I can attest to these things usually being passed down via the maternal lineage. In my family's case though, somehow it jumped to the male side, and when it did it was corrupted - badly. Three generations later, and voila, you have me. Also, apparently there is supposed to be a self-correction mechanism. All of the males in my family who have inherited it since then go slowly psychotic. I beat that, I think, by progressing further with the power and abilities, and training much harder than any previous male. So perhaps I'm safe, perhaps not. Perhaps it is because of the vampirism... who knows.