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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®

Myotonic dystrophy

Reviewed November 2010

What is myotonic dystrophy?

Myotonic dystrophy is part of a group of inherited disorders called muscular dystrophies. It is the most common form of muscular dystrophy that begins in adulthood.

Myotonic dystrophy is characterized by progressive muscle wasting and weakness. People with this disorder often have prolonged muscle contractions (myotonia) and are not able to relax certain muscles after use. For example, a person may have difficulty releasing their grip on a doorknob or handle. Also, affected people may have slurred speech or temporary locking of their jaw.

Other signs and symptoms of myotonic dystrophy include clouding of the lens of the eye (cataracts) and abnormalities of the electrical signals that control the heartbeat (cardiac conduction defects). In affected men, hormonal changes may lead to early balding and an inability to father a child (infertility). The features of this disorder often develop during a person's twenties or thirties, although they can occur at any age. The severity of the condition varies widely among affected people, even among members of the same family.

There are two major types of myotonic dystrophy: type 1 and type 2. Their signs and symptoms overlap, although type 2 tends to be milder than type 1. The muscle weakness associated with type 1 particularly affects the lower legs, hands, neck, and face. Muscle weakness in type 2 primarily involves the muscles of the neck, shoulders, elbows, and hips. The two types of myotonic dystrophy are caused by mutations in different genes.

A variation of type 1 myotonic dystrophy, called congenital myotonic dystrophy, is apparent at birth. Characteristic features include weak muscle tone (hypotonia), an inward- and upward-turning foot (clubfoot), breathing problems, delayed development, and intellectual disability. Some of these health problems can be life-threatening.

How common is myotonic dystrophy?

Myotonic dystrophy affects at least 1 in 8,000 people worldwide. The prevalence of the two types of myotonic dystrophy varies among different geographic and ethnic populations. In most populations, type 1 appears to be more common than type 2. However, recent studies suggest that type 2 may be as common as type 1 among people in Germany and Finland.

What genes are related to myotonic dystrophy?

Myotonic dystrophy type 1 is caused by mutations in the DMPK gene, while type 2 results from mutations in the CNBP gene. The specific functions of these genes are unclear. The protein produced from the DMPK gene may play a role in communication within cells. It appears to be important for the correct functioning of cells in the heart, brain, and skeletal muscles (which are used for movement). The protein produced from the CNBP gene is found primarily in the heart and in skeletal muscles, where it probably helps regulate the function of other genes.

Similar changes in the structure of the DMPK and CNBP genes cause the two forms of myotonic dystrophy. In each case, a segment of DNA is abnormally repeated many times, forming an unstable region in the gene. The mutated gene produces an expanded version of messenger RNA, which is a molecular blueprint of the gene that is normally used to guide the production of proteins. The abnormally long messenger RNA forms clumps inside the cell that interfere with the production of many other proteins. These changes prevent muscle cells and cells in other tissues from functioning normally, which leads to the signs and symptoms of myotonic dystrophy.

Related Gene(s)

Changes in these genes are associated with myotonic dystrophy.

  • CNBP
  • DMPK

How do people inherit myotonic dystrophy?

Both types of myotonic dystrophy are 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.

As myotonic dystrophy is passed from one generation to the next, the disorder generally begins earlier in life and signs and symptoms become more severe. This phenomenon, called anticipation, has been reported with both types of myotonic dystrophy. However, the evidence for anticipation appears to be strongest in myotonic dystrophy type 1. In this form of the disorder, anticipation is caused by an increase in the length of the unstable region in the DMPK gene. It is less clear whether anticipation occurs in myotonic dystrophy type 2, and the mechanism is unknown. A longer unstable region in the CNBP gene does not appear to influence the age of onset of the disorder.

Where can I find information about diagnosis or management of myotonic dystrophy?

These resources address the diagnosis or management of myotonic dystrophy and may include treatment providers.

