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Myotonic dystrophy type 2


Other Names for this Disease
  • DM2
  • Dystrophia myotonica type 2
  • Myotonic myopathy, proximal
  • PROMM
  • Proximal myotonic myopathy
More Names
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Your Question

My husband has been diagnosed with type 2 myotonic dystrophy. We have two daughters who will be tested. Where can we learn more about this condition? 

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is myotonic dystrophy type 2?

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.
Last updated: 2/10/2014

What are the signs and symptoms of myotonic dystrophy type 2?

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]
Last updated: 2/10/2014

What causes myotonic dystrophy type 2?

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]
Last updated: 2/10/2014

How is myotonic dystrophy type 2 inherited?

Myotonic dystrophy type 2 is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is enough to cause symptoms of the condition. In most cases, an affected person has one affected parent.

As myotonic dystrophy is passed from one generation to the next, it generally begins earlier in life and signs and symptoms become more severe. This phenomenon is called anticipation. The cause of the anticipation in families with myotonic dystrophy type 2 is unknown.[2][3]
Last updated: 2/10/2014

How is myotonic dystrophy type 2 diagnosed?

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."
Last updated: 3/2/2010

How might myotonic dystrophy type 2 be treated?

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:

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.[4]

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.[4]

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

Last updated: 2/11/2014

Who can I contact to learn more about type 2 myotonic dystrophy?

The National Institute of Neurological Disorders and Stroke (NINDS), part of the National Institutes of Health (NIH), provides the following information page on muscular dystrophies which includes information about myotonic dystrophy.
http://www.ninds.nih.gov/disorders/md/md.htm

You can also contact NINDS directly for information on type 2 myotonic dystrophy.

NIH Neurological Institute
PO Box 5801
Bethesda, MD 20824
Toll free: 800-352-9424
Web site: http://www.ninds.nih.gov/

The Muscular Dystrophy Association (MDA) provides medical services for its members through MDA clinics across the country. These clinics serve people with a range of neuromuscular disorders, including type 2 myotonic dystrophy. Patients can receive medical care at a discounted cost for genetic disorders through the MDA clinics. To learn about accessing these services, contact the MDA.

Muscular Dystrophy Association (MDA) - USA
National Headquarters
3300 E. Sunrise Drive
Tucson, AZ 85718
Toll-free: 800-344-4863
Email: mda@mdausa.org  
Web site: http://www.mdausa.org
MDA pages on type 2 myotonic dystrophy:
http://www.mda.org/publications/fa-md-9.html
http://www.mda.org/publications/fa-mmd-qa.html

International Myotonic Dystrophy Organization
PO Box 1121
Sunland, CA 91041-1121
Toll-free: (866) 679-7954 (in the USA and Canada)
Phone: (818) 951-2311
Email: info@myotonicdystrophy.org
Web: http://www.myotonicdystrophy.org  
Last updated: 10/24/2008

References