Borderline personality disorder and the new insights into its neurobiology
Research is making its first promising steps toward understanding the disorder and tailoring treatments for affected individuals.

*Names have been changed to protect anonymity 

Theo* never liked himself. He changed his hairstyle countless times, hid himself in larger clothes, and never trusted his social skills. Anger often followed his laughter in less than a minute, creating intense conflict with his peers. These brutal mood swings ended most of his relationships. For years, Theo thought that he wasn’t normal, that something was wrong with him. He isolated himself from those closest to him, including him mom, Natalie*. That was until he was diagnosed with borderline personality disorder in October 2021. 

Borderline personality disorder (BPD) isn’t as commonly known as other mental disorders such as schizophrenia or bipolar disorder. Affected individuals often experience an altered self-perception, intense fear of loneliness, and extreme impulsiveness. These severe symptoms piqued the interest of Anthony C. Ruocco, professor, interim chair, and director of clinical training in the Department of Psychological Clinical Science at the University of Toronto Scarborough. 

“When I was an undergraduate student, I worked with a professor who studied personality disorders, and I became passionate about BPD because it was a disorder that was seen as quite severe—yet we didn’t know very much about its neurobiological origins,” says Professor Ruocco. “People with BPD are sometimes suicidal, many have some difficulties knowing who they are, experience significant interpersonal problems, and some people can be very impulsive.”

BPD affects around 1.6 per cent of the general population. Many individuals with this disorder struggle to keep a job or complete their education, exhibit reckless behaviours such as fast-driving or alcohol abuse, and face a higher risk to fall into depression, engage in self-harm, or attempt suicide. 

In the past, individuals with BPD were often stigmatized as being resistant to treatment due to a lack of understanding of the disorder, which sometimes led to misdiagnoses. However, over the last few years, awareness has grown significantly, as certain celebrities have shared their condition publicly. For instance, Pete Davidson, an American comedian known for his Saturday Night Live sketches, opened up about his diagnosis back in 2017. “I was always just so confused all the time, and just thought something was wrong,” said Davidson in an interview. “When somebody finally tells you, the weight of the world feels lifted off your shoulders.”

Awareness about BPD is the first step toward accessing specialized treatments for the disorder. However, research still has a long way to go to determine its neurobiological and genetic causes, which can ultimately create individual-specific treatments to improve the management of this disorder. One of the ways by which research has advanced in this field is through family studies. 

Family studies normally examine people with BPD, along with their immediate biological relatives, to contrast behaviours and examine relationships and interactions. Professor Ruocco’s research pioneers the use of family studies to examine the neurobiology and other related characteristics of the disorder. His two most recent papers, published in March and November of last year, examined potential so-called “intermediate phenotypes,” an essential first step to better understand BPD. So, what are intermediate phenotypes and how can they accelerate research? 

Intermediate phenotypes bridge together genetic sources with observable symptoms of the disorder such as impulsivity. There are smaller manifestations of the disorder that usually cannot be observed from the outside. Because they are unique to the disorder and simpler to study, intermediate phenotypes can help identify certain genes that develop BPD. For example, people with diabetes tend to feel very thirsty. Luckily, researchers were able to identify insulin-resistant receptors in people with diabetes that not only explain the thirst symptom, but also act as an intermediate phenotype that clues us into the genetic causes of the disease.

“Understanding genes will better point us in the direction of treatments that will be more beneficial for one person with BPD versus another,” explains Professor Ruocco. His research aims to uncover biological markers specified by intermediate phenotypes—and family studies are essential to reach this goal. Identifying intermediate phenotypes related to BPD would help determine the genes responsible for the disorder. These genes could then be the key to differentiating between various types and severities of the disorder, leading to the development of targeted treatments.

Previous studies have shown that people with BPD are strongly sensitive to facial expressions of emotion. They can interpret neutral facial expressions as fearful and perceive unintended anger or disgust in negative facial expressions. Thus, Professor Ruocco and his team first studied the potential of facial expression interpretation bias as an intermediate phenotype. His team wanted to know if family members of BPD-affected individuals showed the same bias.

Professor Ruocco’s study yielded two main findings: biological relatives do not perceive emotions in neutral facial expressions—this feature seems to be unique to people with the BPD diagnosis itself; and both people with BPD and their biological relatives tended to interpret sad facial expressions as fearful. This bias shared by people with BPD and their relatives may partially explain the prevalence of interpersonal conflicts among families affected by BPD. “We have what some might call a ‘hyper-arousal’ that is not only present in people with BPD, but also potentially in relatives. And it might impact the way that they perceive emotional expressions,” explains Professor Ruocco.

In his most recent paper, Professor Ruocco aimed to uncover biological markers related to one of the most common symptoms of the disorder—impulsiveness. Impulse control arises from executive functions, which reflect self-control and thinking-on-the spot abilities. Using family studies, he employed cognitive tasks assessing such skills as planning and attentional vigilance in people with BPD, along with their first-degree relatives. Professor Ruocco found that most people with BPD showed greater difficulties with executive functions, which directly impacted their ability to achieve goals. 

On the other hand, first-degree biological relatives who didn’t have a mental disorder diagnosis displayed strengths and weaknesses. They showed less efficient problem-solving abilities than controls with no history of mental disorder, but also displayed higher self-control skills. 

Theo’s mom, Natalie, agrees with those findings. “Maintaining my relationship with [him] requires me to show abstraction and resilience in order to control myself and avoid upsetting him,” she shares. 

According to Professor Ruocco, his recent findings are essential, as they may constitute clues that could ultimately unlock insights into the genetic basis of BPD. “We want to understand whether the traits we are studying are indeed intermediate phenotypes and whether they truly reflect some important characteristics that we need to acknowledge and better understand in family members who have someone affected with BPD,” he says.  

In the meantime, support and treatments for people diagnosed with BPD and their families are essential. Some of the most common treatments to date include dialectical behaviour therapy, which emphasizes coping skills that are intended to increase self-control and reduce self-harm. Mentalization-based treatment is another method that targets emotion management and stability towards oneself and others. However, those treatments are not the only options currently available. The Sashbear Foundation is a Canadian fundraiser and awareness campaign that provides support and skills training to increase awareness and inclusion for people struggling with mental illnesses. 

When faced with those opportunities, Natalie is both hopeful and worried. “We would need Theo to accept a familial therapy, and then we also need to find a therapist that he likes, someone who understands him. It’s not easy,” she concludes. “However, we succeeded in building—or re-building—a relationship based on love and trust. It can be very hard, but I’m hoping for the best.”


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