Myotonic dystrophy type 1

What causes myotonic dystrophy type 1?

MD1 is caused by a mutation called a CTG trinucleotide repeat in the DMPK gene. It is made up of three DNA building blocks (CTG stands for cytosine, thymine, and guanine) that appear multiple times in a row. If the number of CTG repeats is more than 34, it creates an unstable region in the gene. Repeats between 35 and 49 are considered premutations. Individuals with CTG repeats in this range do not have symptoms themselves, but their children are at increased risk of inheriting a larger repeat size and thus having symptoms.

The protein made by the DMPK gene is believed to play a role in communication and impulse transmission within and between cells. It appears to be important for the correct functioning of cells in the heart, brain, and skeletal muscles. The more than normal number of CTG repeats leads to the creation of longer and toxic RNA. This causes problems for cells mainly because it traps and disables important proteins. This prevents cells in muscles and other tissues from functioning normally, leading to the signs and symptoms of MD1.

Last updated on 05-01-20

How is myotonic dystrophy type 1 inherited?

MD1 is inherited in an autosomal dominant pattern, which means one copy of the mutated gene in each cell is sufficient to cause the disorder. In most cases, the person with MD1 has a parent who also has the disorder. The children of a person with MD1 have a 50% chance of inheriting the disorder.

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 is called anticipation. It is caused by an increase in the length of the number of CTG repeats (unstable region) in the DMPK gene. The expansion of the unstable region causes the features of the disorder to become more severe with each successive generation.

Some people diagnosed with MD1 have a parent who has the signs and symptoms of the disorder; others do not. A parent may appear to be unaffected because symptoms may be mild or absent. Genetic testing is available to confirm the presence of the condition.

Last updated on 05-01-20

Does myotonic dystrophy cause fatigue?

Yes. Sleepiness and fatigue are common features of myotonic dystrophy type 1. Medications to reduce fatigue are available. We recommend that you dicuss your treatment options with a healthcare provider.

In addition, heart block is a common and potentially dangerous complication of myotonic dystrophy type 1, that can cause light headedness, dizzy spells, near fainting, and fainting. These symptoms should be reported to your doctor right away.

Last updated on 05-01-20

How might myotonic dystrophy type 1 associated vision problems be treated?

Treatment of eye and vision problems must be individually tailored. Refractive error and astigmatism can be corrected with eyeglasses, contact lenses, or surgery. Special glasses with eye "crutches" can be used to improve vision in people with ptosis. Surgery can be done to treat ptosis and cataracts, however ptosis often recurs and special precautions must be taken with anesthesia. If severe, strabismus may also be treated with surgery.

Last updated on 05-01-20

How does myotonic dystrophy type 1 affect vision?

Myotonic dystrophy type 1 is associated with an increased risk for a variety of vision and eye problems, including:

Last updated on 05-01-20

Name: Myotonic Dystrophy Foundation 1004-A O'Reilly Avenue
San Francisco, CA, 94129, United States
Phone: +1-415-800-7777 Toll Free: 1-86-MYOTONIC (1-866-968-6642) Email: Url:
Name: Muscular Dystrophy Association MDA 222 S Riverside Plaza Suite 1500
Chicago, IL, 60606, United States
Toll Free: 1-833-275-6321 (Helpline) Email: Url:
Name: Muscular Dystrophy UK 61A Great Suffolk Street
London, SE1 0BU, United Kingdom
Phone: (+44) 0 020 7803 4800 Toll Free: 0800 652 6352 (Helpline) Email: Url:
Name: Myotonic Dystrophy Support Group 19-21 Main Road Gedling
Nottingham NG4 3HQ
United Kingdom
Phone: 0808 169 1960 Email: Url:

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The RareGuru disease database is regularly updated using data generously provided by GARD, the United States Genetic and Rare Disease Information Center.

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