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Disease Profile

Myotonic dystrophy

Prevalence
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.
1-9 / 100 000

3,310 - 29,790

US Estimated

1-9 / 100 000

5,135 - 46,215

Europe Estimated

Age of onset

-

ICD-10

G71.1

Inheritance

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

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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

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X-linked
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.

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

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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.

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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.

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Not applicable

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Other names (AKA)

Dystrophia myotonica; Myotonia atrophica; Myotonia dystrophica

Categories

Musculoskeletal Diseases

Summary

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] 

Symptoms

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]

Cause

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]

Diagnosis

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." 

Treatment

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

Organizations

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

        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

            References

            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; https://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. https://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. https://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.

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