Myotonic Dystrophy

Myotonic Dystrophy is a disease that is genetically based and inherited from one generation to the next. One out of two of a person with myotonic dystrophy will most likely have symptoms of the disease. Unlike most diseases, the symptoms that a person with this disease varies from person to person. Some people are just mildly affected others are severely affected. This makes it hard to tell you exactly how the disease will affect a particular individual.

Myotonic dystrophy is a rare disease with an incidence of about one in 8000. The incidence of the congenital form is higher with an incidence of 1/100,000 That means that most doctors will not have a patient with the disease in their practice. Thus, many people are turning to organizations like the International Myotonic Dystrophy Organization (IMDO) for help and assistance.

Myotonic Dystrophy is generally classified into two types. One is extremely rare and we will not deal with that type in our pages. The other type can be subdivided into 4 distinct Types:

Congenital: Appears at birth and is most severe (not likely with DM2)
Juvenile: Appears after birth and in teen years
Adult: Appears in the late 20's to early 40's
Late Onset: Appears later after 40's and generally mild

As a general rule the earlier the disease is apparent or can be detected the more severe the symptoms will be. 

Myotonic Dystrophy is caused by an excessive number of CTG repeats on Chromosome 19. A "normal" number of Repeats is 5-38, Over 38 and myotonic dystrophy can occur. In the most severe congenital form the number of repeats is over 3,000. The disease has an effect called "anticipation" This means that the disease gets progressively worse with each generation. As a general rule 50% of the children will inherent the disease. It is particularly important that female members of the family in childbearing years be tested with a DNA test to find out if they have the disease. This can prevent the most severe from of the disease, the congenital form, from occurring. A new form of myotonic Dystrophy was discovered in August of 2001.

There are now two types of myotonic Dystrophy

DM1 is known as Type 1
DM2 is know as Type 2 also known as PROMM or "Proximal Myotonic Myopathia"

DM1 is caused by an expanded repeat of CTG on Chromosome 19
DM2 is caused by an expanded quadruplet repeat of CCTG on Chromosome 3

Differences in DM1 and DM2

DM2 does not seem to cause the severe congenital form when the mother that has the disease has an infant. Also the apathetic personality traits with DM1 do not seem to be associated with DM2. People with DM2 will have more weakness in the trunk of the body (proximal) versus DM1 will have more weakness in the distal parts of the body like legs and arms.

Myotonic Dystrophy is known as a multisystem disease. That means that the various types of tissue and organs are affected. Thus, the disease may affect the eyes, heart, and muscles. This is somewhat different than most diseases. Most disease will affect just one system. This basic mechanism of why different systems are affected is unknown. Recently a hypothesis that it is a small cellular component called Messenger RNA that might be the culprit. However it can be inferred that some type of biochemical mechanism or other mechanism that can have a more universal affect.

The disease causes a lot of unusual problems in people with the disease. They may have trouble staying awake and have low energy levels. They may have depression. There may be hair loss or digestive problems. It is very hard to relay to people that this is a real disease and that the problems are real and not just a result of lack of motivation. In fact, lack of motivation is one of the results of the disease.

You also might be accessing the site to find out if you have the disease. The definitive test for Myotonic Dystrophy is the a Chromosome test but the grip test will usually allow you a quick and easy way to know if an individual may be afflicted with Myotonic Dystrophy. Affected individuals will not be able to open and close their hand rapidly and will have a characteristic grip. View these images below to confirm diagnosis. (It may take about 1 minute to load these at 56K)

  Go to Grip Test Image      Go to Grip Test Release

This site concentrates on information on myotonic dystrophy. If you are looking for information on Myotonic Dystrophy, there is an excellent book called Myotonic Dystrophy it is by Peter S. Harper , it is over 300 pages exclusively devoted to in-depth information on Myotonic Dystrophy. The third edition is now available. You can order this book from the publisher. You may be able to obtain this book through an interlibrary loan from the local medical school. It is somewhat technical but a wealth of information on this subject. I would highly recommend this book.

Congenital Myotonic Dystrophy