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Myotonic Muscular Dystrophy

Introduction

Here you'll find answers to some of the common questions that parents have about this condition, along with links to other relevant high quality web sites. More comprehensive information can be found in the Myotonic Muscular Dystrophy module in our Diagnoses & Conditions section. See Myotonic Muscular Dystrophy Type 1. These modules are written for primary care clinicians, but the information in them may also be valuable for parents and family members.

What is Myotonic Muscular Dystrophy and what causes it?

Myotonic muscular dystrophy (MMD) is an inherited muscle condition that cuase slowly progressive muscle weakness and wasting and associated symptoms. Children who are born with myotonic muscular dystrophy have the congenital form, and have a more severe form of the condition, often having swallowing and breathing problems at birth. Involved muscles are usually in the face, jaw and neck area. Muscle stiffness or 'myotonia' is characteristic, especially affecting the hands. Associated problems include:
  • cataracts
  • heart arrhthymias
  • learning problems
  • frontal balding
  • diabetes
Most MMD is caused by a mutation on chromosome 19 where an unstable area of the chromosome expands from a slight expansion in mildly affected individuals to a large one in severely affected children usually with the congenital form. There is another form of MMD, type 2, that is caused by an unstable area n chromosome 3. It is similar, but not the same as MMD type 1.

Myotonic muscular dystrophy is an inherited condition. This condition follows a 'dominant' inheritance pattern, which means that on average half of the children of an affected person are themselves affected. Both men and women are equally likely to be affected and to pass on the disorder, but affected women are more likely to have a severely affected child. If the disease is inherited through the mom, the disorder tends to be more severe in successive generations.

What are the symptoms?

Symptoms of the congenital (present at birth) form:
  • breathing problems
  • high arched palate
  • difficulty eating
  • muscle contractures
  • distinctive facial features due to facial muscle weakenss
  • myotonia which is present in older children and adults is not present in infants, although often it is possible to find myotonia in the infants mother
Symptoms of the child/adult onset form:
  • muscle weakness, especially face, neck, hands, giving the face a distinctive appearance
  • muscle contractures, especially heel cords
  • myotonia
  • frontal balding
  • diabetes
  • heart arrhthymias

How is myotonic muscular dystrophy diagnosed?

A gene test performed on a blood sample

What is the prognosis?

Children with the congenital form may have severe difficulties. Individuals with the later-onset form have very slowly progressive weakness. Due to abnormalities in swallowing muscles, choking may be a problem. Older individuals may have heart arrhthymias and should be periodicallly monitored by carditology and should do well with proper preventive care..

What is the risk for my family and future babies?

If you have suspicions that other children or adults in the family have myotonic dystrophy, they should be examined by a specialist.
If you have one child with myotonic muscular dystrophy, any future children carry a 50% risk of also having MMD. If the condition is inherited through the mom, a more severe form of MMD congenital MMD may occur in those future children.

What is the treatment?

There is no specific treatment for myotonic muscular dystrophy although specific symptoms such as drooling and fatigue may be treated symptomatically.

My son has been found to have myotonic dystrophy, and he is having a lot of learning problems at school. Could this be related, and should I tell the school?

Yes, you should certainly tell the school, as it will help them to know that he has a medical condition. Some of his problems may be due to poor speech from his face and jaw muscles being affected, daytime sleepiness or due to difficulties paying attention. Where the condition has been present from early childhood there can be true learning difficulties, and he may need psychological testing to see if this is the case or not. He may be eligible for a statement of special needs which would allow him to have assistance with his schooling. http://www.myotonicdystrophysupportgroup.org/

What is the difference between myotonic muscular dystrophy and muscular dystrophy?

Myotonic Dystrophy affects both sexes equally and can be passed on by both men and women. It is quite different in that respect from other muscular dystrophies, especially the Duchenne type, which only affects males but is passed on by healthy females. Any child of an affected person has a 50% risk of inheriting the disorder. If a family member is unaffected and shown to be free of it by full testing, it is most unlikely to be passed on by that person. http://www.myotonicdystrophysupportgroup.org/

When my child has a surgery, is anesthesia a risk?

Yes, even those who are mildly affected have a higher risk when they receive anesthesia. Your family doctor should be told and any surgeon and anesthetists who treats you. Leaflets on detailed precautions are available, as is a warning card to carry (from the Myotonic Dystrophy Support Group - see the services page). If an operation is really necessary, it should be carefully planned and done in a hospital with an intensive care unit, just in case. Most problems happen because doctors (and patients) are not aware of the possibility of a problem. The main problems are because the breathing muscles are weak and sensitive to anesthetics and drugs used after surgery, as well as disturbances of the heart rhythm.

Why does my child take so many naps and have to rest after just a few minutes at the playground?

For unclear reasons, children and adults with MMD fatigue very easily. Adults will describe having to take a nap after doing simple household tasks. Although there are several medications that might be helpful for fatigue in older children and adults, including stimulants and modafinil, these are rarely used in young children. Behavioral management should include keeping to set bedtimes, naptimes, and wakeup times, and planned rest periods during the day. Energy conservation is also important. The family should be encouraged to use a disability placard/plate for their car to preserve the child's energy.

My son is 10 years old and still drooling. Why is this, and is there anything we can do to stop it?

Children with congenital myotonic muscular dystrophy often have significant facial muscle weakness that may lead to drooling. Drooling can be a social barrier and will often respond to treatment. Your first step should be to consult a feeding specialist for a thorough evaluation of your son's oral abilities. Depending on results, there are several treatment options. The feeding specialist may be able to give your son strategies to alleviate drooling. If that is not successful, a visit to an otolaryngologist may be helpful for the consideration of temporary treatments to decrease drooling (botulinum toxin injections) or longer-lasting surgical treatment.

Who gets myotonic muscular dystrophy (MMD)?

Most children who are born with the congenital form of MMD inherit it from their mother, although in general myotonic dystrophy can be inherited from a mother or a father. It is one of the most common muscular dystrophies.

Authors

Author: Lynne M Kerr, MD, PhD - 3/2012
Compiled and edited by: URLEND Trainees, 2011-2012 - 3/2012

Funding/Support

The Medical Home Portal thanks the 2011-2012 URLEND Medical Home Portal trainees group for their contribution to this page.