I should think that the most obvious cause of physical disorders and early deaths would have been the custom of royal incest among the pharoahs. Inbreeding usually causes health problems after a while.
That’s a separate issue from the idea that it would take some sort of illness to bring on the concept of monotheism. Perhaps the scientists who posit this are themselves suffering from some sort of mental disorder.
Inbreeding also can lead to stunning intellects; but Julius Caesar had epilepsy, and he was a) inbred and brilliant, but b) didn’t have mystic visions. :’)