? What is narcissistic personality disorder Personality disorders are one of the ten personality disorders listed in the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association. Recent studies in psychology have shown that personality disorders are strongly linked to both environmental and genetic factors. In general, a personality disorder is defined by the long-term presence of internal experiences and external behaviors that differ significantly from the norms of an individual’s society and culture. These experiences and behaviors are stable across situations, do not change much over time, and cause significant distress to the individual. According to recent research, individuals with personality disorders also often experience increased rates of anxiety and ...