Childhood Trauma in Borderline Personality Disorder

Source: Edna and Alice Nash (Vitagraph Twins); Unknown author/Public domain

Despite protestations in some quarters that it’s "just a brain disorder," almost all studies of people with borderline personality disorder (BPD) show that a significant percentage of them have a history of child abuse, including physical, sexual, and psychological. Since research subjects may not all be truthful about such matters, the percentage is probably higher than those reported.

Frank abuse is, of course, not seen in all cases. In getting to the bottom of the family dynamics of my psychotherapy patients over the last 40 years, I discovered that some of their parents are instead hyper-involved yet resentful helicopter parents who try to protect their children from any and all problems—which invalidates their children's feelings about their ability to take care of anything on their own.

Parents invalidating their kids’ thoughts and feelings, posited as one of the causes of the disorder by Marsha Linehan’s dialectical behavior therapy—the predominant psychotherapy paradigm for the disorder—is an almost universal feature of BPD families.

Research on the connection between BPD and adverse life experiences

A good meta-analysis (a study that combines the results of several studies to add strength to the conclusions of any one study) that corroborates theoretical proposals that exposure to adverse life experiences is associated with BPD is “Childhood adversity and borderline personality disorder: a meta-analysis” by Porter et. al.

A relatively new study, however, seems to show that this is not the case (“Childhood trauma and borderline personality disorder traits: A discordant twin study” by Skaug, et al.). But it has some logical flaws of the type I've documented here previously. It was a study of “discordant” twins (where one is healthier than the other) and was based on their self-report using a structured interview called the Childhood Trauma Interview. Small but statistically significant associations between childhood trauma (CT) and BPD traits were initially found in the total sample.

However, after controlling for “shared environmental” and genetic factors in the discordant twin pairs, the analyses showed little to no evidence for causal effects of CT on BPD traits. The authors concluded that the associations between CT and BPD traits stem from common genetic influences.

The elephant in the room here is the definition of “shared environment.” The assumption is that both twins grew up in the same environment, which further presumes that their parents treated both of them the same. As anyone with a sibling or more than one child knows, this is nonsense. Differences in the way the parents treat the two children might even be exacerbated by the fact that one twin became, over time, "healthier" than the other, which could mean they had different parental responses to them at least some of the time.

If you assume the shared environment is the same with parents treating both kids the same, of course, genetic differences will stand out more. The study also ignores the fact that self-reports about childhood abuse are often dishonest in order to go along with family rules about hiding such things from outsiders, so its data in all likelihood also underestimates the prevalence of adverse childhood experiences, thereby minimizing any differences in the way each twin was treated.