Relatives of people with borderline personality disorder (BPD) often display certain traits associated with the condition, implying that the disorder could be at least partially hereditary. In a series of studies, researchers from the University of Toronto have illustrated that close relatives of those diagnosed with BPD even exhibit similar brain activity patterns, providing clues as to how the condition might affect entire families.

Characterized by a varied range of clinical presentations, BPD is associated with symptoms including emotional dysregulation, impulsive risk-taking, an unstable and rapidly changing self-image. It is thought to arise from an interaction between various genetic, neurodevelopmental, and psychological factors.

To determine whether or not the condition runs in families, the researchers performed a series of tests on 103 people with BPD, plus 73 immediate family members of people with BPD and 99 individuals with no family history of psychiatric illness.

The first of these studies, published in 2018, revealed that those with BPD and their relatives both have higher rates of depression, addiction, post-traumatic stress disorder, and anxiety than those with no connection to the condition. Certain personality traits such as neuroticism and conscientiousness were also higher in people with BPD and their family members than in the control group.

Following up on these findings, the same researchers sought to understand why families in which at least one member has the condition tend to be particularly prone to arguments. When presented with a series of pictures of faces displaying a range of different emotions, people with BPD and their relatives were both slower than controls at identifying sad faces and were more likely to interpret them as fearful.

According to study author Anthony C. Ruocco, this tendency to misinterpret other people’s emotions “could suggest a heightened sensitivity to signals of threat in families with BPD, which could lead to arguments between family members.”

In December 2021, the researchers published a third study that sought to determine if relatives of people with BPD also display impaired impulse control. According to Ruocco, impulsivity is “potentially the most dangerous symptom of BPD,” and underlies a range of behaviors such as substance abuse and dangerous driving.

When measuring activity in participants’ prefrontal cortices (PFC) as they engaged in an impulse control task, the researchers noted that those with the condition tended to show less PFC activity than controls. Interestingly, though, their relatives typically displayed higher levels of activity.

In their study, the authors speculate that this increased PFC activation may represent a “neurophysiological compensatory mechanism,” implying that relatives of people with BPD allocate more energy to keeping their impulses in check.

Finally, a new study from the same group provides some insight into how these traits combine to influence the complex cognitive processes collectively referred to as executive functions. Using a series of tasks to assess aspects such as attentional vigilance, working memory, and cognitive flexibility, the authors found that those with BPD displayed impaired interference resolution and response inhibition than both their relatives and controls.

Meanwhile, those with the condition and their family members both exhibited “less efficient problem solving and difficulty manipulating mental information.” In spite of these problem-solving deficiencies, however, family members tended to have “stronger response inhibition and abstraction abilities,” which the authors say may provide some “resilience to psychiatric morbidity.”

Summing up the totality of these findings, Ruocco explains that this series of studies is the first to illustrate “how factors in addition to symptoms and personality traits might run in families with BPD.”

“As we better understand these familial factors, we can start to integrate these findings into the treatments for families with BPD.”