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Genetics Home Reference: your guide to understanding genetic conditions
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Myotonia congenita

Reviewed April 2007

What is myotonia congenita?

Myotonia congenita is a disorder that affects muscles used for movement (skeletal muscles). Beginning in childhood, people with this condition experience bouts of sustained muscle tensing (myotonia) that prevent muscles from relaxing normally. Although myotonia can affect any skeletal muscles, including muscles of the face and tongue, it occurs most often in the legs. Myotonia causes muscle stiffness that can interfere with movement. In some people the stiffness is very mild, while in other cases it may be severe enough to interfere with walking, running, and other activities of daily life. These muscle problems are particularly noticeable during movement following a period of rest. Many affected individuals find that repeated movements can temporarily alleviate their muscle stiffness, a phenomenon known as the warm-up effect.

The two major types of myotonia congenita are known as Thomsen disease and Becker disease. These conditions are distinguished by the severity of their symptoms and their patterns of inheritance. 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.

How common is myotonia congenita?

Myotonia congenita is estimated to affect 1 in 100,000 people worldwide. This condition is more common in northern Scandinavia, where it occurs in approximately 1 in 10,000 people.

What genes are related to myotonia congenita?

Mutations in the CLCN1 gene cause myotonia congenita.

The CLCN1 gene provides instructions for making a protein that is critical for the normal function of skeletal muscle cells. For the body to move normally, skeletal muscles must tense (contract) and relax in a coordinated way. Muscle contraction and relaxation are controlled by the flow of charged atoms (ions) into and out of muscle cells. Specifically, the protein produced from the CLCN1 gene forms a channel that controls the flow of negatively charged chlorine atoms (chloride ions) into these cells. The main function of this channel is to stabilize the cells' electrical charge, which prevents muscles from contracting abnormally.

Mutations in the CLCN1 gene alter the usual structure or function of chloride channels. The altered channels cannot properly regulate ion flow, reducing the movement of chloride ions into skeletal muscle cells. This disruption in chloride ion flow triggers prolonged muscle contractions, which are the hallmark of myotonia.

Related Gene(s)

Changes in this gene are associated with myotonia congenita.

  • CLCN1

How do people inherit myotonia congenita?

The two forms of myotonia congenita have different patterns of inheritance. Thomsen disease is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person has one parent with the condition.

Becker disease is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition.

Because several CLCN1 mutations can cause either Becker disease or Thomsen disease, doctors usually rely on characteristic signs and symptoms to distinguish the two forms of myotonia congenita.

Where can I find information about diagnosis or management of myotonia congenita?

These resources address the diagnosis or management of myotonia congenita and may include treatment providers.

  • Gene Review: Myotonia Congenita (http://www.ncbi.nlm.nih.gov/books/NBK1355)
  • Genetic Testing Registry: Congenital myotonia, autosomal dominant form (http://www.ncbi.nlm.nih.gov/gtr/conditions/C2936781)
  • Genetic Testing Registry: Congenital myotonia, autosomal recessive form (http://www.ncbi.nlm.nih.gov/gtr/conditions/C0751360)
  • Genetic Testing Registry: Myotonia congenita (http://www.ncbi.nlm.nih.gov/gtr/conditions/C0027127)
  • MedlinePlus Encyclopedia: Myotonia congenita (http://www.nlm.nih.gov/medlineplus/ency/article/001424.htm)

You might also find information on the diagnosis or management of myotonia congenita in Educational resources and Patient support.

General information about the diagnosis (http://ghr.nlm.nih.gov/handbook/consult/diagnosis) and management (http://ghr.nlm.nih.gov/handbook/consult/treatment) of genetic conditions is available in the Handbook. Read more about genetic testing (http://ghr.nlm.nih.gov/handbook/testing), particularly the difference between clinical tests and research tests (http://ghr.nlm.nih.gov/handbook/testing/researchtesting).

To locate a healthcare provider, see How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

Where can I find additional information about myotonia congenita?

You may find the following resources about myotonia congenita helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for myotonia congenita?

  • Congenital myotonia

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines (http://ghr.nlm.nih.gov/ConditionNameGuide) and How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.

What if I still have specific questions about myotonia congenita?

Ask the Genetic and Rare Diseases Information Center (https://rarediseases.info.nih.gov/gard).

What glossary definitions help with understanding myotonia congenita?

autosomal ; autosomal dominant ; autosomal recessive ; cell ; channel ; chloride ; chloride channels ; chloride ion ; congenital ; contraction ; gene ; inheritance ; inherited ; ions ; muscle cells ; myotonia ; protein ; recessive ; skeletal muscle

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

References

  • Chrestian N, Puymirat J, Bouchard JP, Dupré N. Myotonia congenita--a cause of muscle weakness and stiffness. Nat Clin Pract Neurol. 2006 Jul;2(7):393-9; quiz following 399. (http://www.ncbi.nlm.nih.gov/pubmed/16932590?dopt=Abstract)
  • Colding-Jørgensen E. Phenotypic variability in myotonia congenita. Muscle Nerve. 2005 Jul;32(1):19-34. Review. (http://www.ncbi.nlm.nih.gov/pubmed/15786415?dopt=Abstract)
  • Gene Review: Myotonia Congenita (http://www.ncbi.nlm.nih.gov/books/NBK1355)
  • Pusch M. Myotonia caused by mutations in the muscle chloride channel gene CLCN1. Hum Mutat. 2002 Apr;19(4):423-34. Review. (http://www.ncbi.nlm.nih.gov/pubmed/11933197?dopt=Abstract)
  • Sun C, Tranebjaerg L, Torbergsen T, Holmgren G, Van Ghelue M. Spectrum of CLCN1 mutations in patients with myotonia congenita in Northern Scandinavia. Eur J Hum Genet. 2001 Dec;9(12):903-9. Erratum in: Eur J Hum Genet. 2010 Feb;18(2):264. (http://www.ncbi.nlm.nih.gov/pubmed/11840191?dopt=Abstract)
  • Zhang J, George AL Jr, Griggs RC, Fouad GT, Roberts J, Kwieciński H, Connolly AM, Ptácek LJ. Mutations in the human skeletal muscle chloride channel gene (CLCN1) associated with dominant and recessive myotonia congenita. Neurology. 1996 Oct;47(4):993-8. (http://www.ncbi.nlm.nih.gov/pubmed/8857733?dopt=Abstract)

 

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.

 
Reviewed: April 2007
Published: September 1, 2015