DUCHENNE MUSCULAR DYSTROPHY

by Dr D Gardner-Medwin, Paediatric Neurologist

What is Duchenne muscular dystrophy?

It is one of more than 20 types of muscular dystrophy. All the muscular dystrophies are caused by faults in genes (the units of inheritance which parents pass on to their children) and they cause progressive muscle weakness because muscle cells break down and are gradually lost.

The Duchenne type affects only boys (with extremely rare exceptions) and is known to result from a defect in a single important protein in muscle fibres called dystrophin. It is named after Dr Duchenne de Boulogne who worked in Paris in the mid-19th century and was one of the first people to study the muscular dystrophies.

How serious is it?

Most affected boys develop the first signs of difficulty in walking at the age of 1 to 3 years; by about 8 to 11 years (rarely earlier or a little later) they become unable to walk.

How common is it?

About 100 boys with Duchenne muscular dystrophy are born in the United Kingdom each year. There are about 1500 known boys with the disorder living in the UK at any one time. For the general population the risk of having an affected child is about 1 in every 3500 male births.

Is there no treatment?

Unfortunately no cure has yet been discovered. Much can be done to help limit the effects of the muscular dystrophy but no treatment is known which affects the actual loss of muscle cells. Intensive research to find a cure has been carried on for many years.

The discovery of dystrophin in 1987 has given this new impetus because scientists now have a really practical starting point in their search for a way to influence the genetic fault or to find a way around it. No one can predict how soon this may be achieved or which of the new ideas which are constantly being tested will prove worthwhile. Details of how far we have progressed in our research into DMD can be found under the research section of this web-site.

How is Duchenne muscular dystrophy diagnosed?

Reliable tests are available once somebody has recognised that the problem with walking might be due to this relatively rare condition. All affected boys have very abnormally high levels of an enzyme called creatine kinase in their blood. Most hospital laboratories can do this test. But there are other even rarer causes of a positive creatine test, so for a specific diagnosis in families with no previous affected member, a muscle biopsy is generally regarded as essential.

Only specialised hospital departments have the facilities for doing muscle biopsies of a high enough quality to give fully reliable results. Nowadays measurement of dystrophin in muscle is being used increasingly in specialised units but it is not usually essential for the diagnosis.

In addition a quite separate blood test can be done in specialised genetic units to examine DNA, which is the chemical material of which genes are made. In about two thirds of boys with Duchenne muscular dystrophy a deletion or little piece missing from the Duchenne gene can be identified by this test, but this is generally of more use in genetic counselling for the family than in the initial diagnosis. However, as we become more familiar with the significance of their particular deletion in predicting the likely severity of the muscular dystrophy in each individual, we may be able to make confident diagnoses in the future without the need for muscle biopsy, but only in those boys who have a clear-cut deletion.

Can we be sure there is no mistake in the diagnosis?

There are only two conditions which are at all likely to cause any confusion in diagnosis to a doctor experienced in Duchenne dystrophy - and both of these are other types of muscular dystrophy. The autosomal recessive type is about 40 times rarer than the Duchenne type in boys and is somewhat similar, but in this condition dystrophin is normal.

The Becker type of muscular dystrophy is a milder variant of dystrophin deficiency and there is much overlap in severity with the Duchenne type. Duchenne dystrophy is about three times more frequent. It may be difficult in very young children to gauge severity at first, but in the great majority of cases the position is clear. In the mildest cases of Duchenne and the most severe of Becker dystrophy the distinction lies only in the name.

How is it inherited?

Duchenne muscular dystrophy is caused by an X-linked gene (that is, the gene is on the X chromosome; girls have two of these and boys only one). This means that only boys are affected but that their mothers are often carriers.

Actually in almost half of all affected boys nowadays it turns out that the faulty gene has arisen by a change in the gene or 'mutation' in the boy himself and no other member of the family carries it. But this is difficult, and sometimes impossible, to prove and can be decided only after careful and expert assessment of the family. In just over half of all cases the mother carries the gene but is usually not herself affected by it. Such women are known as 'carriers'.

Each subsequent son of a carrier has a 50:50 chance of being affected and each daughter has a 50:50 chance of being a carrier herself. One of the most important things that needs to be done soon after the diagnosis of a boy with Duchenne muscular dystrophy is to seek genetic advice and appropriate tests for those members of the family who are at risk of being carriers.

A small number of female carriers of the gene have a mild degree of muscle weakness themselves and are then known as "manifesting carriers". Rarely this may even cause a pattern of "limb girdle" weakness.

How can we be sure that no other boy in the family has it?

If a boy of any age has a normal creatine kinase blood test you can be sure that he is not affected and will never develop the condition.

Can any carriers in the family be identified?

This is less easy but geneticists can identify from the family tree which women are at risk of being carriers. A combination of creatine kinease and DNA blood test allows the great majority of such women to be either identified as carriers or given a strong reassurance that their risk is very low.

Can it be diagnosed before birth?

Often, but not always. At present this is possible normally when DNA studies, performed beforehand in all the necessary members of the family, give precise information which allows the status of the unborn baby to be identified when his own DNA is studied in a chorion villus biopsy. This test is performed on a tiny piece of the developing placenta, usually at about the 10th week of pregnancy.

