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Myotonic Dystrophy
Wednesday, 13 July 2005
Wednesday, 13 July 2005
Myotonic Dystrophy Type 1, DM1, Steinert Disease

What

Myotonic Dystrophy (MD) is a rare multisystem genetic disorder primarily affecting muscle, but also affecting the heart, eye, brain and other body systems. The word “myotonic” means that muscles contract but can’t relax normally, therefore, the muscles become weak and waste away. Depending on the age of onset, the degree of severity is variable and the symptoms may be different in each person.

Who

Myotonic Dystrophy overall is the most common form of muscular dystrophy among Caucasians. There are 3 forms of the disorder – 1) congenital (present at birth), 2) classical childhood onset, and 3) mild adult onset. The congenital form is very rare, having an incidence of 1 in 100,000. The congenital form occurs in infants born to mothers with MD, but the mother may not have recognizable symptoms and may not even know she has this disorder before she has a child (ie, she may have the mild adult onset form). The classical form with its onset in childhood has an incidence of 1 in 8,000. The congenital form is thought to be more severe than developing the disorder during childhood.

Signs and Symptoms

Congenital: Children with congenital MD may present even before birth with decreased fetal movement and excess amniotic fluid. At birth, they may have reduced muscle tone and an expressionless face. Some children may have difficulties eating and breathing, and the ventricles in their brains may be enlarged. On examination, a “tented mouth” (upper lip somewhat raised and a drooping lower lip), and skeletal problems (eg, thin ribs and clubfeet) may become apparent. Later in childhood, children may have marked facial and jaw muscle weakness, progressive general muscle weakness, myotonia (when the muscle contracts, but does not relax normally and stays contracted), and delayed developmental progression including learning disabilities. Approximately 50-60% of affected children will be mentally retarded. Serious problems in the child’s heart rhythms may also develop as early as age 20. Classical: A child who develops MD during childhood will have normal development in the first years, but may have some clumsiness and speech problems. Usually during the school age years, problems with speech and hearing, poor coordination, learning difficulties, and cognitive problems become apparent. Also common are gastrointestinal problems, difficulty swallowing, bladder problems (eg, urgency to urinate), and chronic fatigue with tiredness. Eye problems (cataracts) may develop and also a decrease in attention and concentration in may be noticed by teachers and parents. Later during adolescence, serious problems in the heart rhythms may develop. Almost all affected persons have some degree of myotonia and muscle weakness due to atrophy or shrinkage of the muscles. Myotonia is most evident in the hands, and results in difficulty releasing grip and a feeling of muscle stiffness.

Possible Causes

Myotonic Dystrophy is an autosomal dominant genetic disorder. In MD there is an abnormality present on chromosome 19. Instead of a normal “CTG” pattern on the chromosome, people with MD have an increased number of this sequence, called a CTG Repeat Expansion. Because the CTG pattern is repeated too many times, the protein made by the gene does not function normally. The exact function of the DMPK gene and protein is still not known. Myotonic Dystrophy is also an example of what is called “genetic anticipation”, meaning that the child of a parent who has MD will have even more copies of the CTG sequence on chromosome 19 than the parent did. Therefore, the MD in the child will have an earlier onset and will likely be more severe. This pattern will continue through the family tree, showing a more severe form of the disease and earlier onset with each generation that is affected.

Diagnosis

If the congenital form of MD is suspected, a physical examination of the mother may be done since these children are usually born to affected mothers. The physician will likely take a family history to determine if the disorder is present in other family members, as well as examine the child to see if the signs and symptoms described above are present. A genetic test for the affected gene is available and very accurate. If that test is normal, however, or if another muscle disease is suspected, a muscle biopsy or EMG (electromyogram) may be done to see if the muscles look normal and function properly. In addition, prenatal testing by amniocentesis or fetal blood testing is available.

Treatment

No specific treatment exists for MD, but various forms of therapy can help alleviate symptoms. Infants with the congenital form often need help breathing and may use a ventilator in the early stages of the disease. If the infant has major difficulty feeding (common during the first two years of life), a tube may be inserted into the stomach to provide nutrition. Children with clubfeet will need to be examined by an orthopedic physician. A cardiologist should be involved and follow children for heart problems. Children who develop cataracts will need surgery to remove them. Those with learning difficulties may need special assistance in school. Children with speech and hearing difficulties may need to be evaluated by a speech pathologist. A physical therapist and occupational therapist should evaluate children with muscular weakness and provide any needed orthotics or assistance devices. While there is currently no known cure for MD, research is being done to determine the exact mechanism of the disorder in hope of finding the cure.

Prognosis

Children who are severely affected with the congenital form of MD are likely to have some limitations of physical function and may have mental problems as well. After the neonatal period (first 28 days of life), MD is rarely fatal early in life. The sooner the infant is breathing without a ventilator, the better prognosis the child has for the future. Congenitally affected infants improve in muscle weakness in the first years of life and most will learn to walk, although clubfeet and other skeletal problems may make this more difficult. Muscle problems become apparent during school age and speech development is delayed, but most children eventually learn to speak and care for themselves. Heart and other serious problems are prominent during puberty and are the most common causes of death. The childhood-onset form is not as severe as the congenital form, but cognitive problems are still present. Although symptoms are apparent later for the childhood-onset form, a similar outcome is eventually expected. With proper care, most children with MD who overcome neonatal difficulties can live to become adults.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

www.Myotonic.org
This is a great website that has links to current research, an online chat room, and a place where you can “ask the expert” about specific questions regarding your child’s condition or Myotonic Dystrophy in general.

Muscular Dystrophy Campaign Fact sheet on Myotonic Dystrophy This is a good website with educational information concerning this disorder.

Myotonic Dystrophy Support Group
This is a great website that offers lots of different types of support, a newsletter, and a tutorial to explain the genetic basis of the disorder.

A PDF Booklet from the University of Washington titled: Myotonic Dystrophy: Making an Informed Choice About Genetic Testing
Well written and thoughtful information about myotonic dystrophy and genetic testing.

Google Search for Myotonic Dystrophy

References and Sources

www.utdol.com/application/topic/topicText.asp?file=ped neur/22284&type=P&selectedTitle=1~11 Harper PS, van Engelen BGM, Eymard B, Wilcox, DE (2003). Myotonic Dystrophy: present management, future therapy. New York: Oxford University Press Inc. Karpati G, Hilton-Jones D, Griggs RC (2001). Disorders of Voluntary Muscle. 7th ed. New York: Cambridge University Press.