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Inherited Disorders and Birth Defects

Myotonic Dystrophy

01/09/2009

Question:

My dad had Myotonic Dystrophy. His medical doctor told me. He also told me that it does not happen to girls and that it also does not skip a generation. I have muscle aches but I seem better now that I have retired and gotten out of the stress filled and cold computer room. I have 2 sons, 41 and 35. The oldest has a lot of muscle or joint problems. He works every day but I now have this disease on my mind and would love to have accurate info concerning it. What test is done to determine it? I just saw in the paper that someone died at the age of 55 due to this. Now I am really curious. Thanks.

Answer:

If the diagnosis of myotonic dystrophy is correct in your father, then girls can also be affected.

Myotonic dystrophy (DM) affects multiple body systems including skeletal muscle and smooth muscle, as well as the eye, heart, endocrine system, and central nervous system. Symptoms can be from mild to severe.

DM is often put into 3 categories: mild, classical, and congenital. Mild DM usually has cataracts and mild myotonia. Myotonia is difficulty relaxing the muscles after they contract. Life span is normal. Classical DM has muscle weakness and wasting (loss of muscle), myotonia, cataracts, and often heart conduction problems (problems with the electrical system of the heart). Adults with classical DM may become physically disabled and may have a shortened life span. The congenital type of DM is noticed at birth and has hypotonia (decreased muscle tone) and severe generalized weakness. These infants often have breathing problems and may die young.

Myotonic dystrophy is due to a genetic change (mutation) in the myotonin protein kinase gene (DMPK). There is gene testing available for DM.

DM is inherited in an autosomal dominant manner. Since our chromosomes come in pairs, we have two copies of the myotonin protein kinase gene. A person with DM has a genetic change in one of their two copies of this gene. Only one copy of the gene with the genetic change is necessary to cause DM. Any person - girl or boy - with the gene for DM has a 50% chance of passing the gene on to any of their children. If the child inherits the gene for DM they will be affected. That also means that there is a 50% chance that any child will not inherit the mutation that causes DM.

There can be lots of different reasons for having muscle and joint problems. If you are concerned about the possibility of either you or your son having myotonic dystrophy, then I would recommend you talk to a geneticist or genetic counselor to discuss this concern. You can find a genetics center near you by contacting the National Society of Genetic Counselors resource web site below.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University