Etiology of BPD
Like other major psychiatric disorders, the etiology of the borderline personality disorder (BPD) involves both genes and environment. The genetic component, which has been underappreciated, is substantial. It is not, however, the disorder itself which is inherited. Rather, what is inherited are forms of temperament that predispose a child to develop this disorder. The predisposing temperaments (aka phenotypes) for BPD are Affective Instability, Impulsivity, and Needy/Fearful Relationships.
Each of these temperaments predisposes to other disorders as well as BPD; Affective Instability also predisposes to mood disorders, Impulsivity also predisposes to substance / alcohol abuse, bulimia, and conduct disorder, and Needy/Fearful Relationships also predispose to histrionic, dependent, and avoidant personality disorders. The presence of these inherited temperaments helps explain why patients with BPD are often co-morbid with these other disorders.
Still, these predisposing temperaments do not by themselves explain the etiology of BPD. They make it possible for someone to develop this disorder. To develop BPD also requires unfortunate environmental conditions. Most theories believe that early caretaking experiences are very important. Here, patients who have BPD will often report that their parenting was inconsistent, neglectful, or even malevolent.
This perspective is deeply distressing to parents. Some parents will feel deeply guilty as they review the past and elaborate on their failures. Others will dismiss the accusations, deny having any role, and thereby add to their borderline offspring’s alienation.
Early caretaking relationships are significantly shaped by the child. This contrasts with the more widely recognized belief that parental interactions significantly shape the child. Thus, the easily upset, needy/fearful, hyperactive child who possesses the predisposing temperaments for BPD will pose special problems for parents. Such a child will benefit from forms of parenting that may not come natural to their parents.
The easily upset child may need an unusually calm and patient caretaker. In its absence their emotions may be poorly integrated and disturbing to them. The needy/fearful child may require a consistently involved reassuring caretaker. In its absence, their fears of abandonment may become unrealistic. An impulsive child may need parenting marked by predictability and non-punitive limit setting. In its absence, they may not develop self-controls.
Regardless of the early childcare, the child with predisposing temperaments for BPD will be far more easily undone by traumatic events. Most children with trauma grow up without sequelae. Those who suffer enduring consequences from trauma have both a predisposing temperament and — perhaps due to problematic early caretaking — will often have failed to disclose and process the event with their caretakers.
It is not easy to develop BPD. I expect that only a small fraction of the people who have the genetic disposition go on to develop it. Parenting is sometimes dysfunctional, but villains are truly rare. We need far more research to understand the contributions of both genes and environment.