Muscular dystrophy

Muscular dystrophy is the name given to a group of inherited neuromuscular conditions. They cause weakness and wasting of the muscles. This muscle wasting gets worse over time and is not reversible.

There are more than 30 different types of muscular dystrophy. Most are caused by changes to genes involved in giving strength to the muscle structure. Around 30 other neuromuscular conditions can be confused with muscular dystrophy because they have similar symptoms, but they are caused by a different mechanism.

What causes muscular dystrophy?#

Many genes help to make the proteins that protect muscle fibres from damage. Muscular dystrophy occurs when one of these genes does not work properly, and each type is caused by a different change in a gene.

Some of these gene changes are inherited from a parent. Others are new changes that occur early in development, known as spontaneous or ‘de novo’ gene changes. Spontaneous changes are not inherited, but they can still be passed on to the next generation.

Types of muscular dystrophy#

The main types include:

• Duchenne muscular dystrophy
• Becker muscular dystrophy
• congenital muscular dystrophy
• limb-girdle muscular dystrophy
• facioscapulohumeral muscular dystrophy
• myotonic dystrophy
• oculopharyngeal muscular dystrophy
• Emery-Dreifuss muscular dystrophy

Some of these are further divided into sub-types. For example, there are more than 20 types of limb-girdle muscular dystrophy. From one type to another there is variation in which muscles degenerate and in the severity of muscle degeneration.

Duchenne and Becker muscular dystrophy#

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are often discussed together because they cause similar patterns of weakness and are inherited in the same way. Both are caused by an alteration in the DMD gene, which is responsible for producing a large protein called dystrophin. Dystrophin provides a scaffold structure to muscle fibres and protects them from damage during contraction. Without this protein, the muscles gradually break down. BMD is less severe than DMD.

DMD mostly affects boys, but girls can be affected too. It is not usually noticeable before the age of two or three. Symptoms and signs include:

• delayed walking
• a tendency to stand or walk on the forefoot with the heel off the ground, often called ’toe-walking’
• frequent falls and difficulty rising from the ground or going up hills or stairs
• difficulty running and jumping
• well-developed or excessively large calf muscles, while other muscles are poorly developed
• a waddling walk and a sway-back (lordosis)

Duchenne is one of the most severe forms of muscular dystrophy. Its effects can include:

• wheelchair use, generally from around nine years of age, with total dependence on a wheelchair around the early teens
• restriction of joint motion caused by contractures (shortening of muscles and tendons), with the ankles usually affected first and the hips and knees last
• scoliosis (curvature of the spine), which often requires corrective surgery
• difficulty breathing caused by weakness of the breathing muscles; in some cases mechanically assisted breathing helps in the later stages
• heart problems in older boys, as the process can start to affect the heart muscle
• learning difficulties in a minority of boys, which can affect school work
• early death, with most affected people surviving into their 20s, some only into their teens and others beyond 30

The rate of muscle degeneration in Becker muscular dystrophy varies greatly between individuals. The signs are similar to those of DMD but are usually milder and more varied. People with BMD can often still walk at 16, and some continue to walk into early adulthood or later life. Many survive to middle age, and some have lived beyond 80. Scoliosis seldom occurs, the effect on lung function is less severe than in DMD, and heart trouble is less frequent, although it is occasionally serious.

Facioscapulohumeral dystrophy (FSH)#

Facioscapulohumeral dystrophy affects the muscles of the face (facio-), around the shoulder blades (scapulo-) and in the upper arms (humeral). It is generally considered less serious than other forms. Some muscle groups on one side of the body are often stronger than those on the other side.

Onset can occur in infancy, but symptoms may appear at any time from childhood until a person is in their 50s. Typical facial features include:

• fewer than usual facial lines, more noticeable when the muscles are in use, for example during speech
• eyes that appear slightly open during sleep due to weakness of the eye-closure muscles

Muscle weakness in the shoulders and arms may lead to:

• ‘winging’ of the shoulder blades, which stick out backwards, especially when the arms are held forward
• reduced muscle bulk between the shoulder blades
• difficulty raising the arms, sometimes first noticed in activities such as serving at tennis
• weakened ability to bend and straighten the elbow

The pattern of weakness in the lower limbs and back may include:

• lordosis (sway-back); in severe cases the abdomen may stick out and the shoulders may be held excessively far back
• foot drop due to weakness of the muscles at the front of the leg
• a tendency to trip
• a weakened ability to straighten the hips, and sometimes the knees, with a tendency for one or both knees to give out

In severe early-onset FSH, deafness is common. Changes also occur in the eyes, although these seldom affect vision; even so, people with FSH should have their eyes checked regularly. Other day-to-day difficulties include combing hair, hanging out washing, reaching high shelves and managing stairs.

Because FSH symptoms can be subtle and variable, the condition is sometimes hard to identify, and this is where genetic testing can quickly assist with diagnosis. On average FSH progresses slowly and eventually seems to plateau. In very mild cases it may not be possible to detect any progression. People affected by FSH of average severity usually keep the ability to walk and have a normal life span.

Myotonic dystrophy#

Myotonic dystrophy is the most common adult form of muscular dystrophy. It is also known as Steinert’s disease and dystrophia myotonica. Unlike the other muscular dystrophies, the weakness is accompanied by myotonia (delayed relaxation of muscles after contraction) and by various non-muscular symptoms. The first muscles affected are usually those of the face, neck, hands, forearms and feet.

