Although traumatic events in childhood are associated with a greater risk of borderline and other personality disorders, the actual cause of personality disorder isn't known. Most likely, no single factor explains its development. Instead it may be caused by a combination of heredity and environmental factors.      Borderline personality disorder is a serious emotional disturbance that's characterized by disappointing and unstable personal relationships, intense anger, impulsive actions, feelings of emptiness, and fears of abandonment — real or imagined. It may be that emotional trauma at a time when the brain isn't fully developed alters something in the brain, which decreases the ability to effectively deal with stressful situations