Myotonia Congenita

What is myotonia congenita?

Myotonia congenita is a rare, inherited condition that affects muscle movement. People with myotonia congenita can’t relax their muscles quickly after using them, which causes muscle stiffness. They can have muscle stiffness in any or all muscles in their body. Most people start having symptoms in early childhood. 

Myotonia congenita is caused by variants (also called mutations) in the CLCN1 gene. This gene normally controls how electrical signals turn muscle cells on and off, which is important for muscle movement. When the CLCN1 gene doesn’t work properly, muscles take longer to relax, creating stiffness.

Symptoms of myotonia congenita

Myotonia congenita causes muscle stiffness, often in the legs. The stiffness usually happens when a person starts moving suddenly after rest and can make walking difficult. Stiffness in other muscles may affect chewing or swallowing.

Some people with myotonia congenita may also have muscle cramps or unusually large or strong muscles. Even though symptoms can make some daily tasks more difficult, most people with myotonia congenita live long, healthy lives.

Types of myotonia congenita

There are two types of myotonia congenita: Becker disease and Thomsen disease, named after the doctors who first described these conditions. Each is caused by a CLCN1 gene variant.

Becker disease

Even though both types are rare, Becker disease is the more common type of myotonia congenita. It usually causes worse symptoms than Thomsen disease. 

Becker disease usually starts in middle childhood, before the teen years. It can cause muscle stiffness and weakness, which can get worse over time.

Thomsen disease

Thomsen disease is a very rare type of myotonia congenita diagnosed much earlier, in the first few years of life. Children with Thomsen disease have muscle stiffness, but it is usually milder than in Becker disease.

Who is more likely to get myotonia congenita?

Family members of people with myotonia congenita are more likely to have the condition because it is inherited. Parents pass it to their children through an abnormal version of the CLCN1 gene.

In most cases, including in Becker disease, myotonia congenita is inherited in an autosomal recessive pattern. This means that to get the disease, a person must inherit both copies of a CLCN1 gene variant, one from each parent. The parents of a person with an autosomal recessive condition each carry one copy of the altered gene, but they typically don’t show signs and symptoms of the condition. 

In rarer cases, such as in Thomsen disease, myotonia congenita can be inherited in an autosomal dominant pattern. In these cases, a person only needs to inherit one copy of a CLCN1 gene variant to get the disease. The gene variant could come from either parent.

If you think myotonia congenita may run in your family, or that you might have a copy of the CLCN1 gene variant, talk to a doctor about genetic testing. Genetic testing can determine whether a person can pass on the condition to their children.

How is myotonia congenita diagnosed and treated?

Diagnosing myotonia congenita

Doctors diagnose myotonia congenita based on symptoms and genetic testing. Genetic tests show whether a person or a family member has a gene variant that causes myotonia congenita. This is important because some people may have mild symptoms or not realize they have the condition. Certain medicines and types of anesthesia can cause dangerous muscle reactions in people with myotonia congenita. 

Learn more about neurological diagnostic tests and procedures.

Treating myotonia congenita

Most people with myotonia congenita don't need treatment. Stiff muscles usually relax with exercise or light movement, especially after resting. Physical therapy may also help relieve symptoms.

Some medicines that help control electrical signals in muscles may help treat myotonia congenita symptoms that don’t go away with exercise or light movement. These medicines help muscles relax to reduce stiffness.

What are the latest updates on myotonia congenita?

The National Institutes of Health (NIH), which includes NINDS, is the leading federal funder of research on the brain and nervous system, including disorders such as myotonia congenita. NIH supports new research to better understand, diagnose, and treat myotonia congenita.

For more information on research about myotonia congenita, check NIH RePORTER, a searchable database of current and past research projects funded by NIH and other federal agencies. RePORTER also has links to publications and resources from these projects. 

For research articles and summaries on myotonia congenita, search PubMed, which contains citations from medical journals and other sites.

How can I or my loved one help improve care for people with myotonia congenita?

Consider participating in a clinical trial so clinicians and scientists can learn more about myotonia congenita and related disorders. Clinical research with human study participants helps researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.

All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities. This helps make sure that study results apply to as many people as possible and that treatments will be safe and effective for everyone who will use them.

For information about participating in clinical research, visit the NINDS Clinical Trials site and NIH Clinical Research Trials and You. Learn about clinical trials currently looking for people with myotonia congenita at ClinicalTrials.gov, a searchable database of current and past clinical studies and research results.

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