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Becker Muscular Dystrophy

Also known as: Becker MD

Background

Becker muscular dystrophy (BMD) is a rare genetic condition associated with mutations (changes) in the dystrophin gene. An individual needs a range of proteins within and surrounding muscle fibres to ensure their efficient working. In BMD, a reduction in the quantity or functioning of dystrophin leads to slowly progressive damage to the muscles.

As BMD is a sex-linked disorder (with the gene located on the X chromosome), it largely affects males. Its presentation is very varied, generally in late childhood, adolescence or early in adulthood but it can be recognised earlier or later. BMD is thought to affect approximately 1 in 20,000 males. Life expectancy may be reduced, but many affected people live into their seventies.

Credits

Last updated October 2017 by Professor A Clarke, Professor and Honorary Consultant in Clinical Genetics, Institute of Medical Genetics, University Hospital of Wales, Cardiff, UK.

Although great care has been taken in the compilation and preperation of all entries to ensure accuracy, we cannot accept responsibilityfor any errors or omissions. Any medical information provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

Features of BMD include:

  • progressive muscle weakness leading to difficulty with physical activities such as standing up from sitting, climbing up steps, running or walking and, usually later, weakness affecting the upper arms and shoulders
  • joint contractures can arise from the tightening of tendons, especially the Achilles tendon
  • pseudohypertrophy (enlargement without additional strength) of muscles in the calves and elsewhere
  • cardiomyopathy (see entry Cardiomyopathies in children)
  • in the later stages of the disease, respiratory muscle weakness may lead to chest infections.

There may also be learning and/or behaviour problems in some children, including difficulty in focusing attention, verbal learning and memory.

What are the causes?

BMD is caused by mutations in the dystrophin gene. Female carriers of BMD are usually healthy. However, a small number of female carriers of the defective gene are 'manifesting carriers' (females who experience some of the effects of the disorder). These problems are usually milder than in a male and are likely to develop later in life. Occasionally, a manifesting carrier may have significant muscle weakness. Manifesting carriers may also have heart problems, which appear as shortness of breath or inability to do moderate exercise. The heart problems, if untreated, can be serious.

How is it diagnosed?

A test will be made for raised levels of creatine kinase (CK) in the blood. Elevated levels of CK are found in the blood of most individuals with BMD from childhood, sometimes from the newborn period. Further tests will be performed to confirm that the muscle weakness arises from destruction of muscle tissue rather than nerve damage. These may include:

  • genetic tests to look for mutation(s) in the dystrophin gene, usually carried out on a blood sample
  • electrical tests carried out on a muscle and/or nerve
  • muscle biopsy (examination of tissue in the pathology laboratory).

How is it treated?

Currently there is no known cure for BMD, so treatment aims to control symptoms and maintain quality of life. Physiotherapy may help to maintain muscle strength and the range of joint movement; orthopaedic devices such as braces and the use of wheelchairs can improve mobility. Surgery may sometimes be helpful if tendon contractures are problematic. Medication may also be prescribed for cardiac problems.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
BMD is inherited as an X-linked recessive trait. The dystrophin gene is located on the X chromosome, which results in mainly males being affected with the condition.

Prenatal diagnosis
This is usually possible where it is known that BMD affects the family and where the family's particular mutation in the dystrophin gene is known. Preimplantation genetic testing (or diagnosis) (PGT or PGD) may also be used by a female carrier to avoid transmitting the condition to her children.

Is there support?

Information and support in the UK for Becker muscular dystrophy is provided by Muscular Dystrophy UK (see entry Congenital Muscular Dystrophy).

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