Return to Website

Myotonia Congenita Forum

 

This forum has been closed for comments.  You can still search archived messages.

 

Visit  the Non-Dystrophic Myotonias  Facebook Group

Myotonia Congenita Forum
Start a New Topic 
Author
Comment
View Entire Thread
Re: My dad has Thomsens disease and I have a question about inheritance

Welcome! If you and your dad had DNA testing and not just an EMG to determine that he has Thomsen's and you don't, then you would not pass on a mutation to your children. There are a few mutations associated with Thomsen's that can be either dominant or recessive in their behavior, so that's why it's important to verify that you did not inherit a mutation with DNA testing.

In general, with Thomsen's MC it only takes one copy of a mutation to have symptoms. You would have a 50% chance of getting that mutation from your father. If you did, then your children would have a 50% chance of having the mutation also.

With Becker's MC, it takes a copy from each parent rather than just one. So your children might have a mutation, but if they only have one copy, then they would not have symptoms. For a person to have symptoms, they can either have two copies of the same mutation, or two different ones associated with Becker's.

This website has a chart that shows how both types are inherited:
http://www.socialstyrelsen.se/rarediseases/myotoniacongenita

Jan

Type of Myotonia: Thomsen's

Country: US

Re: My dad has Thomsens disease and I have a question about inheritance

Thank you so much for the swift reply!

Thank you, you just confirmed what had crossed my mind not too long ago; I think I will go ahead and have DNA testing done to be certain (my dad already has his done and he was verified to have it). I have never experienced any symptoms (at least I don't think so) and I am now 21, but as you said the DNA testing will be the tell all.

I'm not sure if you would know, but what are the chances that I did inherit a mutation if I have thus far had no symptoms/troubles? Is it possible I could have it/have a form of it and be asymptomatic?

Also, how exactly is DNA testing done?

thank you so much again,

Ashleigh

Type of Myotonia: Thomsens

Country: United States

Re: My dad has Thomsens disease and I have a question about inheritance

Since you already know your dad's mutation, you can have the lab check for that particular mutation which is much quicker and much less expensive (that makes the insurance companies more likely to pay for it). This is one of the two labs in the US that does the testing:

Fullerton Genetics Lab

If you make an appointment with an MDA clinic, they will probably be able to order the testing through Athena Diagnostics Lab. You can also ask for a referral from your doctor to a geneticist who can order testing.

It is possible for you to have a mutation without any symptoms. As I mentioned, there are a few mutations associated with Thomsen's that seem to be able to behave either way. My family has one of those (the notation is G230E). My mother never had any symptoms except anesthesia sensitivity. Her sister had no symptoms but my cousin did. My sister only had very mild stiffness. So it is worth getting tested, primarily so that you will know if you need to use the anesthesia protocol for myotonia, but also so that you will know abut the chances of your children inheriting the mutation.

It's unlikely that you have myotonia congenita since you haven't noticed any symptoms (they usually show up in childhood), but just to be sure, I think DNA testing is a good idea. It's just a simple blood test and you will get the results within a few weeks.

Jan

Type of Myotonia: Thomsen's

Country: US

Re: My dad has Thomsens disease and I have a question about inheritance

Hi,

the code for my disorder is c.920T>C (p.Phe307Ser). I am the only one in family who has got it, but the doctor and lab say it is known to be both dominant and recessive so that I can never really know which type I have got. And when I check on internet they also say that it could be both. This is very confusing.
someone out there with the same mutation?

Type of Myotonia: thomsen

Country: germany

Re: My dad has Thomsens disease and I have a question about inheritance

As your doctor said, yours is one of the mutations that can go either way. Here's an article about it (the notation is F307S):

Variable Penetrance of Mutations

My family has one of those types, although not the same mutation. So one of your parents has the mutation, but it didn't cause symptoms. The same was true for me...my mother had no symptoms. Variable penetrance means the mutation can get passed through several generations and cause symptoms in some and not in others. They don't seem to know what makes the difference. It may have to do with other genetic factors that further inhibit the chloride ion channel.

So if you have children, they will have a 50% chance of inheriting the gene, but it would be impossible to know whether it would cause symptom of myotonia congenita. It is important for your family members to have their anesthesiologists use the protocol for myotonia (malignant hyperthermia) and monitor potassium during surgery. Just carrying the gene will be enough to make them susceptible to a reaction. Dr. Lehmann-Horn's lab in Ulm can test for the mutation in other family members, even if they have no symptoms.

Here's his contact information if you don't have it:

Frank Lehmann-Horn M.D. Ph.D.
Hertie Senior Research Professor
Division of Neurophysiology
University of Ulm
Albert-Einstein-Allee 11
89081 Ulm/Germany
Phone: +49 (0)731 / 500 - 23250
Fax: +49 (0)731 / 500 - 23260

Jan

Type of Myotonia: Thomsen's

Country: US