BECKER MUSCULAR DYSTROPHY
Fact Sheet # 01
Is Becker Muscular Dystrophy also known by other names?
No, the condition is only referred to as Becker Muscular Dystrophy, abbreviated as BMD.
What is Becker Muscular Dystrophy?
The muscular dystrophies are a group of genetic disorders that involve muscle weakness. The Becker type was first recognised in 1956 and is now known to be a milder variant of well-known Duchenne type of muscular dystrophy. (Please note that a separate MDF Fact Sheet is available on Duchenne MD). Some individuals with this condition have, however, until recently been diagnosed as having the 'limb-girdle' type of muscular dystrophy. Becker muscular dystrophy is slowly progressive and generally affects males only.
What causes Becker Muscular Dystrophy?
A fault in a particular gene, carried on the X chromosome, leads to the formation of a faulty protein in muscle fibres. This protein, called dystrophin, is absent or severely abnormal in Duchenne muscular dystrophy (DMD). In Becker muscular dystrophy a milder fault makes the dystrophin molecule smaller (occasionally larger) or less abundant than normal. The function of dystrophin in the muscle fibre is not yet understood, but when it is abnormal the muscle fibres gradually break down and the muscles slowly become weaker. These dystrophin abnormalities in muscle provide a good test for the diagnosis of Becker muscular dystrophy.
What are the symptoms?
There is a mild onset during childhood. Cramps on exercise are often the only problem at first but a few affected individuals are late in learning to walk and from early childhood are unable to run very fast. Later, in the teens or twenties, muscle weakness becomes evident causing difficulty in rapid walking, running and climbing stairs. Later still it may be difficult to lift heavy objects above waist level. Individuals with typical Becker dystrophy may become unable to walk in their 40s or 50s or even later but there are less frequent and more rapidly progressive variants of Becker dystrophy in which this may happen in the 20s or 30s.
Which muscles are affected?
Over a period of years some muscles become weak and wasted, especially certain muscles of the shoulders, upper arms and thighs, while others that are less weak are often enlarged - this is usually particularly noticeable in the calf muscles. The muscles of facial expression, speech and swallowing and the involuntary muscles (for example those of the bowel and bladder) are not affected in Becker muscular dystrophy.
How is Becker Muscular Dystrophy inherited?
The disorder is inherited as an X‑linked recessive trait. This means that it affects predominantly only males but may be transmitted by unaffected female carriers of the gene to their sons. The sons of carriers each have a 50:50 chance of being affected. The daughters of carriers each have a 50.50 chance of being carriers. The mothers and sisters of affected males may be carriers and may need to be tested. The sons of affected males do not carry the gene and will not be affected or transmit the gene. All the daughters of affected males will be carriers of the gene and may transmit the disorder to the following generation. As this is a genetic condition, genetic counselling is strongly recommended. Genetic counselling provides information on the inheritance pattern, risks to other family members, prognosis, psycho-social support, as well as information about diagnostic testing, carrier testing, preclinical and prenatal testing (where available).
How is Becker Muscular Dystrophy diagnosed?
Once Becker dystrophy is known to affect one male in a family it is possible to identify it or rule it out in any other boys at risk from birth onwards, with a blood test. In most families, but not in all, prenatal diagnosis is also possible, but this is more difficult and if at all possible the situation needs to be fully assessed before a pregnancy is embarked upon.
Most carriers can be detected if blood samples from their affected male relatives and certain other key members of the family are available for comparison, using techniques of DNA analysis. Although a simpler blood test for creatine kinase is positive in many carriers, only the DNA studies can rule out the carrier state in a woman at risk (for example in the sister of an affected man). However in a few families, or if the key blood samples from relatives are not available, it may only be possible to calculate for each potential carrier her statistical risk of having an affected son.
Is there a cure?
Unfortunately there is no cure at present. Active research is proceeding to try to find a way to induce the muscles to form dystrophin. Any treatment, which may be found to be effective in Duchenne muscular dystrophy, would theoretically also be effective in the Becker type - although a complex or troublesome form of treatment might be more difficult to justify in the milder disorder.
Is there any treatment?
Active exercise strengthens normal muscle fibres (and the great majority are normal in the early years of Becker muscular dystrophy). It is important to try to keep as fit and active as possible. Regular daily exercise is better than occasional sudden bouts of exertion. Cramps during walking are only a mild nuisance in most people with Becker muscular dystrophy. If they are more troublesome it may be worth experimenting with 'night splints' (plastic splints to maintain a gentle stretch of the calf muscles overnight) or with sessions of calf muscle massage or compression with patent air-filled leggings though there is not yet a properly tried and tested treatment for cramps. In the later stages a wheelchair is likely to be needed at least for getting about independently over long distances. There is a great deal of other helpful equipment that may be useful to individuals and much can be done to help both at home and at work to make certain tasks easier by careful choice of furniture, bathroom equipment etc. Advice and help with these matters is increasingly available and the MDF will be able to put you in touch with the best sources of advice.
Is there a risk during anaesthesia?
Individuals affected with BMD have been reported to be at risk for developing a malignant hyperthermia reaction during anaesthesia. It is always recommended that the presence of a muscular disorder be mentioned to your doctor.
Has research been conducted on Becker MD in South Africa?
Yes, there is an extensive ongoing research programme on Duchenne Muscular Dystrophy at the Department of Human Genetics, University of Cape Town. Since BMD and DMD are related, this programme also covers research on BMD.
Please contact your local MDF office for further information.
Please note: The treatments and drugs mentioned in this fact sheet are for information purposes ONLY. Please consult your physician or other health care specialist for information regarding the use of any of the above. The MDF encourages duplication of this fact sheet, under the following condition: that it is duplicated in its entirety - including the MDF logo and full text. Only individuals authorised by the MDF may make changes to this fact sheet (the information "updated by" and "last update" should be completed). Alterations to this fact sheet by any other party are strictly prohibited.