A group of genetic conditions in which muscles become weak and wasted
- Present at birth
- Almost always affects boys
- Due to an abnormal gene
- Lifestyle is not a significant factor
The two main types of muscular dystrophy almost exclusively affect boys. The most common type is Duchenne muscular dystrophy, which affects about 1 in 3,500 boys in the UK and causes serious disability from early childhood. A second, much rarer type of the disorder is Becker muscular dystrophy, which affects about 1 in 10,000 boys. The onset of Becker muscular dystrophy is slower, and the symptoms tend to start later in childhood. Other rare forms of muscular dystrophy can affect both girls and boys.
What are the causes?
Both Duchenne and Becker muscular dystrophies are caused by an abnormal gene carried on the X chromosome (see Gene disorders). Girls may carry the defective gene, but they do not usually have the disorder because they have two X chromosomes, and the normal X chromosome compensates for the defect in the gene on the other.
Normally, this gene is responsible for the production of a protein called dystrophin, which is necessary for healthy muscles. In Duchenne and Becker muscular dystrophies, the gene is abnormal, resulting in a deficiency of the protein and damage to muscle. In Duchenne muscular dystrophy, almost no dystrophin is produced. However, in Becker muscular dystrophy some dystrophin is present, accounting for the difference in severity between the two conditions.
What are the symptoms?
The symptoms of Duchenne muscular dystrophy usually appear around the time a child would begin to walk. Late walking is common; often an affected child does not begin to walk until about 18 months and then will fall more frequently than other children. The more obvious symptoms of the disorder may not appear until the child is between 3 and 5 years old and may include:
Difficulty climbing stairs.
Difficulty getting up from the floor. Characteristically, a child will use his hands to “walk up” the thighs.
Large calf muscles and wasted muscles at the tops of the legs and arms.
Mild learning disabilities.
The symptoms are progressive, and a child may be unable to walk by the age of 12. The symptoms of Becker muscular dystrophy are similar but usually do not appear until later in childhood or adolescence. This condition progresses more slowly; some of those affected are still able to walk until their 30s or later.
Are there complications?
In Duchenne muscular dystrophy, the heart muscle may become thickened and weakened. The limbs may also become deformed, and abnormal curvature of the spine may develop (see Scoliosis). In the later stages, a child may have difficulty breathing, and there is an increased risk of chest infections that can be life-threatening.
How is it diagnosed?
If a pregnant woman is known to be a carrier of the disease, she will probably be offered antenatal testing to determine whether the fetus is affected (see Antenatal genetic tests).
In most cases, muscular dystrophy is suspected only when symptoms appear. A blood test to look for the abnormal gene may be used to confirm the diagnosis. If the result is positive, a further blood test may be performed to look for evidence of muscle damage. Electromyography (see Nerve and muscle electrical tests), which records electrical activity in muscles, may be performed. A muscle biopsy may be carried out, in which a small piece of muscle tissue is removed for examination. Tests will also be done to find out if the heart is affected, including a recording of the electrical activity in the heart (see ECG) and ultrasound scanning (see Echocardiography).
What is the treatment?
The treatment for muscular dystrophy is directed at keeping an affected child mobile and active for as long as possible. A team of professionals, including a physiotherapist, a doctor, and a social worker, can provide support for the whole family. Physiotherapy is important to keep the limbs supple, and supportive splints may be used. Some children require mobility aids. If a child develops scoliosis, surgery may be necessary to straighten the spine.
Children with muscular dystrophy and their families usually need a great deal of psychological support. Genetic counselling is offered to parents of an affected child who wish to have another baby and to sisters of boys affected by the disorder.
Duchenne muscular dystrophy may be fatal before the age of 20. Becker muscular dystrophy has a better outlook; people usually live into their 40s or later.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.