Despite protestations in some quarters that it’s just a brain disorder
and that’s all, almost all studies of subjects of borderline personality
disorder (BPD) show a significant percentage of them were found to have a
history of child abuse, including physical, sexual, and psychological. Since
research subjects may not all be truthful about matters like that, the
percentage is probably higher than those reported. Frank abuse is of not seen in
all cases, of course.
In getting to the bottom of the family dynamics of my psychotherapy patients
over the last 40 year, 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 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 DBT – the predominant psychotherapy
paradigm for the disorder – is an almost universal feature of BPD families.
A good meta-analysis (studies that combine the
results of several study 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. in Acta
Psychiatrica Scandinavia (2019).
A
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., Journal of Psychopathology and Clinical Science, (2019). But
it has some of the same logical flaws I’ve documented in a previous post.
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 here 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 is
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 that its
data in all likelihood also underestimates the prevalence of adverse childhood
experiences, thereby minimizing any differences in the way each twin was
treated.