Duchenne muscular dystrophy

What is Duchenne muscular dystrophy?

Duchenne muscular dystrophy (DMD) is an inherited (genetic) condition which affects the muscles, causing muscle weakness. It is a serious condition which starts in early childhood. The muscle weakness is mainly in the 'proximal' muscles, which are those near the trunk of the body, around the hips and the shoulders. This means that fine movements, such as those using the hands and fingers, are less affected than movements like walking.

The muscle weakness is not noticeable at birth, even though the child is born with the gene which causes it. The weakness develops gradually. It usually shows up in early childhood. Symptoms are mild at first but increase as the child becomes older.

The name Duchenne comes from the doctor who first studied this condition.

How common is Duchenne muscular dystrophy?

About 1 in 3,500 boys in the UK are born with DMD. There are other types of muscular dystrophy too, which are rarer. See the separate leaflet called Muscular Dystrophies for more details.

What causes Duchenne muscular dystrophy?

The cause is a genetic change which affects the muscles. Muscles contain a chemical (protein) called dystrophin, which is necessary for muscles to function properly. People with DMD have a shortage of dystrophin in their muscles. The lack of dystrophin leads to muscle fibre damage and a gradual weakening of the muscles. The shortage of dystrophin is caused by a faulty gene.

How does a faulty gene cause DMD?

The body is made of cells and each cell has a 'control centre' which contains genes. The genes are made of DNA. The genes control how the cells make proteins. Every cell contains many different genes and makes many different proteins. One of these proteins is the dystrophin protein which is involved in DMD.

In DMD there is a fault in the gene which makes dystrophin. So the muscle cells cannot make dystrophin (or they make only a little of it). This leads to muscle damage, as explained above.

How is Duchenne muscular dystrophy inherited?

Each person inherits a set of genes from their father and another set from their mother. The genes have been copied from the parents' cells into the child's cells.

Genes are found on 'chromosomes', rather like houses on a street. The DMD gene is located on a chromosome called the X chromosome. Boys have one X chromosome and one Y chromosome; girls have two X chromosomes.

DMD is inherited in a pattern called 'X-linked inheritance'. The DMD gene is 'carried' by women but does not usually cause problems in girls or women (with rare exceptions, below). This is because of there being two X chromosomes in women: one X chromosome has the 'faulty' DMD gene; the other X chromosome has a normal gene, which compensates for the faulty one.

In contrast, boys with the DMD gene do not have a second X chromosome and so they cannot compensate for the faulty gene. Therefore, boys with the DMD gene always have symptoms of the disease.

The DMD gene can be passed on from parent to child. For a woman who carries the DMD gene, there is a 1 in 2 chance that her sons will have DMD, and a 1 in 2 chance that her daughters will carry the gene.

X-linked inheritance pattern

If my child has DMD, does that mean that other family members have the DMD gene?

Not necessarily. In about half of DMD cases, the fault in the child's gene has not come from the parent. Instead, the fault has arisen while the child's cells were being formed. This can happen if a 'mistake' is made when the parents' genes are copied into the cells which will make the child.

About half the children with DMD will not have family members carrying the gene. DNA testing and specialised genetic advice can help you find out whether the Duchenne gene is carried by other members of the family.

What are the symptoms of Duchenne muscular dystrophy?

The symptoms usually start around age 1-3 years. Parents may notice:

• The child having difficulty with walking, running, jumping and climbing stairs. Walking may look different with a 'waddling' type of walk. The boy may be late in starting to walk (although many children without DMD also walk late).

• When you pick the child up, you may feel as if he 'slips through your hands', due to looseness of the muscles around the shoulder.

• The calf muscles may look bulky, although they are not strong.

• As he gets older, the child may use his hands to help him get up, looking as if he is 'climbing up his legs'. This is called 'Gower's sign'.

• Some boys with DMD also have a learning difficulty. Usually this is not severe.

• Sometimes, a delay in development may be the first sign of DMD. The child's speech development may also be delayed. Therefore, if you have a boy whose development is delayed, you may be offered a screening test for DMD. However, DMD is only one of the possible causes of developmental delay - there are many other causes not related to DMD.

How is Duchenne muscular dystrophy diagnosed?

The diagnosis may be suspected because of the child's symptoms (above). When looking for signs of DMD, it is important to watch the child running and getting up from the floor - the muscle weakness is more noticeable during these activities.

Tests are needed before DMD can be diagnosed. The first step in making the diagnosis is a blood test. This tests for creatine kinase. Children with DMD always have a very high level of creatine kinase (about 10-100 times normal). Therefore, if a child's creatine kinase level is normal then DMD is ruled out. If the creatine kinase level is high, further tests are needed to see whether this is due to DMD or to some other condition.

The next step in diagnosing DMD involves either a muscle biopsy and/or genetic tests:

• A muscle biopsy involves taking a small sample of a muscle, under local anaesthetic. The sample is examined under a microscope, using special techniques to look at the muscle fibres and the dystrophin protein.

