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Monday, May 20, 2013
Inherited Disorders and Birth Defects
Should I be screened for myotonic dystrophy
Of my grandmother’s children: 1st My mother died at 54 of vascular problems; 2nd a son died at 9 months, diagnosed with myotonic dystrophy; 3rd son diagnosed with myotonic dystrophy, died at 38; 4th daughter diagnosed with myotonic dystrophy, died at 49; 5th son diagnosed with myotonic dystrophy, died at 51. My grandmother developed symptoms of myotonic dystrophy in her early 40s, was bed-ridden by 50, and died aged 58.
Although my mother was never told she had symptoms of MD, could the fact she died so young be linked? Should I be screened for myotonic dystrophy?
As you know from your family history, myotonic dystrophy (MD) 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.
MD is often put into 3 categories: mild, classical, and congenital. People with mild MD often have cataracts and mild myotonia (difficulty relaxing the muscles after contraction). People with classical MD have muscle weakness and loss of muscle, myotonia, and often have heart problems (problems with the electrical system of the heart). Adults with classical MD often become physically disabled and have a shortened life span. The congenital type usually has severe weakness at birth. These babies often have breathing problems and may die in infancy.
Myotonic dystrophy is due to a genetic change (mutation) in the myotonin protein kinase gene (DMPK). This abnormality in the DMPK gene results in what is called an expansion of the CTG trinucleotide repeat. If the CTG repeat length becomes larger than 37 repeats, it is abnormal. There is genetic testing for MD, but usually you need to test someone who is affected first to know where to look in people who are not affected.
MD is inherited in an autosomal dominant manner. People with MD have a genetic change or alteration in one of their two copies of this gene. Only one copy of the gene with the genetic alteration is necessary to cause MD. Any person with the mutation (gene change) for MD has a 50% chance of passing the gene on to any of their children. If the child inherits the gene for MD they will be affected. Any person who does not inherit the mutation for MD will not be affected.
In your family, it would appear that your grandmother passed the mutation on to many of her children. However, if your mother did not inherit the mutation that causes MD, then you are not at risk to have MD. The important question is whether or not your mother had very mild symptoms of MD and the diagnosis was missed. People with MD often have heart problems, but it is not possible to say whether your mother's vascular problems are related to the MD running in the family without more information.
These are excellent questions and it may be appropriate for you to have testing. I would highly recommend that you talk to a geneticist or genetic counselor to discuss all the current information and testing available. You can find a genetics center near you by contacting the National Society of Genetic Counselors resource web site below.
Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University