Causes of Borderline Personality Disorder

Borderline personality disorder (BPD) is a Cluster B personality disorder in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). According to the American Psychiatric Association, Cluster B disorders are characterized by behavior that is dramatic, erratic and emotional.

Unfortunately for the community of people who have borderline personality, there is little consensus on the cause of the disorder. Approximately 1.8 percent of people in the United States are affected by this disorder. The societal implications are even greater, as borderline personality uses community mental health resources the most of all psychiatric disorders.

Researchers do know from twin studies that genetics plays a role in personality disorders. Environmental factors, such as childhood abuse, neglect and separation from caregivers, as well as brain abnormalities, emotion regulation, impulsivity, aggression and serotonin levels all play a role.

Despite the wealth of research on the subject, there is much disagreement on the causes of BPD. Some researchers have found that individuals with borderline personality disorder were more likely to have a history of childhood trauma including physical abuse or sexual abuse. Other researchers assert that those with the disorder or borderline traits may have been witnesses to domestic violence as children.

Understandably, the relationship between child sexual abuse and borderline personality disorder has been a prominent issue. Some researchers estimate that 30 percent of female survivors of childhood sexual abuse will develop borderline personality disorder. Alternately, some researchers suggest that a range of 60 to 90 percent of women with borderline personality disorder have been victims of childhood sexual abuse.

It is important to note that not everyone with a history of childhood sexual abuse will develop the disorder. Researchers point out that most individuals who experience childhood adversity do not develop personality disorders in their lifetime, so examining the relationship between mediators and moderators in this association is important. One protective factor for later development of psychopathology is social support.

Other variables, such as genetic make-up, can buffer environmental adversity. Because many personality domains are heritable, borderline personality disorder may be a result of a genotype interacting with adverse environmental factors. This would in turn lead to the expression of borderline symptoms or other dysfunctional personality traits.

Researchers have found that personality disorders develop from a combination of genes and environmental effects on personality traits. For example, variants of the serotonin transporter gene have been linked with an increased risk for affective disorders. In addition, many people with BPD suffer from co-morbid diagnoses of major depression, anxiety disorders, obsessive compulsive disorder, substance abuse or other personality disorders.

This is in line with the serotonin transporter gene research, as it has been connected to emotional and social human behavior. For example, the presence of one or two copies of the short (s) allele of the 5-HTTLPR polymorphism is related to increased fear and anxiety behaviors. Carriers of this s allele, in particular those with two, are at an increased risk for depressive symptoms if exposed to stress. This ss genotype has also been associated with OCD and suicidal behavior.

So far, researchers have found that BPD runs in families and occurs more frequently in biological than adoptive relatives. There are also significantly more incidences of BPD in identical twins than fraternal. Impulsive aggression and emotional instability in particular may be influenced by genetics. Neuropsychologists reason that there are several pathways to developing BPD, related to both environmental and biological factors. This school of thought holds that an increased risk for BPD may be related to deficits in mentalization (little or no attention to internal mental states) and the inhibition of mentalizing due to abuse or neglect during childhood.

A developmental, bio-behavioral switch model of the connection between mentalization, stress and attachment in BPD may be able to explain the hypersensitivity and the low threshold for attachment system activation. The interaction between the developmental, biological and psychosocial factors in this disorder increases susceptibility to contagion from others’ mental states and dysfunction in the stress-regulation system. In other words, people with BPD have a low threshold for activation of the attachment system when under stress.