What genes can tell us about borderline personality disorder

Borderline personality disorder is often explained through what can be observed: emotions that are difficult to manage, a shifting sense of self, fear of abandonment, impulsivity, or relationships that move from intense closeness to strong rejection. However, behind these experiences, some of which may appear occasionally in many people without indicating the presence of the disorder, lies a more complex question: why do some people develop this condition while others do not? Research published in Nature Genetics now offers the first sufficiently robust genetic clues to begin answering it, although its findings are far from reducing BPD to a purely hereditary condition.

BPD is a mental health condition that particularly affects emotional regulation, self-perception, and the way a person relates to others. It can cause intense mood changes, sensitivity to rejection, persistent feelings of emptiness, or difficulty controlling certain impulsive behaviours. The combination and intensity of symptoms can vary considerably, and the condition should not be confused with bipolar disorder: the latter involves episodes of mania or hypomania, whereas emotional instability in BPD may react more quickly to events in relationships or the surrounding environment.

Its development involves personal, social, environmental, and biological factors. Experiencing trauma, abandonment, abuse, or unstable relationships may increase the risk, but none of these experiences inevitably leads to a diagnosis, as the condition can also appear in people who do not identify such events in their past. Genetics was already considered part of the explanation, but until now, studies had not included samples large enough to determine precisely which variations might be linked to this vulnerability.

The new study gathered data from 12,339 people diagnosed with BPD and 1,041,717 people used as a comparison group, all of European ancestry. The previous genomic study had included only 998 cases and had not identified variants with sufficient statistical strength. By expanding the sample and combining clinical data with biobank information, the researchers were able to examine more than six million genetic markers and identify 11 regions of the genome associated with the disorder.

To understand the result, it is worth looking at the method. A genome-wide association study, known as a GWAS, does not search for a mutation shared by everyone with a particular condition. Instead, it compares millions of small variations distributed across the DNA and checks whether any of them appear more frequently among people with the diagnosis. It would be similar to comparing millions of books belonging to two categories and identifying small changes that occur slightly more often in one than in the other. This association does not prove that a particular variant causes BPD, but it points to regions that deserve closer investigation.

Within or close to those regions, the analysis highlighted several genes that may be involved. Some participate in processes related to the nervous system, cellular communication, or early brain development. Even so, researchers have not discovered “the BPD gene”. The condition is polygenic, meaning that predisposition depends on the combined effect of numerous common variants, each with a very small influence. Having one of them cannot predict a diagnosis, and even carrying many does not mean that the disorder will necessarily develop.

Studies involving families and twins had already suggested that genetics plays an important role in predisposition to BPD. However, this does not mean that a person necessarily inherits the disorder or that it is possible to calculate what percentage of an individual case comes from their genes. Heredity may increase vulnerability, but it does not determine on its own whether BPD will develop.

In this study, the common genetic variants identified explained around 17% of that predisposition. The remainder should not automatically be attributed to the environment: it also includes genetic influences that the study was unable to detect and other factors related to development, personal experiences, and each person’s circumstances.

Another important finding was the overlap with other conditions. The genetic risk associated with BPD showed its strongest correlations with post-traumatic stress disorder, depression, ADHD, and anxiety, as well as links with self-harm, suicidal thoughts, and loneliness. This does not mean that these diagnoses are different versions of the same problem. It suggests that they may share part of their biological architecture, in the same way that two different buildings may use some of the same materials without having the same structure.

This overlap helps explain why diagnosis can be complex. BPD may coexist with depression, anxiety, post-traumatic stress disorder, substance use, or bipolar disorder, and some symptoms can resemble one another. Impulsive behaviour or an intense emotional change is not enough to identify it. Clinicians must consider duration, context, the full combination of symptoms, and their effect on everyday life. Genetic data cannot replace this clinical assessment, and there is currently no DNA test capable of confirming or ruling out the condition.

The study also found links between genetic predisposition to BPD and physical health conditions such as obesity, type 2 diabetes, hypertension, and chronic obstructive pulmonary disease. These are preliminary associations and do not show that one condition causes another. Their value lies in opening a new line of research into the relationship between mental and physical health and examining how much of that connection may arise from shared biological factors, the environment, or lifestyle.

The limitations are clear. The sample consisted of participants of European ancestry, so the findings should not automatically be applied to every population. In addition, some diagnoses came from medical records or healthcare registries, which may use less consistent criteria than an assessment designed specifically for research. Furthermore, identifying a genetic region is only the beginning: researchers still need to determine which mechanisms are involved, when they become relevant, and how they interact.

For now, the finding does not change diagnosis or provide a new medication. Psychotherapy remains the main treatment and can help reduce symptoms, improve daily functioning, and support more stable relationships. The importance of the study lies elsewhere: it provides the first broad genetic foundation for researching BPD, a field that had lagged behind other psychiatric conditions. It also helps challenge a damaging idea: BPD is not a choice, a lack of willpower, or a “difficult” personality, but a complex mental health condition shaped by multiple factors.