One of my past boyfriends found out that his mother had huntington's while we were dating, and in fact his mother's funeral was yesterday :-( it was very scary for him to find out that he had a 50-50 chance of dying a slow, horrible death, but I never would have dreamed of breaking up with him over that if i really thought we were meant for each other.
Adoption if nothing else, IMO. He specifically said he didn't want to know if he had the gene and he refused to have kids for fear of passing it on to them.