Otherwise the best that can be done is to discover whether the fetus is male or female by the chorion villus biopsy at 10 weeks, or by amniocentesis at about 16 weeks, but this does not show whether a male is affected or not.

What medical help will he need now?

Very little in the early days after diagnosis. Active exercise is important but not necessarily with medical supervision. Overweight is a common problem in later years, and is best prevented by establishing sensible eating habits for the whole family as early as possible. The most important way in which a doctor can help at this stage is to assist you, as parents, to learn as much as you can about Duchenne muscular dystrophy and, in particular, provide or arrange genetic advice. It may also be possible at this stage to set up an arrangement for long term follow up for continuing discussion and help.

What medical help will he need later?

Regular supervision will become increasingly important as the years go by. Early identification of contractures (shortening of muscles) and spinal curvature will allow these to be treated more effectively and, indeed, preventive treatment may be recommended. The physiotherapist will play an important part in this and can advise you about exercises. Special equipment may be prescribed to maintain independence. Good general health, regular active exercise and not being overweight are obviously helpful when you need to maintain what muscle strength you have.

What can we as parents do to help him?

Learn all you can about muscular dystrophy and be prepared to go on learning over the years. It will give you confidence and help you to foresee and prevent problems and to make balanced decisions.

Help him to enjoy active exercise so that it becomes a life-long habit; don't worry about how much it is helping the muscles at first. Active exercise means making the muscles work quite hard (but without overdoing it) and this helps to strengthen them. Games, swimming and walking for pleasure are some of the best ways to start. Passive exercise means stretching and it becomes necessary a bit later (usually with the help and advice of a physiotherapist) to prevent contractures.

Think about the whole family's eating habits; a healthy diet will prevent overweight and prevention is far easier than cure. As boys with muscular dystrophy become less active they often gain weight because they need much less food than their active friends and siblings and yet they often go on eating as much as ever. Try to get your whole family out of the unhealthy British habit of having regular sweets, fizzy drinks and junk food between meals. Persuade grandparents that treats should be interesting things to do, not things to eat.

Incidentally, because tobacco smoke can be quite harmful to a child's lungs especially if he already has breathing difficulty, it is a good idea for people in the family to try and give up smoking if they have a boy with Duchenne md so that during his later years he will not have this added problem with his chest.

Above all, make sure that his life is packed full of interesting activities, hobbies and friendships; keep open house to all his friends; encourage his education, skills and independence and make sure that your other children share in these benefits.

Try to translate the hope that we all have - that a treatment will be found - into really practical optimism in this way. In any case there is always going to be much that he can do - concentrate on encouraging his skills and interests in every way you can.

You will probably find it easier to make his life interesting and varied if yours is too. Try to help all the family to develop their interests and activities and not to become too wrapped up in the problem of muscular dystrophy.

Sometimes unaffected brothers and sisters miss out on the attention and affection they need because their parents are preoccupied. Time devoted to them and also, very importantly, to each other will make your family life a more secure and stimulating base for your son. There will not be time for everything; sometimes a little healthy neglect will help to develop your children's sense of independence, but try to spread it as thinly and fairly as you can.

It can of course often be healthy and natural to act as if the muscular dystrophy wasn't there - for example making special plans for him to do something exciting or difficult when it could be easier not to bother. But this means accepting and conquering the problem, not opting out.

What plans will we have to make for the future?

The previous paragraphs may give you some ideas about planning to help your son. One practical problem that needs to be planned for in advance is how he is going to get about in your house and remain as independent as possible when he can no longer climb stairs or when he uses a wheelchair. Will he be able to go without help to the toilet or his bedroom? Will he be able to use the bath etc.? Solutions can be found to these problems but special equipment may be needed and sometimes the family home needs adaptations or even an extension.

The ideal house for a person in a wheelchair is sometimes a bungalow and you should consider whether you might try to find one, but for other people different solutions may be better. Local authority grants, building permission and the building work itself can all take an unbelievably long time to arrange and it is vital to start thinking about them well beforehand. It is also crucial to seek skilled advice before making an expensive decision about your home. The Muscular Dystrophy Campaign, perhaps through one of their Family Care Officers, may be able to help you get this advice.

What about school?

Most children with muscular dystrophy cope pretty well in their local infants' school and in their first few years at junior school. If walking becomes too precarious or access to classrooms, toilets or dining room becomes too difficult, some schools will make special arrangements or even structural alterations. Local authority transport to and from school can be arranged if necessary. If the school is too unsuitable, an alternative mainstream school in the district or a special school for disabled children might provide the answer.

When he leaves school your son will naturally find it difficult to do a job requiring any muscle strength, and his leisure activities will be restricted in the same way. From the earliest days at school his education is therefore going to be doubly important so that his talents, whether as an artist, organiser, writer or whatever, can be fully developed. Higher or further education often offers good opportunities for school leavers.

Some boys with Duchenne muscular dystrophy are found also to have learning difficulties. This problem is rarely severe and when it does occur, unlike the muscle weakness, it never becomes worse as time goes by. In those boys who have the problem, language and communication skills are often the main difficulty. Manual skills, design sense and imaginativeness are often excellent, which is perhaps why many young men with Duchenne muscular dystrophy become very good artists and model makers.

As parents you can work with the school to discover and develop your son's best talents as well as helping him to learn to cope with tasks he finds difficult.