There a several competing theories as to the cause of Narcissistic Personality Disorder. In truth, they may well be complementary.
The prevalent theory is that something traumatic happened in early childhood – somewhere between the ages of 0 and 5. This might be sexual assault, for example. Deeply ashamed, the victim buries this event deep in the psyche and their emotions with it. Their emotional development is arrested in time – which is why many adult narcopaths display such childish emotions from time to time. Rather than their emotions continuing to evolve and mature throughout early childhood, through adolescence and into adulthood, the narcopath will instead study intently and then re-enact the emotional displays of others. In essence their life becomes one complete charade as a “false self” develops to mask from the outside world a deeply troubled, self-loathing “real self”. Amazingly they can’t feel love, empathy, remorse, compassion etc. They just mimic others. It is for this reason that the more intuitive bystander will sense something rather fake about the narcopath.
Studies have shown that the brains of narcopaths do indeed differ from those of normal people – specifically they appear to have unusually thin cerebral cortex when compared to normal people. It is this is the part of the brain that controls what we regard as core human characteristic, or emotional regulators, such as self-awareness, self-determination and self-control. In turn, a smaller part of this cerebral cortex acts as the seat for empathy.
The causality of these differences is less clear. Is it genetic – or is it because that this is the way the brain develops following the childhood trauma? My personal opinion is the latter.
Further reading on the brain studies can be found at this article.
The third large contributory factor is believed to be upbringing, with a very permissive style of parenting that lack consistent boundaries result in children becoming very self-entitled. My own view of this is that such a parenting style may produce self-entitled jerks with high levels of narcissism, but I fear that it is too much of a leap of faith to conclude that this leads to children developing NPD. People with NPD actually have painfully low levels of narcissism and their apparent confidence is merely the charade of the “false self”.
With so little hard evidence to support definitively one theory or another, I rather suspect that NPD is not genetic or indeed hereditary – but it can indeed be passed down from generation to generation. How can this be, if it’s not by genetics? Well quite simply if a parent has NPD, there is a good chance that he/she is going to rear children who in turn struggle with the right emotional development, who in turn aren’t going to make great parents for the next generation. Could they be so abusive as to abuse, or the allow the abuse, of their infant children? I fear so.