Actually, Hops and Guest - to me, it's more than a possibility or theory. It is the central issue about my mom; her issue, her brain - that renders her incredibly difficult for me to deal with. The only reality for her is the one in her own mind... and if other perspectives, viewpoints or opinions or even feelings don't exist there - then, they are "stupid" or bad or wrong.
Could be... maybe... this type of neuro-handicap is behind most N. But how it's manifested and developed from there is probably infinitely variable; individualized, so that it's possible to have the same "root cause" for both a classic N who thinks they're the greatest person in the world and can do/be no wrong (despite evidence to the contrary) and also the Martyr/Saint variation... who will insist with their dying breath how much they've sacrificed; what a poor, pitiful victim they are, despite how many people they hurt to prove that.
In my mother, I've seen that it's almost a learning disability - because the part of the brain that could "imagine" themselves in someone else's shoes - the empathy factor - is also the part of the brain that would allow a person to "imagine" what-if scenarios... and be able to learn from experience and accept a new fact's or tentative set of criteria's impact on her "reality". It is somehow fatally dangerous to her whole reality's structure to allow new stuff in... or admit she was wrong. Like she would fall completely apart into disparate pieces and never be "put back together again"... if she admitted a mistake... or that someone else has their own reality.... with different thoughts, feelings, experiences and opinions.
Like Dr G, I think there is a genetic factor in all this but no one's really figured that one out yet. I can't prove a thing... but I have been haunted by weird similarities between my mom and brother's (and one of my daughter's) way of interacting with everything outside of them. It's as if they've all suffered a stroke in the exact same region of the brain... and while there's some variation in the types of functions available at any given time, and it even sort of has a "cycle" to it... isn't completely all-encompassing and sometimes seems to almost lift and be in the "normal" range... and then wham! they're right back to the reality they call "home" that isn't connected with the rest of the world at all. My mother is the kind who will fight and argue and deny that the sky is "blue", OK? She can't see it; it doesn't exist; I'm wrong... and it hurts her that I'm so messed up... so it's all my fault.
RIIIIIIIIIGGGGGHHHHHHTT.
Neuroscience/neuropsychiatry might provide the only hope for an effective N-therapy... for N's.