Sarah, it is hereditary. There are two types. Thomsen's MC is dominantly inherited, which means you only need to have one parent with a mutation in the chloride ion channel gene in order to have symptoms. The other type, Becker's MC, is recessive, so you need to have two mutations, one from each parent, to have symptoms. If you are a carrier, you won't be affected.

If your father has the dominant form, then there are probably other family members who have had some symptoms. Myotonia itself (the mutation) does not cause pain. Many people with myotonia congenita have no pain in their muscles. But pushing against the muscles when you are stiff will damage them and that is what causes the pain. You can also tear tendons and ligaments. Some people are much more susceptible to this than others.

Just having muscle pain does not mean you have myotonia. What you're describing sounds a lot like fibromyalgia, and to get that diagnosed you would see a rheumatologist. Myotonia is a delayed relaxation of the muscle, so when you make a fist you can't open your hand again immediately. Or if you get out of a chair, you can't start walking right away or you'll fall. It's the same thing that fainting goats have.

It's very easy to find out if you have myotonia. Since your father was already diagnosed, you can go to a neurologist and ask to have a DNA test or and EMG, which is a small needle inserted into the muscle to listen to the electrical activity. If you have a myotonia caused by a defect in the CLCN1 gene, it will show up. There are also myotonias in the sodium channel gene called SCN4A. Your doctor can include that in the DNA testing.

This is one of the top myotonia specialists in the UK. Perhaps you can get a referral to find out for sure if you have MC:

Prof Michael Hanna

Jan

Type of Myotonia: Thomsen's

Country: US

Hi Jan thanks for the reply. My father's mother (my grandmother) has fibromyalgia. Do you know if that could of been passed down to me? Thanks again.

Type of Myotonia: .

Country: uk

Sarah, fibromyalgia does seem to run in families. It is much more common in females.

This is a good information page about fibromyalgia:
Fibromyalgia Q&A

There is a condition called Ehlers-Danlos Syndrome which is hereditary and the hypermobility type is strongly associated with fibromyalgia. Many people with this condition are "double-jointed" or very flexible because of a defect in collagen synthesis. This page shows one of the criteria for diagnosis:
Beighton Score

If any of that seems to fit, I would suggest seeing a rheumatologist.

Jan

Type of Myotonia: Thomsen's

Country: US