Kids Health Info

Duchenne muscular dystrophy DMD - information for carriers

  • Duchenne muscular dystrophy (DMD) is the most common childhood muscular dystrophy, affecting one in 5,000 boys.  Two-thirds of cases of DMD are inherited from mothers who carry changes, or mutations, in the dystrophin gene, the gene that causes DMD.  Females with mutations in the dystrophin gene are known as “carriers” and can pass the condition on to their children. Changes in the dystrophin gene can cause a variety of symptoms in female carriers. Some women have isolated elevation of the serum creatine kinase levels (or CK, a muscle enzyme that leaks into the blood from damaged muscles) without experiencing any symptoms; while others experience muscle cramps or symptoms of more severe muscle weakness more like DMD. Carrier females are also at risk of developing cardiomyopathy (disease of the heart muscle). 

    Signs and symptoms

    Female carriers with DMD mutations are usually asymptomatic (i.e. they show no symptoms of the condition themselves).  However, some will experience symptoms ranging from muscle pain and cramps with physical exertion, to weakness of the muscles in the limbs. Female relatives of patients with DMD should be offered appropriate genetic counselling and testing to determine whether or not they themselves are carriers. Female carriers of DMD mutations should have regular check-ups for development of cardiomyopathy.

    While most female carriers of DMD mutations do not have symptoms, as many as one in five will experience some symptoms.  Symptoms may occur as early as the first decade of life, or may develop much later in life. The symptoms range from muscle pain and cramps with physical exertion, to severe muscle weakness.  Heart problems are usually mild and limited to changes that are noted during tests such as electrocardiogram (ECG) or echocardiogram (echo).  About 10 per cent of carriers have dilatation (expansion) of the heart that appears on an echocardiogram. Only 40 per cent of carriers aged 18-60 years have completely normal heart function. 

    Diagnosis

    Adult females closely related to males with DMD (such as sisters, mothers and aunts), and first-degree relatives of known or possible female carriers, should have genetic counselling and testing for mutations to the dystrophin gene. Testing of carrier status is not routinely offered to children, as they do not yet have the maturity to give their informed consent to the test. However, you can begin talking to your daughter about the need for testing and the consequences of being found to be a carrier from mid-late adolescence. Female carriers without any symptoms should consider having cardiac testing prior to becoming pregnant, or when a pregnancy is discovered. Female carriers with abnormalities in their heart function should be referred to and managed by a cardiologist (a doctor who specialises in diseases of the heart).  

    When the genetic mutation of a boy with DMD is known, his treating doctor can generally request a DNA test for this mutation for close female relatives who may be potential carriers. If the affected boy is not available for testing and the gene mutation is not known, testing may still be possible if a DNA sample has been stored previously. 

    Management

    1.  For girls who are closely related to boys with DMD, education should be started in mid-late adolescence regarding the risk of developing cardiomyopathy, and the signs and symptoms of heart disease.
    2. Females at risk of being a carrier of the DMD mutation should see a cardiologist who has experience in the treatment of heart failure and/or neuromuscular disorders for a complete evaluation.  This should be done when their male relative is first diagnosed, after the age of 16 years if they are younger, or if there are any signs or symptoms of heart disease.  This evaluation should be done in all at-risk females, regardless of whether their carrier status has been tested or confirmed.
    3. All carriers of a DMD mutation should undergo an ECG and echocardiogram when their male relative is first diagnosed, or after the age of 16 years; and at least every three to five years after that. For patients who show abnormalities on these tests, a family history of heart disease and/or lifestyle risk factors (e.g. smoking, obesity) will be taken, and the cardiologist may recommend more frequent monitoring.
    4. Treatment of cardiac disease is similar to that for boys with DMD. 

    Key points to remember 

    • Female carriers of DMD mutations do not usually have symptoms.
    • Carriers who begin to experience symptoms can notice muscle pain and cramps with physical exertion, severe muscle weakness and/or dilatation of the heart.
    • Female relatives of patients with DMD should have their carrier status tested.
    • All at-risk females, regardless of their carrier status, should be monitored for development of cardiomyopathy. 

    More information 

    • RCH Neuromuscular Nurse Coordinator T: (03) 9345 4633
    • Muscular Dystrophy Australia www.mda.org.au T: (03) 9320 9555
    • TREAT-NMD Neuromuscular Network www.treat-nmd.eu

    Individual information 


    Name of your family doctor: _________________________________________ 


    Tel: _____________________________________________________________





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Disclaimer
This information is intended to support, not replace, discussion with your doctor or healthcare professionals. The authors of these consumer health information handouts have made a considerable effort to ensure the information is accurate, up to date and easy to understand. The Royal Children's Hospital, Melbourne accepts no responsibility for any inaccuracies, information perceived as misleading, or the success of any treatment regimen detailed in these handouts. Information contained in the handouts is updated regularly and therefore you should always check you are referring to the most recent version of the handout. The onus is on you, the user, to ensure that you have downloaded the most up-to-date version of a consumer health information handout.