I was curious in sibling marriages because i noticed that some Egyptians (last time) practised them. There was an article about an emperor (?) of Egypt (?) who was carefully perserved until this day and it stated at his parents were siblings. And he suffered from a cliff lip (?) and died from diseases .... Not too sure but i think it came out around last week for so.
Anyway, here's one website. Will be finding out more!
Incest/Inbreeding Taboos - Sibling Marriage And Human Isolates