Dupuytren's Contracture can be inherited through Viking ancestry or an alcoholic parent.
Get details on Google. 15% of the population on the British Isles have Viking ancestry and the condition has been passed down to various other populations. For example I have 2 friends living in Canada (one of Irish descent the other of German-Scottish ancestry) who both have it.

I also have Dupuytren's Contracture on one hand, four Manx grandparents and no alcoholic parent. Since the Isle of Man was a Viking Kingdom for two hundred years, it would not be unreasonable to assume some Viking ancestry for most people of Manx origin. Dupuytren's Contracture seems to be a good indicator of the Viking presence.