BECKER MUSCULAR DYSTROPHY

by Dr D Gardner-Medwin, Paediatric Neurologist

What is Becker muscular dystrophy?

The muscular dystrophies are a group of genetic disorders which involve muscle weakness. The Becker type was first recognised in 1956 and is now known to be a milder variant of the better known Duchenne type of md. However, some people with this condition have until recently been diagnosed as having the 'limb-girdle' type of md. Becker md is slowly progressive and affects only males.

What causes it?

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 md. In Becker md, a milder fault makes the dystrophin molecule smaller (or 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 very good test for the diagnosis of Becker md.

What are the symptoms?

These usually begin very mildly in childhood; often cramps on exercise are the only problem at first but a few affected boys 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.

Men 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. Over a period of many years some muscles become weak and wasted, especially certain muscles of the shoulders, upper arms and thighs, while others which 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 md.

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 md would theoretically be effective also in the Becker type, although a complex or troublesome form of treatment might be more difficult to justify in the milder disorder.

So what can be done?

Active exercise strengthens normal muscle fibres (and the great majority are normal in the early years of Becker md). 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 md. 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).

Sessions of calf muscle massage or compression with patent air-filled leggings may help too, although 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.

Will there be problems at school?

Most young men with Becker md leave school without having had any major muscular problems except that they are usually slow at running in their teens and not very successful at P.E. or games. In many cases the problem is recognised and diagnosed at around the age of 20. A few boys with Becker md also have learning problems, usually of a mild degree but sufficient sometimes to limit their academic success at school. It is important to realise that this is not true of most Becker boys, but when the problem does exist it is sensible to recognise and assess it early and to arrange the best possible plan to provide the right educational help. Unlike the muscle weakness, any learning problem will not get worse as the years go by.

What about work?

People with Becker md have been employed in a range of jobs from steel workers to research scientists although occupations requiring a considerable amount of physical activity are not feasible for most people who have Becker md. It is important for people to plan their careers on the basis that their existing physical capabilities are unlikely to improve and will eventually gradually decline. The important principles are to work for the best possible educational qualifications at school, to make good use of any opportunities for further education and then either to plan a career that will depend as little as possible on physical strength and mobility, or to be prepared to re-train and change jobs appropriately as time goes on.

How is Becker md inherited?

The disorder is inherited as an X-linked recessive trait. This means that it affects 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. However, all the daughters of affected males are carriers of the gene and may transmit the disorder to the following generation.

How early can it be diagnosed?

Once Becker dystrophy is known to affect one male in a family it is possible by simple blood tests to identify it or rule it out in any other boys at risk from birth onwards. 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.

Can any carriers in the family be identified?

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 samples from relatives are not available, it may be possible only to calculate for each potential carrier her statistical risk of having an affected son.

Where can I find more information?

A GP or hospital consultant can refer a person with Becker md to a Muscular Dystrophy Campaign Muscle Centre, if there is one in the region. A Muscle Centre is staffed by specialists in neuromuscular conditions. They have the facilities to provide the most up-to-date diagnostic information and also specialised clinics which children and adults alike will be able to attend.

It is also possible for families to meet each other there; families who are having similar experiences and who can share similar problems. A Muscular Dystrophy Campaign family care officer is on hand to help families liaise between the various professionals e.g. physiotherapists, occupational therapists, social workers, teachers etc. Even if there is no Muscle Centre nearby there may be a muscle specialist in the area who will be able to provide the care needed.

As Becker md is a fairly rare condition, and one about which people have often not heard, parents of a child with Becker and adults with Becker can feel rather isolated. However, they will find that there are many people in similar positions and some who have already dealt with situations that they are encountering. A family care officer or hospital consultant may be able to put people in touch with like-minded families.

There is no one best way of coping, but there are specialists on-hand, especially family care officers, who cover most of the UK and who have a lot of experience with muscular dystrophy.