What is Myotonic Dystrophy?

Myotonic dystrophy is an inherited disorder of the muscles and other body systems. This is the most common form of muscular dystrophy in adults.

These disorders are characterized by progressive muscle wasting and weakness, especially in the lower legs, hands, neck and face. People with myotonic dystrophy often have prolonged muscle contractions (myotonia) and are unable to relax certain muscles after use. For example, a person may be incapable of releasing a grip on a doorknob or handle.

Other signs and symptoms of myotonic dystrophy may include clouding of the lens of the eye (cataracts), cardiac abnormalities, hair loss and inability to conceive a child (infertility). The characteristics of this disorder can occur at any age but usually develop for twenty years a person or paint. A variation called congenital myotonic dystrophy, can be noticed at birth. The severity of these signs and symptoms varies widely among affected individuals, even among members of one family. In general, the clinical features of myotonic dystrophy type 2 tend to be milder than those of type 1.

How common is myotonic dystrophy?
Myotonic dystrophy affects about 1 in 10,000 people worldwide. Approximately 98% of people with myotonic dystrophy have type 1. Otherwise, 2 p. 100 were type 2.

What genes are related to myotonic dystrophy?
Myotonic dystrophy caused by mutations in the DMPK gene and ZNF9.

The two forms of myotonic dystrophy, type 1 and type 2, have similar clinical features but are caused by mutations in different genes (DMPK and ZNF9). The mutation that causes myotonic dystrophy is a segment of DNA that is abnormally repeated in the DMPK gene or ZNF9. Rehearsals are a volatile region of the gene. Researchers believe that the large number of repetitions prevents cells in muscles and other tissues to function normally, leading to signs and symptoms of myotonic dystrophy.

How do people inherit myotonic dystrophy?
Myotonic dystrophy is inherited in an autosomal dominant aspect, which means a copy of the altered gene in each cell is sufficient to cause disease. In most cases, an affected person has one affected parent.

Type 1 myotonic dystrophy is passed from one generation to another, the disorder generally begins earlier in life and signs and symptoms become more severe. This phenomenon is called anticipation. In myotonic dystrophy type 1, anticipation is caused by an increase in the length of the unstable region of the DMPK gene. In myotonic dystrophy type 2, a more unstable region in the gene ZNF9 does not appear to influence age of onset of the disease.

What other names people use for myotonic dystrophy?
Myotonic dystrophy, myotonia atrophic myotonia dystrophica.

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