First of all, an IQ measurement is nonsense. One gets varying results, depending on the kind of test, personal preferences and qualities. You can even practice those tests and get better at it. Does this mean you get smarter?
Secondly, you may wonder what disabled people are capable to do! Euler became blind and he still proved mathematical theorems. He only needed someone to write them down.
Furthermore it isn't true, that anyone's IQ (which way ever measured) is fixed. O.k., you cannot make a stupid person a genius, but training, experience and books, a lot of books, can change a lot!
Mathematics isn't something about IQs. It's very much the same as with everything else: practice, patience and diligence. You aren't supposed to be a genius. Curiosity is much more important, and the other attributes I mentioned. Of course not every runner can be a Usain Bolt, every physicist an Albert Einstein or every mathematician a Leonard Euler.
However, there is one important lesson to learn: Do not believe something, just because anyone has said so! The other way around makes you a good scientist: Wrong, until proven! In mathematics, you learn to read those proofs which are to convince you. In physics you do experiments.
What makes you think what you've read is right? It is not. And this has to become your standard assumption: it is wrong unless proven to you.