Borderline Symptoms at Age 12 Signal Risk for Poor Outcomes During the Transition to Adulthood: Findings From a Genetically Sensitive Longitudinal Cohort Study

Objective: Borderline personality disorder in adolescence remains a controversial construct. We addressed concerns about the prognostic significance of adolescent borderline pathology by testing whether borderline symptoms at age 12 years predict functioning during the transition to adulthood, at age 18 years, in areas critical to life-course development. Method: We studied members of the Environmental Risk (E-Risk) Longitudinal Twin Study, which tracks the development of a birth cohort of 2,232 British twin children. At age 12, study members' borderline symptoms were measured using mothers' reports. At age 18, study members' personality, psychopathology, functional outcomes, and experiences of victimization were measured using self-reports, coinformant reports, and official records. Results: At age 18, study members who had more borderline symptoms at age 12 were more likely to have difficult personalities, to struggle with poor mental health, to experience poor functional outcomes, and to have become victims of violence. Reports of poor outcomes were corroborated by coinformants and official records. Borderline symptoms in study members at 12 years old predicted poor outcomes over and above other behavioral and emotional problems during adolescence. Twin analyses showed that borderline symptoms in 12-year-olds were influenced by familial risk, particularly genetic risk, which accounted for associations with most poor outcomes at age 18. Conclusion: Borderline symptoms in 12-year-olds signal risk for pervasive poor functioning during the transition to adulthood. This association is driven by genetic influences, suggesting that borderline symptoms and poor outcomes are manifestations of shared genetic risk.