I cant remember exactly what daf it was. In Masechte Ksubos it says that if someone marries a woman and then finds out that she is a baal mum he can leave her and he doesnt have to give her a get. I think it is Rashi who says this is only mum that a kohen isnt allowed to have. Does that mean that if you marry a women and then find out that she's a left-hander (a left hander's a Baal Mum) the whole marriage was no good?
The Mishna is found in Kesuvos 72b - Mumim of Kohanim are Mumim for women. See also Shulchan Aruch EH 39:3: If one says, "I marry you on the condition that you have no Mumim, if there is a Mum she is not married."
If no condition was made, if there is a Mum which people are bothered by, the marriage is doubtful (Safek) (39:5). Even so, the Chelkas Mechokek ( 39:9) adds that if when he finds out he does not object, the marriage is definite. So, if someone discovers that his wife is a lefty, since 1) no condition was said, 2) people are not Makpid on lefties, and 3) he would not complain on finding out, there is no problem at all with the Kidushin.
If he did say before the marriage only if she has no Mum there is a problem with the Kidushin (only a Safek exists because he could have meant only Mumim that people care about even though he did not say so openly [Aruch haShulchan 39:14]). But the Chavas Ya'ir (3:20) concerning another case adds that this is only if he said no "Mum." But if he says she should have no Chisaron (lack, missing) the marriage is good without a doubt since lefty is not a lacking at all, only a state which is Halachicly called Mum.
All the best,
Reuven Weiner