An interesting article regarding NPD.

Narcissistic Personality Disorder: While grandiosity is the diagnostic hallmark of pathological narcissism, there is research evidence that pathological narcissism occurs in two forms, (a) a grandiose state of mind in young adults that can be corrected by life experiences, and (b) the stable disorder described in DSM-IV, which is defined less by grandiosity than by severely disturbed interpersonal relations. The preferred theory seems to be that narcissism is caused by very early affective deprivation, yet the clinical material tends to describe narcissists as unwilling rather than unable, thus treating narcissistic behaviors as volitional — that is, narcissism is termed a personality disorder, but it tends to be discussed as a character disorder. This distinction is important to prognosis and treatment possibilities. If NPD is caused by infantile damage and consequent developmental short-circuits, it probably represents an irremediable condition. On the other hand, if narcissism is a behavior pattern that’s learned, then there is some hope, however tenuous, that it’s a behavior pattern that can be unlearned. The clinical literature on NPD is highly theoretical, abstract, and general, with sparse case material, suggesting that clinical writers have little experience with narcissism in the flesh. There are several reasons for this to be so:– The incidence of NPD is estimated at 1% in the general population, though I haven’t been able to discover the basis of this estimate.

Source: Narcissistic Personality Disorder (NPD) : DSM-IV Diagnostic Criteria