Frank:

If your family does indeed have myotonia congenita, then it sounds like you have the dominant form, Thomsen MC. For some reason, it seems to affect the upper body more than the recessive form, Becker MC.

As Jan mention it has nothing to do with the X chromosome (or Y chromosome). That you are the first male to be affected would be merely a matter of chance. For autosomal dominant disorders, such as MC, the chance that the offspring of an affected individual will also be affected is 50%. Additionally for what might be various reasons, Thomsen MC has what's called "partial penetrance" meaning not all individuals with the mutated gene will be noticeably affected. Some may have no outward signs of myotonia, or might only have it under certain conditions, which might never occur.

Myotonia Congenita can be sensitive to the affects of certain sex related hormones though. Men are usually more severely affected than women, and the symptoms of the disorder often worsen in pregnancy, so maybe there is something about the mutation in your family that makes the symptoms more severe in women...that is just speculation though.

Type of Myotonia: Becker

Country: USA