To examine the interaction between attachment, emotional dysregulation and mentalising in the development of borderline personality disorder (BPD) traits in child and adolescent populations.

A systematic review was conducted following PRISMA guidelines, integrating nine empirical studies. Developmental trajectories were analysed using a cascade model linking early adversities with dysfunctional clinical outcomes.

The evidence confirms that childhood trauma (emotional abuse and neglect) and insecure attachment in early life establish a primary vulnerability that compromises self-regulation. This deficit, mediated by emerging borderline traits, triggers transdiagnostic emotional dysregulation. The “developmental cascades” model shows how harmful behaviours—both non-suicidal self-injury and aggression towards others—mutually reinforce each other, worsening prognosis. Mentalising and epistemic trust emerge as critical dimensions: impaired reflective functioning predicts externalising behaviours, whereas epistemic ambivalence is associated with severe internalising symptomatology. Paradoxically, in individuals with a high borderline load, greater perceived emotional competence is associated with an increase in self-injury, consolidating it as a dysfunctional regulatory strategy.

The prevention of BPD in children and adolescents requires a multidimensional approach that goes beyond behavioural containment. It is imperative to restore epistemic trust, promote active emotional validation within the family system, and achieve the early cessation of self-injury in order to interrupt pathological feedback loops and safeguard functional long-term outcomes.