• Genetic tests are done using a blood sample. The DNA in the blood is tested to look at the dystrophin gene. This test can diagnose most cases of DMD.

What is the treatment for Duchenne muscular dystrophy?

There is no cure for DMD at present. However, treatments can help. Here is an outline of the treatment you/your child may be offered. The treatment is described here according to age group, although there will be some overlap and the ages given are only a rough guide.

Preschool age

Usually, at this stage, your child will be well and not need much treatment. What you will usually be offered is:

• Information about DMD. You may wish to be in touch with patient support groups or other families with DMD (see below).

• Referral to a specialist team so that your child's health can be monitored. The specialist team may include a doctor who specialises in the medical care of children (a paediatrician), or a specialist in muscle and nerve conditions (a neurologist), and a physiotherapist and specialist nurse.

• Advice about the right level of exercise for your child.

• Genetic advice for the family. You may wish to have tests to see whether anyone else in the family has the DMD gene. This may be important to families who are thinking of having more children.

Age 5-8 years

At this age, some support may be needed for the legs and ankles. For example, using night-time ankle splints, or with a longer brace called a knee-ankle-foot orthosis (KAFO).

Treatment with medication called corticosteroids (or steroids) can help to maintain the child's muscle strength. This involves taking medication such as prednisolone or deflazacort as a long-term treatment, either continuously or in repeated courses. Steroid medication can have side-effects, so the pros and cons of this treatment need to be weighed up and the treatment needs to be monitored for side-effects. See the separate leaflet called Oral Steroids for more details.

8 years to late teenage years

At some time after the age of 8 years, the child's leg muscles become significantly weaker. Walking gradually becomes more difficult and a wheelchair is needed. The age at which this happens varies from person to person. Often it is around age 9-11 years, although with corticosteroid treatment, some boys can walk for longer.

After the child starts needing a wheelchair, this is also the time that complications tend to begin. Therefore, it is important to monitor the boy's health and to treat any complications early (see below). Your child will need regular check-ups. This may involve different specialists - for example, heart and lung checks, orthopaedic care for bones and joints, physiotherapists, and dieticians.

Practical support and equipment will be needed at this stage - for example, wheelchairs and adaptations to the child's home and school. Occupational therapists can advise about this. Various services can assist with equipment, care, holidays and breaks. There is usually provision from local health and social services. Also, there are various charities which can assist with equipment, holidays and other forms of care.

Counselling and emotional support for you and/or your child may be helpful.

Late teenage years to 20s

At this stage, muscle weakness becomes more problematic. Increasing help and adaptations are needed. Complications such as chest infections are likely to increase, so more medical monitoring and treatment are required.

What are the complications of Duchenne muscular dystrophy and how are they treated?

Anaesthetics

People with DMD need extra care if they have a general anaesthetic. Certain anaesthetic medicines can cause a harmful reaction for people who have DMD. Also, extra care for the chest and breathing is needed. It is important to have a pre-operative assessment and a senior anaesthetist providing the anaesthetic care. Always tell doctors and nurses that you have/your child has, DMD.

Osteoporosis

People with DMD may develop 'thinning' of the bones (osteoporosis). This is due to lack of mobility and also to steroid treatment. It is important to prevent osteoporosis as far as possible. A good intake of vitamin D and calcium helps keep bones strong. These can be obtained from certain foods or from vitamin supplements and by action of sunshine on the skin (which makes natural vitamin D).

Sometimes a blood test to check your vitamin D levels is advised and vitamin D supplements may be offered. See the separate leaflet called Vitamin D Deficiency for more details.

Osteoporosis which is problematic can also be treated with certain medications - for example, with bisphosphonates.

Joint and spinal complications

Muscle weakness can result in some joints becoming tight - this is called a 'contracture'. In DMD, it is often the ankle joint and Achilles tendon which become tight. This can be treated either using splints or casts (orthotic devices) or by surgical release of the tendon.

Curvature of the spine (scoliosis) can occur due to muscle weakness. Usually this happens sometime after the child needs a wheelchair. The scoliosis can cause discomfort and is not helpful for posture and breathing. Treatments which can help are a spinal brace, or surgery to the spine.

Nutrition and digestion

Some children with DMD are prone to being overweight, especially if taking steroid treatment. Teenagers and adults with DMD may be underweight, due to loss of muscle bulk. Dietary advice can be helpful in these situations.

Constipation can be a symptom for anyone who is not mobile. This can be treated with laxatives and a high-fibre diet.

In the later stages of DMD (as a young adult and older), people with DMD may have difficulty with chewing and swallowing food. They may need a careful assessment and nutritional advice or supplements. If the problem is severe then a feeding tube into the stomach (a gastrostomy) may be needed.

Chest and breathing complications

During the teenage years, the breathing muscles weaken, causing shallow breathing and a less effective cough mechanism. This can lead to chest infections, because mucus and germs (bacteria) are not cleared so easily from the chest. It is important to treat chest infections promptly - for example, by getting medical advice early and taking antibiotic medicine where needed. Also, you will be offered immunisation with influenza and pneumococcal vaccines, to help prevent chest infections. Physiotherapy can help to clear mucus from the chest.

