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Disease Profile

Myotonia congenita

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Thomsen and Becker disease


Congenital and Genetic Diseases; Nervous System Diseases


Myotonia congenita is a genetic disease characterized by the inability of the skeletal muscles to quickly relax after voluntary movements. Symptoms typically begin in childhood and vary from person to person. They may include muscle stiffness, muscle weakness, and attacks of weakness brought on by movement after rest. There are two forms of myotonia congenita: Becker disease, which is the most common and severe, generalized form; and Thomsen disease, which is a rare and milder form.[1] Both forms are caused by mutations in the CLCN1 gene. The Becker type is inherited in an autosomal recessive manner, and the Thomsen type is inherited in an autosomal dominant manner.[2] Treatment may include medication for muscle stiffness, such as mexiletine, carbamazepine, or phenytoin. Exercise may temporarily alleviate myotonia. People with myotonia congenita may be at increased risk for harmful side effects of anesthesia. Therefore, it is recommended that relatives of a person with the disease are tested during childhood.[3]


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
EMG abnormality
5%-29% of people have these symptoms
Muscle ache
Muscle pain

[ more ]

1%-4% of people have these symptoms
Muscle stiffness
Muscle weakness
Muscular weakness
Myotonia with warm-up phenomenon
Percussion myotonia
Skeletal muscle hypertrophy
Increased skeletal muscle cells
Percent of people who have these symptoms is not available through HPO
Autosomal dominant inheritance
Autosomal recessive inheritance
Childhood onset
Symptoms begin in childhood
Poor swallowing
Swallowing difficulties
Swallowing difficulty

[ more ]

EMG: myotonic runs
Handgrip myotonia
Lid lag on downgaze
Muscle hypertrophy of the lower extremities


Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.


    Treatment for myotonia congenita depends on the symptoms and severity in each person. People with mild symptoms may just need to modify their activities. Those with more severe muscle stiffness might consider or need sodium channel blockers or other medications to relieve symptoms. Medication options may include:

    • Mexiletine this is a sodium channel blocker and is the best documented treatment option. It may significantly reduce muscle stiffness.
    • Phenytoin or carbamazepine these are anticonvulsants that have been reported to help symptoms in some people.
    • Quinine (an antimalarial), dantrolene (a muscle relaxant), or acetazolamide (a diuretic) may help symptoms in some cases.

    Exercise is known to temporarily relieve myotonia. Some people with myotonia congenita have reported more long-term relief with gymnastics, but this has not been studied in controlled trials. Anesthesia should be used with caution in people with myotonia congenita.[3]

    Management Guidelines

    • Project OrphanAnesthesia is a project whose aim is to create peer-reviewed, readily accessible guidelines for patients with rare diseases and for the anesthesiologists caring for them. The project is a collaborative effort of the German Society of Anesthesiology and Intensive Care, Orphanet, the European Society of Pediatric Anesthesia, anesthetists and rare disease experts with the aim to contribute to patient safety.


      Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

      Organizations Supporting this Disease

        Organizations Providing General Support

          Learn more

          These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

          Where to Start

          • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.
          • Muscular Dystrophy Association has information and resources about Myotonia congenita. Please click on the link to access this resource.
          • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

            In-Depth Information

            • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
            • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
            • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
              Myotonia congenita, autosomal recessive (Becker disease)
              Myotonia congenita, autosomal dominant (Thomsen disease)
            • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.


              1. NINDS Myotonia Congenita Information Page. National Institute of Neurological Disorders and Stroke (NINDS). October 18, 2015; https://www.ninds.nih.gov/Disorders/All-Disorders/Myotonia-Congenita-Information-Page.
              2. Myotonia congenita. Genetics Home Reference (GHR). April 2007; https://ghr.nlm.nih.gov/condition/myotonia-congenita.
              3. Dunø M & Colding-Jørgensen E. Myotonia Congenita. GeneReviews. 2015; https://www.ncbi.nlm.nih.gov/books/NBK1355/.

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