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Genetic and Rare Diseases Information Center (GARD)

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Myotonia congenita autosomal dominant


Other Names for this Disease

  • Autosomal dominant myotonia congenita
  • THD
  • Thomsen disease
  • Thomsen's disease
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Your Question

My daughter has myotonia congenita even though there is no family history of the condition. My husband and I are first cousins. She is now married to a man who is not a blood relative. What are their chances of having a child with the condition? 

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is myotonia congenita?

Myotonia congenita is a genetic condition characterized by the inability of the skeletal muscles to quickly relax after a voluntary movement.  The symptoms associated with the condition typically appear in childhood and vary from person to person. There are two forms of the disorder:  Becker type, which is the most common form; and Thomsen disease, which is a rare and milder form. [1] Both conditions are caused by mutations in the CLCN1 gene.  However, the conditions have different modes of inheritance.  The Becker type is inherited in an autosomal recessive fashion, and the Thomsen type is inherited in an autosomal dominant manner. [2]
Last updated: 7/29/2010

How can I find out which form of myotonia congenita is present in my family?

Because mutations in the CLCN1 gene can cause either the Becker form or Thomsen form, doctors usually rely on characteristic signs and symptoms to distinguish the two forms of myotonia congenita. These conditions are distinguished by the severity of their symptoms and the way they are inherited in a family. Becker disease usually appears later in childhood than Thomsen disease and causes more severe muscle stiffness, particularly in males. People with Becker disease often experience temporary attacks of muscle weakness, particularly in the arms and hands, brought on by movement after periods of rest. They may also develop mild, permanent muscle weakness over time. This muscle weakness is not seen in people with Thomsen disease. [2]
Last updated: 6/2/2008

What is autosomal dominant inheritance?

Autosomal dominant inheritance is when one mutated copy of the gene that causes a disorder in each cell is needed for a person to be affected. Autosomal dominant conditions may occur for the first time in a person in a family due to a spontaneous gene mutation, or these conditions may be inherited from an affected parent. When a person with an autosomal dominant disorder has a child, there is a 50% chance that their child will inherit the condition.[3]
Last updated: 12/3/2009

What is autosomal recessive inheritance?

Autosomal recessive inheritance refers to the inheritance pattern in which two mutated copies of the gene that causes a disorder are present in each cell. An affected person usually has unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers). Autosomal recessive disorders are typically not seen in every generation of an affected family. When two people who are carriers of an autosomal recessive condition have a child, there is a 25% (1 in 4) chance that the child will be affected.[3]

Last updated: 2/18/2009

What is the chance that my daughter's children will also have myotonia congenita? 

To determine the chance that your daughter's children will also have myotonia congenita, it is important to know whether she has the Thomsen or Becker type. We suggest that she speak to her doctor about obtaining a more specific diagnosis. Because you mentioned that you and your husband are first cousins and are unaffected, it is more likely that she has the Becker type, which is inherited in an autosomal recessive manner. As mentioned above, both parents need to have a genetic change in the CLCN1 gene to have a child with myotonia congenita. Because your daughter has myotonia congenita, she has two copies of the mutated CLCN1 gene in the cells of her body. She will pass on one of these mutated copies to her children. If your daughter's husband is not a carrier, then their children will be unaffected carriers of myotonia congenita. If your daughter's husband is a carrier, then there is a 50% (1 in 2) chance with each pregnancy that they would have a child with myotonia congenita. We recommend that your daughter have a genetics consultation to learn more about her husband's chance of being a carrier and genetic testing options.[2]
Last updated: 6/2/2008

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:

Last updated: 7/17/2013

References
Other Names for this Disease
  • Autosomal dominant myotonia congenita
  • THD
  • Thomsen disease
  • Thomsen's disease
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.