As the breathing muscles become weaker, oxygen levels in the blood may be reduced, more so while sleeping. Because this develops gradually, the symptoms may not be obvious. Possible symptoms are tiredness, irritability, morning headaches, night-time waking and vivid dreams.

Breathing problems can be helped in various ways. There are techniques to assist breathing and coughing, which can be taught by a physiotherapist. Also, various types of equipment can be used to assist breathing. Often, what helps is a method called 'non-invasive ventilation'. This uses a mask worn over the mouth or nose and delivers air which is pressurised. The extra air pressure compensates for the breathing muscles' weakness. Non-invasive ventilation can often be used in a way which does not interfere too much with other activities - for example, it may only be needed at night or from time to time. The equipment can be portable.

There are various other methods to help improve breathing and oxygen levels. The aim is to find the one most suited to each individual.

It is helpful if breathing problems are detected and treated early; so patients with DMD will usually be offered regular 'lung function tests' once they start to have significant muscle weakness. These are simple tests which can monitor the strength of the breathing muscles and the level of oxygen in the blood.

In the later stages of DMD, the muscle weakness progresses and more support will be needed for breathing. This type of treatment has improved over recent years, which has helped to improve the quality of life and outlook for people with DMD.

Heart (cardiac) complications

Teenagers and adults with DMD may develop a heart problem called cardiomyopathy, which means weakness of the heart muscle. With DMD, the cardiomyopathy does not usually cause much in the way of symptoms. Possible symptoms are tiredness, leg swelling, shortness of breath or an irregular heartbeat. Cardiomyopathy can be helped by medication. This treatment seems to work best if started at an early stage, before symptoms are noticed. So people with DMD are usually offered regular heart check-ups, starting from early childhood. The check-ups usually involve a 'heart tracing' (an electrocardiogram, or ECG) to record the heartbeat and an ultrasound of the heart (an echocardiogram, or echo).

What is the outlook for Duchenne muscular dystrophy?

DMD is a very serious condition and it does shorten life. Because the muscle weakness increases gradually over the years, complications eventually develop. The breathing or heart problems usually become more serious for older teenagers or people in their 20s. In the past, most people with DMD did not live beyond their early 20s. Improvements in treatment have meant that life expectancy has increased. At present, average life expectancy for people with DMD is 27 years. However, there is a lot of individual variation in the severity of DMD and the individual life expectancy. The outlook (prognosis) may improve further in future, with advances in treatment.

The most serious complication, and the usual cause of death for people with DMD, is the respiratory complications, such as a severe chest infection at the stage when lung function is already poor.

Can Duchenne muscular dystrophy affect women who carry the gene?

Girls and women who carry the DMD gene are usually well and have no symptoms of DMD themselves. However, carrying the DMD gene might affect you in one of the following ways:

Passing on the gene. A woman who has the DMD gene can pass it on to her children. Normally there will be a 1 in 2 chance that the gene will be passed on to your child, as explained above. It can be helpful to have advice from a specialist in genetics (a geneticist), who can discuss your individual situation. In many cases, prenatal testing is possible, to find out whether an unborn child carries the DMD gene.

Muscle symptoms. A small number of women carrying the DMD gene may develop some muscle weakness. This probably occurs in about 3 in 100 women carrying the gene. The muscle weakness is usually mild but there is a lot of individual variation. Rarely, there can be a muscle weakness similar to that in boys with DMD. If there is a weakness, it may increase (progress) slowly over time.

We do not know why some women with the DMD gene develop muscle weakness, while others do not have any symptoms. It may be due to a process called 'X inactivation'. In this process, the 'normal' X chromosome is not active and therefore cannot compensate for the 'abnormal' X chromosome which carries the DMD gene.

Heart problems. Some women carrying the DMD gene may develop heart muscle disease (cardiomyopathy) or an abnormal heart rhythm. If this happens, it is usually milder and starts at a later age, compared to boys with DMD. At present, there is a debate about how likely this problem actually is. Recent research from the UK found that most women with the DMD gene had only very minor changes found on heart check-ups. Also, this research found no difference in life expectancy between women carrying the DMD gene and those without it. Other research suggested that 1 in 10 women with the DMD gene might develop some form of cardiomyopathy.

Therefore, some doctors are recommending regular heart check-ups for women who have the DMD gene. For example, they may suggest an ECG and an echo (explained above) once every few years, from around the age of 20. However, doctors are uncertain as to how much this monitoring is useful or necessary.

Research

There is a lot of research taking place aiming to improve treatment and perhaps find a cure for DMD. Some aspects of current research are:

• Establishing the best type and dose of steroid treatment to help maintain muscle strength.

• Whether gene therapy can be used to cure DMD or prevent loss of muscle. There is a recent trial involving a type of gene therapy called 'exon skipping'. The first results are promising, although this research is still in a very early stage.

• Stem cell therapy - eg, using cells that produce normal dystrophin.

• A form of medicine to help produce a protein called 'utrophin' which is similar to the missing dystrophin.