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Muscular dystrophy refers to a group of genetic (inherited) conditions that cause progressive deterioration of the body's muscles, with increasing weakness and disability.
Duchenne muscular dystrophy (DMD) is caused by a defect in a gene inherited on the X chromosome. Since males have only one X chromosome, DMD primarily affects boys. Women can carry the defective gene but usually will not show symptoms since they have a normal copy of the gene on their second X chromosome. In Duchenne muscular dystrophy, the defect in the dystrophin gene causes muscles to produce abnormally low levels of the dystrophin muscle protein so that the membranes around muscle cells become weak and tear easily, eventually leading to death of muscle fibres and replacement by scar tissue. DMD is the most common form of muscular dystrophy, occurring in one out of every 3,000 male newborns.
Becker-type muscular dystrophy is also due to mutations in the dystrophin gene on the X chromosome, and occurs in males. However the defects in the gene result in a less severe deficiency of the dystrophin protein so that the onset of muscle weakness is usually later in onset and milder compared to DMD.
Myotonic dystrophy can occur in both sexes and is the most common form of adult muscular dystrophy, with symptoms often starting in adolescence. Stiffness of the muscles (myotonia) often occurs before muscle weakness. It is inherited in an autosomal dominant fashion, which means that an affected person has a one in two chance of passing th disorder on to each of their offspring.
Limb-girdle muscular dystrophy describes a large mixed group of different forms of muscular dystrophy with weakness predominant affecting the muscles of the shoulders and hips. It can effect both males and females, and may be inherited in a dominant or recessive fashion.
Facioscapulohumeral muscular dystrophy also occurs in both sexes. It is inherited in an autosomal dominant fashion, which means that an affected person has a one in two chance of passing the disorder on to each of their offspring.. However, because the symptoms vary in intensity, family members may have such mild forms of the illness that they are unaware of any muscle problems. Weakness of the facial muscles and the shoulder are typical.
Emery-Dreifuss, Oculopharyngeal, Distal and Congenital Muscular Dystrophy are other forms of the disorder. (For information on these see www.mdausa.org/disease/).
In Duchenne muscular dystrophy (DMD) symptoms usually begin in the child between ages 2 and 4. Because of a progressive weakening of leg muscles, the child falls frequently and has difficulty getting up from the ground and also has trouble running, walking or running normally. The calf muscles may be relatively large. Weakness is progressive. By the age of 12, most patients are unable to walk and need to use a wheelchair. Other muscle groups become affected resulting in abnormal curvature of the spine (scoliosis), and progressive weakness of the muscle of breathing resulting in respiratory failure. In addition, some patients with DMD have mild intellectual delay and heart problems (cardiomyopathy) due to lack of the dystrophin protein in the brain and in the heart muscle.
In Becker-type muscular dystrophy symptoms are similar to those of DMD but are milder and tend to begin later. The muscle weakness is progressive and there is variable involvement of the heart and muscles of breathing.
Myotonic dystrophy is associated with muscle stiffness due to difficulties in muscle relaxation as well as muscle weakness. The symptoms can begin at any time – from birth to adulthood. The clinical severity of the muscle stiffness and weakness tends to increase in each subsequent generation. Of note, a mildly affected mother can have a very severely affected baby who is very weak from birth and may have problems with respiratory failure as well as intellectual impairment. In addition to the skeletal muscle symptoms, patients with myotonic dystrophy may have problems with their heart rhythm (called conduction block) so that regular heart checks are mandatory to monitor for cardiac arrhythmia. Some patients may also develop diabetes and cataracts. Deterioration of the tongue and throat muscles may cause speech problems and difficulty swallowing, and there may be breathing problems.
In limb-girdle muscular dystrophy symptoms begin at any time from childhood or early adulthood. Progressive muscle weakness affects predominantly the shoulders and hips, together with breathing problems (if the diaphragm is involved). Involvement of the heart muscle is present in some patients, and there may be heart failure or abnormal heart rhythms.
The symptoms of facioscapulohumeral muscular dystrophy may begin during infancy, late childhood or early adulthood. Usually, the first sign is facial weakness, with difficulty smiling, whistling and closing the eyes. Later, there is difficulty raising the arms or flexing the wrists and/or ankles.
Currently, there is no cure for muscular dystrophy and no way to stop its progression. In general, patients are given supportive care, such as occupational and physical therapy to maximize their ability to function in daily life. Stretching limbs to avoid tightened tendons and muscles is particularly important — when tightness of tendons develops surgery can be performed. It is very important to monitor the function of the respiratory muscles on regular basis, as some patients may require assistance with their breathing. Similarly, the heart may need to be checked by a cardiologist on a regular basis to detect early signs of cardiac dysfunction.
In addition, people with muscular dystrophy are given age-appropriate dietary therapy to help them follow a healthy meal plan while avoiding obesity. Obesity is especially harmful to patients with muscular dystrophy because it places additional strain on their already weak muscles. In boys with Duchenne muscular dystrophy, corticosteroids may be prescribed to delay progression of the weakness temporarily, and delay loss of the ability to walk. However, some patients cannot tolerate this medication because of side effects.
Other experimental treatments are being developed, including gene therapy, and myoblast-transfer therapy.However it is still not possible to deliver healthy replacement genes and muscle cells efficiently to the millions of cells it would take to reverse muscle weakness. Thus these therapies are not likely to be an available for many years,
Most forms of muscular dystrophy are chronic and progressive and persist throughout life. Early death may result from severe involvement of respiratory or cardiac muscles.
Further Information and Support
My Doctor (for contact details of Australian Support Associations)
Better Health Channel
Muscular Dystrophy Association - USA
National Institute of Neurological Diseases and Stroke - USA
Worldwide Education and Awareness for Movement Disorders (WE MOVE) - USA
Reviewed by Professor Kathryn North, MD, FRACP, Professor, Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney and Head, Neurogenetics Research Unit, The Children's Hospital at Westmead, Australia