Muscular Dystrophies - An Overview

What is muscular dystrophy?

Muscular dystrophy (MD) is the name given to a group of disorders which cause muscle weakness. There are many different types of MD. The different types vary as to how mild or severe they are, and which muscles they affect.

What causes muscular dystrophy?

The cause is an abnormal or 'faulty' gene.

Genes are made from a biological material called DNA. Genes are the 'control centre' of each cell in the body, including muscle cells. The genes control the proteins (chemicals) that the cell makes. Some genes control the proteins needed for muscle fibres to work properly. It is these genes which are involved in MD.

The 'faulty' gene in MD means that one of the proteins needed by muscle cells cannot be made correctly - the protein will either be lacking, or will be a 'faulty' protein that does not work well. This leads to damaged muscle fibres and to muscle weakness. Depending on the exact type of faulty gene and faulty protein, different types of muscle weakness result. This is why there are different types of MD.

Is muscular dystrophy inherited?

Sometimes. Because MD has a genetic cause, it can be inherited - meaning that the faulty gene can be passed on from parent to child. However, in many cases, the faulty gene occurs only in one individual, with the rest of the family having normal genes.

In some types of MD, family members may 'carry' the faulty gene without having the muscle weakness themselves.

If you or a family member have MD, you will usually be offered tests and specialist advice from a 'geneticist' (a doctor who specialises in diagnosing genetic conditions). This can give more information about the particular 'faulty gene' and the exact type of MD that you or your relative has. This information can then be used to help work out whether the 'faulty gene' could affect other family members.

What are the symptoms of muscular dystrophy?

The main symptom of MD is muscle weakness. This varies greatly between the different types of MD.

Symptoms may start anywhere between birth and middle age, depending on which type of muscular dystrophy is involved. In young babies, the muscle weakness may be noticed as 'floppiness' of the baby. In older babies and young children, the weakness may show up as as the child having a delay in 'motor milestones', meaning a delay in learning to hold up their heads, sit up, crawl or walk. (But note that there are many other causes of delayed motor milestones apart from MD.)

There are also differences as to which parts of the body are affected. Different types of MD affect different muscle areas (known as muscle groups) of the body - see the picture below.

The muscle weakness itself may be mild, moderate or severe. The different types of MD vary as to how quickly or slowly the weakness progresses.

Sometimes there may be symptoms other than muscle weakness. These are:

• Muscle wasting - where the muscles become thin.
• Muscle hypertrophy - where the muscles are bulkier than normal, even though they work less well.
• Aches or pains in the muscles.
• Contractures - where joints are tight, due to tightness of the muscles or reduced movement of the joints.
• Developmental delay in a child (this means that the child's 'milestones' of development are later than usual).
• Some types of MD can affect the heart. In some cases, there may be symptoms of heart disease without much in the way of muscle weakness.

What are the different types of muscular dystrophy?

Duchenne's muscular dystrophy

The most common and most severe type of MD is a type called Duchenne's muscular dystrophy (DMD). This causes muscles weakness mainly in the legs and upper arms. The weakness starts early in childhood and gradually increases, affecting the child's ability to walk.

DMD usually affects boys rather than girls. Women and girls can carry the 'faulty' Duchenne gene, but don't normally have the muscle weakness or any symptoms. However, in rare cases, girls or women with the Duchenne gene can develop muscle weakness.

Generally, boys with DMD need to use a wheelchair from around the age of twelve years. From their late teenage years there can be complications, such as weakness of the breathing or heart muscles, which need treatment. Rarely, heart muscle weakness can occur in women carrying the DMD gene.

The heart and breathing problems eventually become more serious and shorten life. Men with DMD usually live into their late twenties, or sometimes longer.

See separate leaflet called 'Duchenne's Muscular Dystrophy' for more information.

Becker's muscular dystrophy

Becker's muscular dystrophy (BMD) is similar in many ways to DMD, but is less severe. Symptoms start in the teenage years or early twenties. The weakness progresses slowly, so that in their 40s and 50s, men with this condition may have difficulty walking. Weakness of the heart and breathing muscles can occur and may need treatment.

As with the Duchenne type, BMD usually affects only boys. Girls and women may carry the gene but don't usually have symptoms. Rarely, women or girls with the Becker gene may have muscle weakness or heart problems.

Limb girdle muscular dystrophy

The limb girdle muscular dystrophies (LGMDs) cause weakness in the muscles around the top of the arms and legs, which is why 'limb girdle' is used in the name of this condition. There are many different types of LGMDs. They can affect men or women. The symptoms and muscle weakness vary a great deal, depending on which particular form of LGMD you have.

Some types of LGMD can cause an abnormal heart rhythm or weakness of the heart and breathing muscles. These may need monitoring and treatment.

For more information on the different types of LGMD, see the Muscular Dystrophy Campaign website (below).

Facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is also called Landouzy-Dejerine or facioscapuloperoneal muscular dystrophy. FSHD can affect both men and women.

FSHD affects the muscles of the face, shoulder and upper arm. Sometimes the legs may be affected too. Symptoms usually start around age 40-50 years. The degree of muscle weakness varies a lot from person to person. About 3 in 10 people with FSHD don't notice any symptoms. About 1 in 10 people with FSHD eventually require a wheelchair. Most people with FSHD have symptoms somewhere in between these two extremes. Overall, the outlook is good and FSHD does not normally affect a person's lifespan.

