Jean, dyscalculus is just as common as dyslexia. I work with special needs children in a mainstream school, and it always amazes me how talented children with either of the above are in other areas.
I'm quite severely dyslexic, but the term didn't exist when I went to school, so I just got the label 'can't be bothered', 'is a lazy writer', etc., and had to find my own strategies to cope with it. Because there was no awareness of dyslexia, nobody stopped me, and I became a linguist with a double degree in languages and literature.