Although the cause of borderline personality disorder is unknown, both environmental and genetic factors are thought to play a role in predisposing people to BPD symptoms and traits. BPD is approximately five times more common among people with close biological relatives with BPD.

Studies show that many individuals with BPD report a history of abuse, neglect, or separation as young children. Forty to 71 percent of BPD patients report having been sexually abused, usually by a noncaregiver.

Researchers believe that BPD results from a combination of individual vulnerability to environmental stress, neglect, or abuse as young children and a series of events that trigger the onset of the disorder as young adults. Adults with BPD are also considerably more likely to be the victims of violence, including rape and other crimes. These incidents may result from harmful environments as well as the victims’ impulsivity and poor judgment in choosing partners and lifestyles.

Neuroscience is revealing brain mechanisms underlying the impulsivity, mood instability, aggression, anger, and negative emotion seen in BPD. [Insert by A.J. Mahari: These are the claims and yet professionals are still saying this is very early ‘research’ and they cannot prove the findings that are still unproven and thus remain at most theory, and at worst mis-represented information – end A.J’s insert] Studies suggest that people predisposed to impulsive aggression have impaired regulation of the neural circuits that modulate emotion. The brain’s amygdala, a small almond-shaped structure, is an important component of the circuit that regulates negative emotion. In response to signals from other brain centers indicating a perceived threat, it marshals fear and arousal, which may be more pronounced under the influence of stress or drugs like alcohol. Areas in the front of the brain (prefrontal area) act to dampen the activity of this circuit. Recent brain-imaging studies show that individual differences in the ability to activate regions of the prefrontal cerebral cortex thought to be involved in inhibitory activity predict the ability to suppress negative emotion.

Serotonin, norepinephrine, and acetylcholine are among the chemical messengers in these circuits that [A.J Mahari: are thought to not proven beyond doubt to – end insert] play a role in the regulation of emotions, including sadness, anger, anxiety, and irritability. Drugs that enhance brain serotonin function may improve emotional symptoms in BPD. Likewise, mood-stabilizing drugs that are known to enhance the activity of GABA, the brain’s major inhibitory neurotransmitter, may help people who experience BPD-like mood swings. Such brain-based vulnerabilities can be managed with help from behavioral interventions and medications, much as people manage susceptibility to diabetes or high blood pressure.