FSHD may be noticed as weakness of facial muscles. For example, the person's eyes may remain slightly open when asleep, or they may be unable to close their eyes tightly. They may have difficulty in pursing the lips, as in blowing up balloons or playing a wind instrument. Teenagers or adults with FSHD may have aching shoulders, rounded shoulders and thin upper arms.

Rarely, people with FSHD may have an abnormal heart rhythm, which may need monitoring or treatment.

Emery-Dreifuss muscular dystrophy

Emery-Dreifuss MD starts in childhood or adolescence. It can affect the muscles of the shoulders and upper arms, making it difficult to lift heavy objects. Also, the muscles in the lower leg are affected, which may cause tripping over when walking. Contractures (tightness) of the muscles and joints can also occur. Emery-Dreifuss MD usually progresses (increases) very slowly. People who have this condition may need a wheelchair later in life.

Emery-Dreifuss MD sometimes affects a part of the heart which controls the heart rate. This may cause a slow heartbeat (called 'heart block') and symptoms of tiredness, giddiness or fainting. This can be treated with a heart pacemaker. For this reason, regular heart checks are recommended for people with Emery-Dreifuss MD.

Congenital muscular dystrophy

Congenital muscular dystrophy (CMD) is rare (affecting about 1 in 50,000 babies). It causes muscle weakness early in life - within the first six months of birth. The first symptoms are poor head control and weak muscles, which make the the baby seem floppy. There may be joint problems called 'contractures' (stiff joints), due to the baby not being able to move the joints enough.

There are different types of CMD, which vary from person to person in how severe they are, and in whether or not they progress (get worse). In many cases, CMD is not progressive, so that although the child continues to have difficulties, their muscle strength improves with time, and the child may have a normal lifespan.

Some types of CMD are more severe or progressive. In these cases, the muscle weakness is more severe, and the child may have other problems such as seizures, learning difficulties, breathing problems, and a poorer outlook.

Oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) usually starts around the 50s or 60s. It causes a weakness in the eye and throat muscles. The first symptoms are droopy eyelids and difficulty swallowing. Later on, after many years, mild limb weakness around the shoulders and hips may also develop.

There are various types of treatment that can help with the eyelid and swallowing problems.

How is muscular dystrophy diagnosed?

Usually it is first suspected because of symptoms: a muscle weakness is noticed by the patient, family or a doctor. Also, if a child has delayed motor milestones (as mentioned above), a doctor may advise testing for MD, even though the problem could be due to another cause.

MD may be diagnosed using one or more of the following tests:

• A blood test for creatine kinase (CK) - in many types of MD, the blood level of CK is very high.
• A muscle biopsy - this involves taking a small sample of muscle under local anaesthetic. The sample is examined under the microscope and the muscle proteins may be tested.
• Genetic analysis - this involves a testing a person's DNA using a blood sample. It can detect many (not all) cases of MD.
• An electromyogram (EMG) - this is a recording of the electrical activity in a muscle.
• Muscle ultrasound is used to look for suspected CMD.

What else could it be?

There are other medical conditions which cause muscle weakness. These are:

• Conditions called 'myopathies' - in which there is muscle weakness. Some myopathies are temporary problems and are not genetic.
• Other conditions called 'neuromuscular disorders'. This is the name for a group of conditions which affect nerves, muscles or both. See the Further help and information section (below).
• Myotonic dystrophy. This may be classified as a type of MD or as a neuromuscular disorder. It affects the 'small' muscles, such as those in the face, jaw, neck, and hands. Myotonic dystrophy may start at any age from birth to old age. It can affect both men and women. (More information about this condition is on the Muscular Dystrophy Campaign website, details below.)
• Distal myopathies. These are very rare forms of muscle weakness affecting the 'distal' muscles, which are those of the hands and feet. There are different types. Most are very mild.

How is muscular dystrophy treated?

There is no cure for MD, although there are treatments which can help. The treatment offered will depend on what type of MD you (or your child) has.

Firstly, you will usually be referred to a specialist, for tests and diagnosis. This may be a neurologist (a specialist in muscle and nerve conditions) and/or a geneticist (a doctor who specialises in genetic conditions). In some cases, the specialist may suggest that other family members be tested to see if they carry an MD gene.

At present, the MDs cannot be cured. However, there are many types of treatment and aids that can help with the effects of the muscle weakness. The treatment needs to be fitted to the needs of each individual and the problems that they have from their MD. As a general guide, treatment may involve:

• Physiotherapy - to help keep the joints mobile.
• For some types of MD such as Duchenne type and LGMD, treatment with steroid medication can help to maintain muscle strength.
• Practical aids or help may be needed; for example, a splint, wheelchair or equipment for the home.
• For some types of MD, regular check-ups are needed to assess and treat any complications.
• Treatment of any specific problems, such as contractures (joint stiffness), heart or breathing problems.

There is a lot of research into MD at present, and new treatments may be available in the future.

Further help and information

The Muscular Dystrophy Campaign

61 Southwark Street, London SE1 0HL
Helpline: 0800 652 6352
Web: www.muscular-dystrophy.org
This is a UK charity for all MDs, neuromuscular disorders and related conditions. It funds research, offers help and advice, and provides information and support.

References

• Muscular Dystrophy Campaign: a UK charity giving information and links for all types of muscular dystrophy and related conditions.
• Emery AE; The muscular dystrophies. BMJ. 1998 Oct 10;317(7164):991-5.
• Manzur AY, Muntoni F; Diagnosis and new treatments in muscular dystrophies. J Neurol Neurosurg Psychiatry. 2009 Jul;80(7):706-14. [abstract]