Myotonic dystrophy type 2
Other Names for this Disease
- Dystrophia myotonica type 2
- Myotonic myopathy, proximal
- Proximal myotonic myopathy
What are the signs and symptoms of myotonic dystrophy type 2?
What causes myotonic dystrophy type 2?
How is myotonic dystrophy type 2 inherited?
How is myotonic dystrophy type 2 diagnosed?
How might myotonic dystrophy type 2 be treated?
What is the long-term outlook for people with myotonic dystrophy type 2?
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.
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.
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. 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. 
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."
- 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.
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.
You can see more detailed information about the management of myotonic dystrophy type 2 on the GeneReviews Web site.
The prognosis for affected people can depend on the extent of heart (cardiac) involvement. While definitive information is not available, it appears there is relatively little shortening of the lifespan in people with myotonic dystrophy type 2.
- Dalton JC, Ranum LPW, Day JW. Myotonic Dystrophy Type 2. GeneReviews. April 23, 2007; http://www.ncbi.nlm.nih.gov/books/NBK1466/. Accessed 4/8/2012.
- Learning About Myotonic Dystrophy. National Human Genome Research Institute (NHGRI). March 23, 2011; http://www.genome.gov/25521207. Accessed 4/8/2012.
- Myotonic dystrophy. Genetics Home Reference (GHR). November 2010; http://ghr.nlm.nih.gov/condition=myotonicdystrophy. Accessed 5/11/2011.
- Joline C Dalton, Laura PW Ranum, and John W Day. Myotonic Dystrophy Type 2. GeneReviews. July 3, 2013; http://www.ncbi.nlm.nih.gov/books/NBK1466/. Accessed 2/10/2014.
- Myotonic muscular dystrophy. Muscular Dystrophy Association. http://mda.org/disease/myotonic-muscular-dystrophy/overview. Accessed 2/10/2014.
- Françoise Bouhour. Proximal Myotonic Myopathy. Orphanet. July, 2007; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=606. Accessed 2/10/2014.
- David A Chad and Basil T Darras. Myotonic dystrophy: Prognosis and management. UpToDate. Waltham, MA: UpToDate; January, 2014; Accessed 2/10/2014.