  • Gene Review: Myotonic Dystrophy Type 1 (
  • Gene Review: Myotonic Dystrophy Type 2 (
  • Genetic Testing Registry: Myotonic dystrophy type 2 (
  • Genetic Testing Registry: Steinert myotonic dystrophy syndrome (
  • MedlinePlus Encyclopedia: Muscular Dystrophy (
  • University of Washington: Myotonic Dystrophy: Making an Informed Choice About Genetic Testing (

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

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about myotonic dystrophy?

You may find the following resources about myotonic dystrophy 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 myotonic dystrophy?

  • dystrophia myotonica
  • myotonia atrophica
  • myotonia dystrophica

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about myotonic dystrophy?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding myotonic dystrophy?

anticipation ; atrophy ; autosomal ; autosomal dominant ; cardiac ; cell ; clubfoot ; congenital ; disability ; DNA ; gene ; hypotonia ; infertility ; inherited ; messenger RNA ; muscle cells ; muscle tone ; muscular dystrophy ; myotonia ; prevalence ; protein ; proximal ; RNA ; syndrome ; wasting

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


  • Cho DH, Tapscott SJ. Myotonic dystrophy: emerging mechanisms for DM1 and DM2. Biochim Biophys Acta. 2007 Feb;1772(2):195-204. Epub 2006 Jun 20. Review. (
  • Day JW, Ranum LP. RNA pathogenesis of the myotonic dystrophies. Neuromuscul Disord. 2005 Jan;15(1):5-16. Epub 2004 Nov 26. Review. (
  • Day JW, Ricker K, Jacobsen JF, Rasmussen LJ, Dick KA, Kress W, Schneider C, Koch MC, Beilman GJ, Harrison AR, Dalton JC, Ranum LP. Myotonic dystrophy type 2: molecular, diagnostic and clinical spectrum. Neurology. 2003 Feb 25;60(4):657-64. (
  • Ebralidze A, Wang Y, Petkova V, Ebralidse K, Junghans RP. RNA leaching of transcription factors disrupts transcription in myotonic dystrophy. Science. 2004 Jan 16;303(5656):383-7. Epub 2003 Dec 4. (
  • Finsterer J. Myotonic dystrophy type 2. Eur J Neurol. 2002 Sep;9(5):441-7. Review. (
  • Gene Review: Myotonic Dystrophy Type 1 (
  • Gene Review: Myotonic Dystrophy Type 2 (
  • Liquori CL, Ricker K, Moseley ML, Jacobsen JF, Kress W, Naylor SL, Day JW, Ranum LP. Myotonic dystrophy type 2 caused by a CCTG expansion in intron 1 of ZNF9. Science. 2001 Aug 3;293(5531):864-7. (
  • Machuca-Tzili L, Brook D, Hilton-Jones D. Clinical and molecular aspects of the myotonic dystrophies: a review. Muscle Nerve. 2005 Jul;32(1):1-18. Review. (
  • Meola G, Moxley RT 3rd. Myotonic dystrophy type 2 and related myotonic disorders. J Neurol. 2004 Oct;251(10):1173-82. Review. (
  • Ranum LP, Day JW. Myotonic dystrophy: RNA pathogenesis comes into focus. Am J Hum Genet. 2004 May;74(5):793-804. Epub 2004 Apr 2. Review. (
  • Udd B, Meola G, Krahe R, Thornton C, Ranum LP, Bassez G, Kress W, Schoser B, Moxley R. 140th ENMC International Workshop: Myotonic Dystrophy DM2/PROMM and other myotonic dystrophies with guidelines on management. Neuromuscul Disord. 2006 Jun;16(6):403-13. Epub 2006 May 8. (
  • Wheeler TM, Thornton CA. Myotonic dystrophy: RNA-mediated muscle disease. Curr Opin Neurol. 2007 Oct;20(5):572-6. Review. (


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? ( in the Handbook.

Reviewed: November 2010
Published: February 1, 2016