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Genetics plays a larger role in the development of BPD than previously thought.

The brains of people diagnosed with BPD are significantly different from normal brains.

Moderate to high functioning people with BPD rarely get diagnosed or included in research studies.

We do not yet know whether higher functioning people with BPD have an equally high genetic component.

I have been treating clients for borderline personality disorder for more than 45 years. When I first started studying the topic, most theorists emphasized the role early abandonment trauma played in its development. A great deal of research focused on 14 to 24 months as a critical window when normal personality development could be derailed, and borderline personality disorder could develop instead (Mahler, Pine, and Bergman, 1975).

However, that never seemed like the whole answer, as there were so many clients with different histories who developed borderline adaptations.

I am using the terms borderline adaptations and BPD as shorthand for someone who qualifies for a full diagnosis of borderline personality disorder.

The Genetic Component of BPD

Today, advances in neuroscience suggest that there is likely to be a much stronger genetic component involved than most theorists previously believed. Unfortunately, most current research on the genetic origins of BPD includes only people who are low-functioning. Most moderate-to-high-functioning people with BPD never get diagnosed or included in research studies.

Estimates Are Likely to Be Too High

Because most estimates of the genetic component of BPD are taken from brain scans or studies of the lowest-functioning group, they are unlikely to represent all people with BPD. We will not be able to get more accurate and inclusive data until we can study the brains and genetic history of the moderate- to high-functioning people with BPD who do well in individual psychotherapy and never need hospitalization or any form of emergency care.

35% Concordance Rate in Monozygotic Twins

Monozygotic twins are often called “identical twins” because they have identical genetic profiles. If only genetics mattered, we would expect both twins to develop BPD 100 percent of the time if one twin did so. However, the concordance rate for BPD is estimated to be about 35%, compared to an average in the general population based on pooled estimates of around 2.4%. (Torgersen, S. et al, 2000). Heritability estimates of BPD are about 46% (Kendler, K. S. et al, 2019).

Even if the number drops considerably when higher-functioning people with BPD are included, the data still suggests that theorists have probably been underestimating how much family genetics plays a role in who develops BPD.

Neurological Findings about the Borderline Brain

Brain scans of adults with BPD that made it into research studies show there are some significant differences from normal brains (Driessen et al, 2000):

16.0% smaller hippocampus (involved in memory and spatial relations)

7.5% smaller amygdala (our emotional STOP sign intended to keep us safe).

Reduced activity in the prefrontal cortex (involved in reasoning, analysis, and planning).

We do not yet know whether the differences were present at birth or acquired during childhood. We do know that the brain is plastic, changing in response to input, and not formed once and for all by adulthood. We also know that most cases of BPD respond well to appropriate psychotherapy, and we currently have multiple approaches to BPD that work for many people:

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Dialectical behavior therapy (DBT)

James F. Masterson’s developmental, self, and object relations treatment

Otto Kernberg’s object relations treatment

Various combination approaches, such as my Masterson-informed gestalt therapy or schema therapy, which has its roots in cognitive behavior therapy (CBT).

Because these methods have worked to diminish or even eliminate borderline personality disorders in motivated clients, we know that even the brains of people genetically predisposed to BPD can be positively impacted by appropriate psychotherapy.

Neuroscience and Psychotherapy Interventions

The good news about finding out where the significant differences are between borderline brains and normal brains is that we can now theoretically design interventions that specifically target the overactive and underactive areas of each client's brain. Neuroscience data is transforming the field of psychology and directly impacting psychotherapy methods.

James F. Masterson on the Causes of BPD

I am fortunate that I received my training in BPD from James F. Masterson (1926-2010), the author and editor of numerous books on the diagnosis and treatment of BPD. Masterson was ahead of his time by acknowledging that there were other ways to develop BPD besides bad parenting (1976, 1981).

He taught that three factors could combine in different ways to contribute to the development of BPD:

Nature—genetics and inborn temperament

Fate—unplanned events (wars, maternal illness, and more)

Wisely, he also insisted that we read and understand the work of child development experts who studied the other factors that could contribute to developing BPD. I will briefly summarize a few of the other viewpoints we were taught to consider.

A Mismatch Between the Child’s Needs and What Parents Could Supply

Stella Chess and Alexander Thomas, child development experts who wrote extensively about the impact of the child’s inborn temperament on parenting, described three basic types of infant temperaments—easy, slow to warm up, and difficult—and nine different temperamental variables that affect how children adapt during childhood: activity level, rhythmicity/regularity of biological functions, distractibility, adaptability, approach/withdrawal, attention span and persistence, intensity of reaction, threshold of responsiveness, and mood (Chess, S. and A. Thomas, 1984).

They concluded that a bad mismatch between what the child needs and what the parents provide could interfere with the child’s healthy development enough to create future problems, even if there was no mistreatment.

Fate in the Form of Unexpected Events

By “fate,” Masterson meant all the things that go wrong for the child that could not be avoided by the parents. This includes such unanticipated abandonment trauma as:

Young children of immigrants are being separated from their parents.

A mother is becoming ill and has to be hospitalized for a long time.

The parents have more children than they can take care of properly.

Bad Timing—The Terrible Twos

Mahler, Pine, and Bergman (1975), authors of The Psychological Birth of the Human Infant, believed that the time period from 14 to 24 months (informally known as “the terrible twos”) was critical for the development of BPD. Children in this age group may rapidly shift from demanding independence, saying “no” to everything, and having a public tantrum to wanting to be held, comforted, and reassured that they are loved.

Most parents find this stage difficult. It is easy to mismanage adapting to the child’s rapidly changing needs—especially if you have a child that Chess and Thomas might consider more difficult to parent, or are distracted by other important issues such as moving to a new country or an unexpected illness.

Mahler and her group tested their hypotheses by setting up a free clinic for mothers with a child in this age group who agreed to be filmed for later study during interactions with their child. Their results appeared to confirm their hypothesis that parenting difficulties during this critical period contributed to the later development of BPD.

There appears to be more than one way to end up with a borderline personality disorder. Some combination of three factors—genetics and temperament, parenting, and unexpected abandonment trauma at around age two—can combine in a variety of ways to manifest BPD in a vulnerable young child. Neuroscience-informed research on the origins of BPD is likely to give us more precise information in the future.

Masterson, J. F. (1976). Psychotherapy of the borderline adult. NY: Brunner/Mazel.

Masterson, J. F. (1981) The narcissistic and borderline disorders (1981),

Mahler, M., Pine, F, & Bergman, A. (1975). The psychological birth of the human infant. NY: Basic Books.

Chess, S., & Thomas, A. (1984). Origins and evolution of behavior disorders. NY: Brunner/Mazel.

Driessen, M., Herrmann, J., Stahl, K., Zwaan, M., Meier, S., Hill, A., Osterheider, M., & Petersen, D. (2000). Magnetic resonance imaging volumes of the hippocampus and the amygdala in women with borderline personality disorder and early traumatization. Archives of General Psychiatry, 57 (12), 1115-1122.

Kendler, K. S., Aggen, S. H., Czajkowski, N., Roysamb, E., Tambs, K., Torgersen, S., Neale, M. C., & skoglund, C. (2019). Familial risk and heritability of diagnosed borderline personality disorder: A total population study of 1,851,755 Swedish residents. Molecular Psychiatry, 24 (5), 742-750.

Torgeren, S., Lygren, S., Oien, P. A., Skre, I., Onstad, S., Edvardsen, J., Tambs., & Kringlen, E. (2000). A twin study of personality disorders. Comprehensive Psychiatry, 41 (6), 416-425.

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