Because it can affect the tissues and organs of many body systems, the effects can include:

• heart (cardiac) disease
• cataracts
• testicular atrophy, where the testes become smaller and may stop functioning
• difficulty breathing and adverse reactions to anaesthesia
• difficulty swallowing (dysphagia) and other digestive problems
• excessive daytime sleepiness
• learning difficulties
• diabetes
• thyroid problems

About half of people with myotonic dystrophy show visible signs by around 20 years of age, but a significant number do not develop clear-cut symptoms until after 50. When the condition is suspected because it is present in other family members, careful examination may reveal typical features before obvious symptoms appear.

Myotonic dystrophy is inherited in an autosomal dominant manner, which means it can be caused by inheriting just one copy of the altered gene. We inherit one copy of each gene from each parent, so when a person with myotonic dystrophy has children, there is a 50 per cent chance that each child will inherit the condition.

The condition shows an unusual pattern called ‘anticipation’ when passed between generations, in which symptoms appear at an earlier age and often with increased severity. The course varies widely, even within the same family. Some people have symptoms so mild they barely notice them and assume any weakness is normal; in some cases the only sign may be a cataract. These people still have myotonic dystrophy and can pass a more severe version on to their children.

In most cases, weakness and muscle wasting start in certain muscles and slowly spread to the shoulders, hips and thighs. The weakness rarely becomes severe until 15 to 20 years after symptoms begin. The older a person is when weakness is first noticed, the more slowly it tends to progress and the less serious the effects.

Congenital muscular dystrophy#

The congenital muscular dystrophies (CMDs) are a group of conditions that vary in severity and rate of progression. Congenital means ‘from birth’, and in most cases the first symptoms are present at birth or in the first few months.

Babies with CMD often have low muscle tone or floppiness and may have reduced movements. Other common signs are contractures (tightness) in the ankles, hips, knees and elbows, and some babies have trouble breathing and feeding. Some improvement often occurs in childhood, and the condition then shows little or no progression.

There are at least five different types of CMD, caused by changes in different genes. Both parents usually carry the altered gene but are unaffected, and the affected child inherits two copies of the altered gene, one from each parent.

Late-onset muscular dystrophies#

Many people think muscular dystrophy is only a childhood condition, but it can begin at any point in life. As well as myotonic dystrophy and FSH, three other types can appear later in life:

• Limb-girdle muscular dystrophy involves slow to fairly rapid muscle deterioration of the muscles of the pelvis and shoulders. People with this type have usually inherited the altered gene from both parents. It typically begins in the first to third decades of life and can allow a normal life span if the deterioration progresses slowly.
• Oculopharyngeal (ophthalmoplegic) muscular dystrophy is fairly rare and affects the muscles around the eyes, leading to drooping eyelids. Eventually the muscles used in swallowing may be affected. It usually appears in adulthood.
• Distal muscular dystrophy is the rarest type and is more common in some populations. It affects the small muscles of the arms and legs.

Diagnosis#

Diagnosis before the age of two or three is possible through:

• a blood test to check the levels of a protein called creatine phosphokinase (CPK); CPK is released by damaged muscle, so levels are very high in people with muscular dystrophy
• genetic testing, where a known condition runs in a family and a test can detect the genetic change in the DNA of a blood sample
• electromyography (EMG), which checks the health of the muscles and the nerves that control them by inserting a very thin needle into the muscle
• a muscle biopsy, the removal of a small piece of muscle tissue for examination under a microscope

Early diagnosis allows the most appropriate management of the condition from a young age.

Treatment#

There is currently no cure for muscular dystrophy. To help ease discomfort, reduce joint contractures and prevent or delay scoliosis, physiotherapists can advise on stretches and exercises and prescribe orthoses and other orthopaedic devices. Occupational therapists can also advise on sitting positions and activities. Such treatment can keep affected people walking for longer and maximise independence in daily living.

For some types of muscular dystrophy, medication can help manage symptoms. For example, boys with Duchenne muscular dystrophy are usually prescribed corticosteroids, which can delay the need for a wheelchair by several years on average. The risk of side effects, however, needs to be considered.

Genetic counselling#

If your child or another family member has been diagnosed with muscular dystrophy, or if it runs in your family, it may help to speak to a genetic counsellor. Genetic counsellors are health professionals qualified in both counselling and genetics. As well as providing emotional support, they can help you understand muscular dystrophy and what causes it, how it is inherited, and what a diagnosis means for your child’s health and development and for your family.

Genetic counsellors are trained to provide information and support that is sensitive to your family circumstances, culture and beliefs. If muscular dystrophy runs in your family, a genetic counsellor can explain the genetic testing options available to you and other family members. You may choose to see a genetic counsellor if you are planning a family, to find out your risk of passing the condition on, or to arrange prenatal tests.

Key points#

• The muscular dystrophies are a group of inherited conditions that cause weakness and wasting of the muscles.
• Most are caused by changes to genes involved in providing strength to the muscle structure.
• Some similar neuromuscular conditions are caused by a different mechanism.
• Many genes help make the proteins that protect muscle fibres from damage.
• Each type of muscular dystrophy is caused by a different change in a gene.

Where to get help#