National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Myotonic dystrophy

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Other Names:
Dystrophia myotonica; Myotonia atrophica; Myotonia dystrophica
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Subtypes:
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Myotonic dystrophy is a disease that affects the muscles and other body systems. It is the most common form of muscular dystrophy that begins in adulthood, usually in a person’s 20s or 30s. This disease is characterized by progressive muscle loss and weakness. Myotonic dystrophy may be further classified into two types, and the two types may affect different muscles. People with myotonic dystrophy usually have prolonged muscle tensing (myotonia) and are not able to relax certain muscles after use. The severity of the disease may vary among affected people, even among members of the same family.[1][2]

Myotonic dystrophy is caused by mutations (changes) in the DMPK gene or the CNBP (ZNF9) gene depending on the specific type of myotonic dystrophy. The disease is inherited in an autosomal dominant manner.[1] Myotonic dystrophy may be diagnosed when a healthcare provider observes signs and symptoms of the disease, and the diagnosis may be confirmed with tests of muscle function and genetic testing.[3] Treatment is based on each person’s specific signs and symptoms and may include physical therapy, pain management with medication, and consultation with specialists.[3][4] 
Last updated: 8/21/2017
Signs and symptoms of myotonic dystrophy often begin in a person’s 20s or 30s but can begin at any age. Symptoms often include progressive muscle weakness, stiffness, tightness, and wasting. There are two types of myotonic dystrophy: myotonic dystrophy type 1 and myotonic dystrophy type 2. The symptoms in people with myotonic dystrophy type 2 tend to be milder than in those with type 1, but the symptoms may overlap. People with myotonic dystrophy type 1 typically experience involvement of the legs, hands, neck, and face, while people with myotonic dystrophy type 2 typically experience involvement of the neck, shoulders, elbows, and hips. The severity of symptoms can vary widely among affected people. [1]

Other signs and symptoms of myotonic dystrophy can include cataracts, type-2 diabetes, and cardiac conduction defects (irregular electrical control of the heartbeat). Some affected men also have hormonal changes that may cause balding or infertility.[1][5]

In some cases, babies are born with a variation of myotonic dystrophy type 1 called congenital myotonic dystrophy. Symptoms of congenital myotonic dystrophy are present from birth and include weakness of all muscles, breathing problems, clubfeet, developmental delays and intellectual disabilities.[1][4]
Last updated: 8/21/2017
Myotonic dystrophy is caused by mutations (changes) in either the DMPK gene (in type 1) or the CNBP (ZNF9) gene (in type 2). The specific kinds of mutations found in both types of myotonic dystrophy are trinucleotide repeat expansions. These types of mutations occur when a piece of DNA is abnormally repeated a number of times, which makes the gene unstable. The mutated gene makes an altered version of messenger RNA (mRNA), which is a copy of the gene that is normally used for protein production. The abnormal mRNA forms clumps inside the cell that interfere with the production of many proteins. These changes prevent cells in muscles and other tissues from functioning normally, leading to the signs and symptoms of myotonic dystrophy.[1]

The exact functions of the DMPK and CNBP genes are not well understood. DMPK may play a role in communication within cells, specifically in cells of the heart, brain, and skeletal muscles. The CNBP gene gives the body directions to make a protein found mainly in the cells of the heart and skeletal muscles, where it is thought to regulate the activities of other genes.[1]
Last updated: 8/21/2017
Myotonic dystrophy (DM) is inherited in an autosomal dominant pattern.[1] This means that one copy of the altered gene in each cell of the body is enough to cause symptoms of the disease. We inherit one copy of each gene from our mother and the other from our father. Therefore, when a person with myotonic dystrophy goes on to have children, there is a 50% chance that each child will have myotonic dystrophy. 

Any person who has myotonic dystrophy can pass the mutation on to his or her children, whether the children are male or female. Myotonic dystrophy type 1 exhibits an unusual genetic pattern called anticipation.[4] Anticipation means the signs and symptoms of a genetic disease begin earlier in life and become more severe as the disease is passed on through generations. Congenital myotonic dystrophy type 1 occurs only when the disease is inherited from the mother.
Last updated: 1/3/2018
Myotonic dystrophy is diagnosed by doing a physical exam. A physical exam can identify the typical pattern of muscle wasting and weakness of the jaw and neck muscles and the presence of myotonia. Men may have frontal balding.[3][4]

There are several laboratory tests that can be used to clarify the clinical diagnosis of myotonic dystrophy. One test, called electromyography (EMG), involves inserting a small needle into the muscle. The electrical activity of the muscle is studied and usually shows characteristic patterns of myotonic dystrophy.[3] Other laboratory tests may include a muscle biopsy, which can be used to determine if the muscle fibers are weaker than they should be (atrophied), or a blood test to determine if there are elevated levels of certain muscle enzymes.[3][6]

The definitive test for myotonic dystrophy is a genetic test. For this test, a blood or saliva sample is analyzed to determine if there is a mutation in the DMPK or CNBP (ZNF9) genes.[3][4][7]

The University of Washington provides more information on genetic testing for myotonic dystrophy in their publication titled, "Myotonic Dystrophy: Making an Informed Choice About Genetic Testing." 
Last updated: 4/20/2018
There is currently no cure or specific treatment for myotonic dystrophy.[5] Treatment is aimed at managing symptoms of the disease.[7] Routine physical activity appears to help maintain muscle strength and endurance and to control musculoskeletal pain.[3] Canes, braces, walkers, and scooters can help as muscle weakness progresses.[5]

