are to 1) Test whether offspring of mothers with BPD (n=60) exhibit interpersonal features of BPD during middle childhood compared to offspring of mothers with depression (n=60) and non-disordered mothers (n=40); 2) Determine the extent to which BPD interpersonal features in middle childhood impede the development of friendship; and 3) Test associations between BPD interpersonal features and development of psychopathology in children. Friendship stability and quality and child psychopathology (internalizing, externalizing, BPD features) will be assessed at baseline and 6-months. The central hypothesis is that relative to controls, offspring of mothers with BPD are at highest risk of exhibiting interpersonal dysfunction that is specific to BPD during middle childhood. These behaviors have a negative effect on a central developmental milestone of middle childhood: fostering of closeness in friendship, which increases risk a range of psychopathology including BPD. The candidate, Dr. Vanwoerden, is a clinical psychologist seeking to transition to an independent research program focused on the early identification and prevention of BPD. This project is a first step toward this goal with a comprehensive training plan addressing the research questions while building on previous experiences in important ways. First, she will obtain training on the inclusion and assessment of children and friends in research. Second, she will focus on (dyadic) measurement and interpretation of electrodermal activity as a physiological marker of hypersensitivity. Third, she will gain proficiency in longitudinal research design, including retention of high-risk families and the analysis of data using methods aligned with dynamic systems theory. Drs. Stephanie Stepp, Amanda Rose, and Lauren Bylsma who have expertise in the developmental psychopathology of BPD, friendship processes, and psychophysiol...