My wife has myotonia congenita. In whole her family only my wife has shown the symptoms of myotonia congeita. first the doctor said she is AR(autosomal recessive or Becker's) type but after examining her father the doctor said possibly her father also has the disease but with very mild symptoms that himself never thought of being affected. Now we are not sure which one she is.
My wife is pregnant now. I know if she is AR type there is no chance that my child be affected. But the question is if she be Thomson's type and my child got affected, what is the chance that my child show severe symptoms or is there any rule that the child of affected mother shows more severe symptoms?

Type of Myotonia: not exactly determined

Country: Iran

Mohammad,

Congratulations! I can understand how you would be concerned if her father also has myotonia congenita.

If her father does have the condition and it turns out to be Thomsen's instead of Becker's, then the baby would have a 50% chance of inheriting it. In myotonic muscular dystrophy it is true that if the mother is the one with the defective gene then the baby can be born with severe weakness and will usually be much worse than if the father was the one contributing the mutation.

However in myotonia congenita that is not the case. The genetic defect is very different. Even though we have Thomsen's in my family, my mother, who was the one with MC, never had any symptoms. My sister and I both inherited the mutation. My sister has very mild MC, but I had severe myotonia when I was younger. I have two daughters with it, one is fairly mild, the other severe. So it can definitely vary within families. Other factors can influence the symptoms. For instance when I was in high school my home was sprayed monthly with pesticide. That's when I got much worse...my sister had already graduated by then and was not living at home so she was not affected by it.

Your wife will probably be much stiffer during her pregnancy and that is very normal. If you do a search on pregnancy above, you'll find quite a few posts discussing it. There is no problem with childbirth as long as the doctors don't use general anesthesia for a Cesarean if it is necessary. Her doctor needs to be sure the notes show that she needs to avoid certain anesthetics. It sounds like he is familiar with the condition and will be careful.

If you would like to have your wife tested, there is a lab in Germany that accepts blood samples from all over the world and will test for free. You need to join the Periodic Paralysis Association at http://PeriodicParalysis.org (it's free to join). Once you are a member, you can go the Genetic Testing section and print out the forms for your doctor to sign. The only cost to you is shipping the sample to Germany. It will take several months to get the results, but at least you will know for sure which type she has, and then you can get your baby tested for that particular mutation or mutations and not wonder for years if he or she is affected.

Jan

Type of Myotonia: Thomsen's

Country: US