As discussed in "What kind of parenting leads to NPD?" children can have strong reactions to constant perceived criticism.
Boys and girls usually have different ways of dealing with criticism. Girls tend to internalise the criticism they receive whereas boys tend to cast it out. This may be explained by the fact that the female brain functions in a different way to that of a male brain. It could also be due to the manner in which girls are primarily socialised as nurturers who shoulder the burden when things go wrong within the family. This role of the female nurturer is also encouraged through the mass media. For these reasons it is possible that women will more readily give up their narcissism in favour of another persons need and are therefore less likely to develop NPD than a man.
Women who have experienced an unempathic upbringing similar (sometimes more abusive) to that of men who suffer from NPD are more susceptible to developing Borderline Personality Disorder (BPD) as opposed to NPD. They tend to have a poor self-image seeing themselves as "worthless" as opposed to the grandiose image that sufferers of NPD have of themselves.
From an early age, the casting out of criticism on to other sources starts the pattern that leads to denial of faults. The child clings to the idea of themselves as "omnipresent" and "good" and projects these faults on to others who are "weak" or "bad". This behaviour is evident in sufferers of NPD and because boys tend to do this more than girls it may be an explanation as to why more men suffer from NPD than women.
Some Psychologist have also sought to demonstrate that the reason there are more men diagnosed with NPD than women is that the Psychologist making the diagnosis has their own bias and stereotypes of relating to the sexes.
The outlook isn't great. Often age and the degree of the narcissistic disturbance will determine the success of any possible treatment. Those on the lower end of the scale or those who are less resistant to change due to their youth usually benefit from psychotherapy (the most widely adopted treatment for NPD). They can learn to accept their condition and begin to pay attention to their feelings, possibly gaining a better awareness of Self, experiencing a wider range of emotions and empathy for others. The end result is unlikely to be the big "cure" they initially go to therapy for.
The biggest problem facing the healing of a Narcissist is the Narcissist themselves. Firstly, Narcissists would have to admit that something was wrong with them in order to go and seek any form of therapy. Given their grandiose nature this is unlikely unless a traumatic life event such as divorce, loss of job, imprisonment, serious illness etc. takes place. When they enter therapy they may do so only to treat their symptoms not the underlying problem or they may do so to learn how to become "perfect".
Secondly, when they do find the strength to go to therapy they will be looking to extract narcissistic supplies from their Therapist. They will interact in the same way they do with others and begin the cycle of inflation (where the Therapist is respected by the patient) and devaluation of the Therapist (where they are seen as incompetent). The Narcissist will also project/transfer their feelings on to the Therapist who must decipher and deal with it in a manner that ensures the patient doesn't feel that they are being attacked or "bad" to have these feelings.
Thirdly, Narcissists may become disillusioned with their treatment and give up seeing it as a waste of time because "the cure" doesn't happen fast enough. The Therapists work is repetitive in nature as the patient resists their efforts to help them heal, so it may appear to the Narcissist that no progress is being made. Narcissism is difficult to treat and it can take years to make a break thorough (if a break through ever occurs). Not surprising really when you think that the Therapist is in essence trying to re-parent their patient in the hopes of helping them to develop a sense of Self and awareness of others separateness and value.
Fourthly, some Therapist's will give up on the hope of helping the Narcissist too early. In conjunction with the behaviour described above Narcissistic patients can be ungrateful and critical of their Therapist, show anger at not receiving special treatment they feel they are entitled to e.g. not being accommodated for being late to an appointment, the Therapist taking a week off for a holiday or being off sick etc.
In addition some Therapist's may have unresolved narcissistic conflicts of their own which will impede the care they are able to give to their patient. Usually Therapists are supervised or go through analysis themselves in order to ensure that this doesn't happen.
In order for psychotherapy to have any benefit the Therapist must foster a non-judgemental and empathic environment in which treatment can take place. They must be able to read the signals (verbal and non-verbal) given to them by the Narcissist, interpret them and apply appropriate responses in order to facilitate growth and understanding - missing the signals can cause setbacks of varying degrees. Sounds like a difficult job - who'd be a Therapist?