According to University of Washington psychologist Dr. Marsha Linehan, who is one of the world’s leading experts on borderline personality disorder, it results from an emotionally vulnerable child growing up in a particular set of circumstances that she terms an invalidating environment. By an emotionally vulnerable child Linehan means a child whose autonomic nervous system reacts strongly to even low levels of stress and who takes longer than expected to return to baseline, so the child stays emotionally aroused. Linehan believes that this is a biological predisposition that can arise either from genetic factors or from events occurring in the womb before birth or both. It results in what could be called a sensitive nervous system. The interaction between this biological vulnerability and an invalidating environment produces the symptoms of borderline personality disorder.