There are also medications that can lessen pain associated with myotonic dystrophy.[5] Pain management can be achieved through the use of medications prescribed by a doctor.[4][8] Heart problems associated with myotonic dystrophy can be treated through the insertion of a pacemaker, medications, and regular monitoring of cardiac function. Cataracts can be surgically removed. Testosterone replacement therapy may be used to treat infertility in males.[8]

Current research is focusing on how we might be able to one day use gene-editing technology or other treatments to remove the clumps of RNA that cause the symptoms of myotonic dystrophy. However, this therapy is not yet possible in humans.[9][10]

GeneReviews has more detailed information about the management of myotonic dystrophy type 1 and type 2. 
Last updated: 8/21/2017
The long-term outlook (prognosis) for each person with myotonic dystrophy (including life expectancy) may depend on the type of myotonic dystrophy and the specific medical problems present. Myotonic dystrophy is a progressive disease, meaning that symptoms worsen as a person gets older.[11]

Although evidence is limited, life expectancy appears to be reduced for people with myotonic dystrophy type 1 (DM1). The most common causes of death in people with DM1 are respiratory and cardiac (heart) symptoms. An increased risk of death may be associated with younger age of onset, more severe muscle weakness, and cardiac conduction defects. People with more mild symptoms of DM1 may have a normal lifespan.[12]

Definitive information about prognosis in people with myotonic dystrophy type 2 is limited, but the condition generally runs a milder course. People with myotonic dystrophy type 2 may have a normal lifespan.[12] While mobility may be impaired at an early age, the ability to walk is often retained until around 60-years-old.[3]
Last updated: 8/22/2017

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • ClinicalTrials.gov lists trials that are related to Myotonic dystrophy. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.

    Please note: Studies listed on the ClinicalTrials.gov website are listed for informational purposes only; being listed does not reflect an endorsement by GARD or the NIH. We strongly recommend that you talk with a trusted healthcare provider before choosing to participate in any clinical study.
  • The Research Portfolio Online Reporting Tool (RePORT) provides access to reports, data, and analyses of research activities at the National Institutes of Health (NIH), including information on NIH expenditures and the results of NIH-supported research. Although these projects may not conduct studies on humans, you may want to contact the investigators to learn more. To search for studies, enter the disease name in the "Text Search" box. Then click "Submit Query".

Patient Registry

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

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

In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Myotonic dystrophy. Click on the link to view a sample search on this topic.
  • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles on myotonic dystrophy type 1 and myotonic dystrophy type 2. These articles describe the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.

Selected Full-Text Journal Articles

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know.

  1. Myotonic dystrophy. Genetics Home Reference (GHR). November 2010; https://ghr.nlm.nih.gov/condition/myotonic-dystrophy.
  2. Myotonic Dystrophy 1; DM1. Online Mendelian Inheritance in Man. July 6, 2017; https://www.omim.org/entry/160900.
  3. Dalton JC, Ranum LPW, and Day JW. Myotonic Dystrophy Type 2. GeneReviews. July 3, 2013; http://www.ncbi.nlm.nih.gov/books/NBK1466/.
  4. Bird TD. Myotonic Dystrophy Type 1. GeneReviews. October 22, 2015; https://www.ncbi.nlm.nih.gov/books/NBK1165/.
  5. Learning About Myotonic Dystrophy. National Human Genome Research Institute (NHGRI). June 5, 2017; https://www.genome.gov/25521207/.
  6. Bird TD. Myotonic Dystrophy. National Organization for Rare Disorders. 2017; https://rarediseases.org/rare-diseases/dystrophy-myotonic/.
  7. O’Sullivan Smith C, Bennett RL, and Bird TD. Myotonic Dystrophy: Making an Informed Choice About Genetic Testing. Department of Neurology, University of Washington School of Medicine. http://depts.washington.edu/neurolog/images/neurogenetics/myotonic.pdf. Accessed 8/16/2017.
  8. Adult-Onset MMD1/MMD2 and Juvenile-Onset MMD1. Muscular Dystrophy Association (MDA). 2017; https://www.mda.org/disease/myotonic-muscular-dystrophy/medical-management/adult-mmd1-mmd2-juvenile-mmd1. Accessed 8/16/2017.
  9. Batra R, Nelles DA, Pirie E, Blue SM, Marina RJ, Wang H, Chaim IA, Thomas JD, Zhang N, Nguyen V, Aigner S, Markmiller S, Xia G, Corbett KD, Swanson MS, and Yeo GW. Elimination of Toxic Microsatellite Repeat Expansion RNA by RNA-Targeting Cas9. Cell. August 8, 2017; https://www.ncbi.nlm.nih.gov/pubmed/28803727.
  10. Konieczny P, Selma-Soriano E, Rapisarda AS, Fernandez-Costa JM, Perez-Alonso M, and Artero R. Myotonic dystrophy: candidate small molecule therapeutics. Drug Discovery Today. August 2, 2017; https://www.ncbi.nlm.nih.gov/pubmed/28780071.
  11. Managing DM: FAQs. Myotonic Dystrophy Foundation. http://www.myotonic.org/what-dm/faqs. Accessed 8/16/2017.
  12. Darras BT and Chad DA. Myotonic dystrophy: Etiology, clinical features, and diagnosis. UpToDate. June 6, 2017; https://www.uptodate.com/contents/myotonic-dystrophy-etiology-clinical-features-and-diagnosis#H191953850.