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No one knows exactly what causes BPD, but the familiar nature-nurture combination of genetic and environmental misfortune is the likely culprit. Linehan has found that some borderline individuals come from homes where they were abused, some from stifling families in which children were told to go to their room if they had to cry, and some from normal families that buckled under the stress of an economic or health-care crisis and failed to provide kids with adequate validation and emotional coaching. "The child does not learn how to understand, label, regulate or tolerate emotional responses, and instead learns to oscillate between emotional inhibition and extreme emotional lability," Linehan and her colleagues write in a paper to be published in a leading journal, Psychological Bulletin.
Those with borderline disorder usually appear as criminals in the media. In the past decade, hundreds of stories in major newspapers have recounted violent crimes committed by those said to have the disorder. A typical example from last year was the lurid tale of an Ontario man labeled borderline who used a screwdriver to gouge out his wife's right eye. (She lived; he got 14 years."
There are several theories about why the number of borderline diagnoses may be rising. A parsimonious explanation is that because of advances in treating common mood problems like short-term depression, more health-care resources are available to identify difficult disorders like BPD. Another explanation is hopeful: BPD treatment has improved dramatically in the past few years. Until recently, a diagnosis of borderline personality disorder was seen as a "death sentence," as Dr. Kenneth Silk of the University of Michigan wrote in the April 2008 issue of the American Journal of Psychiatry. Clinicians often avoided naming the illness and instead told patients they had a less stigmatizing disorder.
Therapeutic advances have changed the landscape. Since 1991, as Dr. Joel Paris points out in his 2008 book, Treatment of Borderline Personality Disorder, researchers have conducted at least 17 randomized trials of various psychotherapies for borderline illness, and most have shown encouraging results. According to a big Harvard project called the McLean Study of Adult Development, 88% of those who received a diagnosis of BPD no longer meet the criteria for the disorder a decade after starting treatment. Most show some improvement within a year.