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Disease Profile

Myotonic dystrophy type 2

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

Adult

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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.

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 type 2; DM2; Proximal myotonic myopathy;

Categories

Congenital and Genetic Diseases; Endocrine Diseases; Eye diseases;

Summary

Myotonic dystrophy type 2, one of the two types of myotonic dystrophy, is an inherited muscular dystrophy that affects the muscles and other body systems (e.g., heart, eyes, and pancreas). It is characterized by prolonged muscle tensing (myotonia) as well as muscle weakness, pain, and stiffness. Signs and symptoms usually develop during a person's twenties or thirties. Muscles in the neck, fingers, elbows, and hips are typically affected; facial and ankle muscles are less commonly involved.[1] The severity of myotonic dystrophy type 2 varies widely among affected people, even among family members.[2] It is inherited in an autosomal dominant pattern and is caused by mutations in the CNBP gene.[2] Treatment is based on each person's specific signs and symptoms.

Symptoms

Myotonic dystrophy type 2 is characterized by progressive muscle wasting and weakness. Symptoms typically begin in a person's twenties. People with this condition 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; temporary locking of their jaw; and muscle pain and weakness that mainly affects the neck, shoulders, elbows, and hips. Less common symptoms include abnormalities of the electrical signals that control the heartbeat (cardiac conduction defects); clouding of the lens in the eyes (cataracts); and diabetes. Males may experience balding and infertility. The severity of symptoms varies among affected people. Compared to myotonic dystrophy type 1, type 2 is milder and does not necessarily shorten a person's lifespan.[3][1]

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:
HPO ID
80%-99% of people have these symptoms
Cataract
Clouding of the lens of the eye
Cloudy lens

[ more ]

0000518
Myotonia
0002486
Percent of people who have these symptoms is not available through HPO
Autosomal dominant inheritance
0000006
Decreased circulating IgG level
0004315
Decreased circulating total IgM
0002850
Diabetes mellitus
0000819
Elevated circulating follicle stimulating hormone level
0008232
Elevated serum creatine kinase
Elevated blood creatine phosphokinase
Elevated circulating creatine phosphokinase
Elevated creatine kinase
Elevated serum CPK
Elevated serum creatine phosphokinase
High serum creatine kinase
Increased CPK
Increased creatine kinase
Increased creatine phosphokinase
Increased serum CK
Increased serum creatine kinase
Increased serum creatine phosphokinase

[ more ]

0003236
Frontal balding
0002292
Hypogonadism
Decreased activity of gonads
0000135
Insulin insensitivity
0008189
Iridescent posterior subcapsular cataract
0007889
Myalgia
Muscle ache
Muscle pain

[ more ]

0003326
Neck flexor weakness
Neck flexion weakness
0003722
Oligospermia
Low sperm count
0000798
Palpitations
Missed heart beat
Skipped heart beat

[ more ]

0001962
Proximal muscle weakness
Weakness in muscles of upper arms and upper legs
0003701
Tachycardia
Fast heart rate
Heart racing
Racing heart

[ more ]

0001649
Type 2 muscle fiber atrophy
0003554

Cause

Mutations in the CNBP gene cause myotonic dystrophy type 2. The exact function of this gene is not known. The protein made by the CNBP gene is mainly found in the heart and in skeletal muscles, where it probably helps regulate the function of other genes.[3]

In people with myotonic dystrophy type 2, a short piece of DNA is abnormally repeated many times, forming an unstable area of the gene. 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.[2][3]

Diagnosis

Myotonic dystrophy is diagnosed by doing a physical exam. A physical exam can identify the typical pattern of muscle wasting and weakness and the presence of myotonia. A person with myotonic dystrophy may have a characteristic facial appearance of wasting and weakness of the jaw and neck muscles. Men may have frontal balding.[2]

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 muscle electrical discharge.[2] The definitive test for myotonic dystrophy type 2 is a genetic test. For this test, certain cells within the blood are analyzed to identify a change (mutation) in the CNBP gene. [2]

The University of Washington provides more information on genetic testing for myotonic dystrophy type 2 in their publication titled, "Myotonic Dystrophy: Making an Informed Choice About Genetic Testing."

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.
  • Orphanet lists international laboratories offering diagnostic testing for this condition.

    Treatment

    There is currently no treatment available to stop or slow the progression of myotonic dystrophy type 2. Management options depend on the symptoms that each affected person has, and aim to treat each specific symptom. For example:[1]

    • Ankle-foot braces, wheelchairs, or other assistive devices may be used as needed for weakness
    • Defibrillator placement may be needed for arrhythmias
    • Cataracts can be removed for those with impaired vision
    • Testosterone replacement therapy may be useful for hypogonadism in males

    Myotonia is usually mild and rarely requires treatment. Routine exercise appears to help with pain control, as well as with muscle strength and endurance. The effectiveness of most medications for pain management varies. Mexilitene, which is very effective for some forms of myotonia, has helped control muscle pain in some people with this condition. Other medications that have been used with some success include gabapentin, nonsteroidal anti-inflammatory drugs (NSAIDS), low-dose thyroid replacement, low-dose steroids, and tricyclic antidepressants. Cholesterol-lowering medications should be avoided when they are associated with increased weakness.[1]

    There are steps a person can take to prevent some secondary complications. Anesthetic risk may be increased, so careful assessment of heart and respiratory function before and after surgery are recommended. Affected people should also have a yearly electrocardiogram or cardiac MRI to detect possible conduction defects or cardiomyopathy.[1]

    You can see more detailed information about the management of myotonic dystrophy type 2 on the GeneReviews Web site.

    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

        • Genetics Home Reference (GHR) contains information on Myotonic dystrophy type 2. This website is maintained by the National Library of Medicine.
        • The Muscular Dystrophy Association (MDA) provides additional information about myotonic dystrophy. Click on the link to view this information.
        • Myotonic Dystrophy Foundation provides additional information about Myotonic dystrophy type 2.
        • The National Human Genome Research Institute's (NHGRI) website has an information page on this topic. NHGRI is part of the National Institutes of Health and supports research on the structure and function of the human genome and its role in health and disease.
        • 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.
          • 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.
          • 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. 
          • 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 type 2. Click on the link to view a sample search on this topic.

            Selected Full-Text Journal Articles

              References

              1. Dalton JC, Ranum LPW, and Day JW. Myotonic Dystrophy Type 2. GeneReviews. July 3, 2013; https://www.ncbi.nlm.nih.gov/books/NBK1466/.
              2. Learning About Myotonic Dystrophy. National Human Genome Research Institute (NHGRI). June 4, 2012; https://www.genome.gov/25521207. Accessed 4/22/2015.
              3. Myotonic dystrophy. Genetics Home Reference (GHR). November 2010; https://ghr.nlm.nih.gov/condition=myotonicdystrophy. Accessed 5/11/2011.
              4. Myotonic muscular dystrophy. Muscular Dystrophy Association. https://mda.org/disease/myotonic-muscular-dystrophy/overview. Accessed 2/10/2014.
              5. Françoise Bouhour. Proximal Myotonic Myopathy. Orphanet. July, 2007; https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=606. Accessed 2/10/2014.
              6. David A Chad and Basil T Darras. Myotonic dystrophy: Prognosis and management. UpToDate. Waltham, MA: UpToDate; January, 2014; Accessed 2/10/2014.

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