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What are the effects and signs of the different types of Muscular Dystrophy?

Duchenne Muscular Dystrophy

This condition is caused by an X-linked recessive condition affecting the gene for the muscle protein dystrophin. This means that the abnormal gene is carried on the X chromosome. The Y chromosome, which partners with the X chromosome in boys is short and does not carry a normal copy of the dystrophin gene. This means that the condition almost always only occurs in boys.

Girls with the affected gene will have a normal gene on their other X-chromosome and will nearly always be unaffected by the abnormal gene. 2% of girls will have muscular dystrophy symptoms and they are called manifesting carriers of Duchenne Muscular Dystrophy. Symptoms are likely to be very mild and are often similar to those of Becker Muscular Dystrophy. Very rarely, a female carrier may have symptoms equivalent to the full syndrome of Duchenne Muscular Dystrophy as seen in affected boys.

The clinical features and presentation of Duchenne Muscular Dystrophy in boys is very characteristic. A common sign is big ‘hypertrophied’ calf muscles. The mean age at diagnosis is 4 years and 10 months but there will have been early signs of the condition within the first three years of life. These are:

Once walking is established children are:

Even with treatment and support to delay loss of walking, the mean age when independent walking is lost is 9 years. The condition is always severe but there is a spectrum of symptoms with some children losing mobility very early and others remaining mobile for longer. Almost all children will have lost the ability to walk by age 12 –this is called ‘loss of ambulation’ in the medical evidence. A small number of children will still be able to walk at 12 but will be expected to lose walking ability by age 16 – these may be called ‘intermediate’ cases or ‘Duchenne outliers’ in the evidence. It is not possible, in early childhood, to say which children will be in this category so intermediate or Duchenne outliers can only identified by their ability to walk at age 12.

Following loss of independent walking, some children will undergo rehabilitation to enable them to walk a minimal distance with walking aids. This will enable them to take a few steps for exercise but will not constitute a useful walking ability. They will be unable to use stairs wearing aids and will need help getting from sitting to standing to walk wearing the aids. They require supervision when wearing the aids because of the risk of falls and physical help to put them on. Maintaining minimal mobility in aids like this can help to maintain respiratory function for longer by preventing scoliosis (a deformity of the back that develops once children are confined to a wheelchair).

Eventually, even limited mobility with aids is lost and most children will be confined permanently to a wheelchair at 12 years. In the teenage years, loss of muscle tone around the spine leads to progressive and severe scoliosis sufficient to restrict breathing – this can be treated by spinal surgery. Weakness of the respiratory muscles leads to gradual decrease of Forced Vital Capacity (FVC) and they are at risk of severe chest infections and ultimately respiratory failure. Once wheelchair dependent, FVC falls gradually and sleep studies carried out once every 6 months or so are used to identify when respiratory support at night should be introduced. Night time respiratory support can prolong survival by several years. The heart muscle is also affected by the condition, when the heart is significantly affected spinal surgery cannot be performed and prognosis is much worse because lung capacity cannot be protected from increasing scoliosis. Nutritional problems are common and there is more information about this in the ‘Treatment’ section. Intelligence is at the low end of the normal range and up to 30% have learning difficulties. Children may be educated in mainstream or special schools. Death usually occurs in the 20s, though some individuals on respiratory and other supportive treatments are now surviving into their 30s.

Indicators of severe functional restriction -:

Becker Muscular Dystrophy

This condition is caused by an X-linked recessive condition affecting the gene for the muscle protein dystrophin. This means that the abnormal gene is carried on the X chromosome. The Y chromosome, which partners with the X chromosome in boys is short and does not carry a normal copy of the dystrophin gene. This means that the condition occurs only in boys. Girls with the affected gene will have a normal gene on their other X-chromosome and will not be affected by the condition.

The condition has been described as a slow motion version of Duchenne Muscular dystrophy – the symptoms are similar but the onset is later and the disease takes many years to progress. The symptoms are muscle weakness but this is much milder than in Duchenne Muscular Dystrophy and walking ability is often maintained beyond age 50. Childhood is relatively normal. The onset of symptoms and the rate at which they develop is very variable. Life expectancy is normal in all but the most severe cases. The mean age of onset is 11 years. A proportion will have had delayed motor milestones in early childhood. Typical presenting symptoms are:

These are the only symptoms likely to be experienced during childhood in the typical case and mobility is maintained into adulthood. Scoliosis does not usually occur as a result of this condition. These boys are at risk of cardiomyopathy and treatment may be required for this if it occurs in childhood.

A proportion of boys with Becker Muscular Dystrophy are more severely affected and present in childhood with muscle cramps and reduced walking speed. Ankle contractures (shortening) can occur and requires stretching exercises and physiotherapy. Reduced walking speed is rarely that severe but these severely affected children may require a wheelchair or scooter to get around –evidence of loss of walking ability in Becker Muscular Dystrophy must always be received from the treating Consultant Neuromuscular Diseases Specialist.

Intelligence is usually in the normal range although a minority of boys have variable learning and behavioural difficulties. They are educated in mainstream schools with no difficulties and can enter most fields of employment on leaving school. However less physical jobs are recommended as physical strength is likely to deteriorate with age.

Indicators of severe functional restriction -:

Limb Girdle Muscular Dystrophy

There are many different types of this condition. The name of the condition describes its effects – muscle weakness affecting the large muscles around the pelvis and shoulder. In most types of this condition, problems with walking due to weakness of the muscles around the pelvis affecting the legs will be the main symptom. The general rule with these is that those that present in infancy are severe, those that present in childhood are usually moderate and those that present in adulthood are mild. Adult onset types include Types 1A, 1D, 1E, 1F – no disabling effects are anticipated during childhood.

Those that may occur during childhood are briefly described below:

Childhood onset

1. LGMD type 1B – weakness of the legs begins in early childhood and is followed some years later by weakness of the arms. Walking speed and distance may be reduced; the condition slowly gets worse until walking ability is lost. Cardiac involvement is common and a pacemaker is often inserted to prevent sudden cardiac death.

2. LGMD type 1C – weakness of the legs and arms occurs in early childhood and slowly gets worse. Muscle pain is a feature of this condition; contractures particularly of the hips and ankles are also common.

3. LGMD type 2A – causes weakness of the arms and legs with the first symptoms noted on average at 9 years of age. Muscle wasting may occur in childhood. This is a mild condition with no care or mobility needs anticipated during childhood. Muscle wasting commonly occurs later on. Loss of ambulation in this condition occurs on average at around 38 years of age.

4. LGMD type 2B – this type causes weakness of the legs much more than the arms and symptoms are first noted during childhood. This is a mild condition and no care or mobility needs would be anticipated during childhood.

5. LGMD types 2C, 2D, 2E AND 2F – these types may be severe with walking ability lost by age 10; alternatively walking ability may be maintained until late adulthood. Cardiomyopathy is common. As with all rare types, evidence from the treating neuromuscular specialist especially on prognosis of the individual child’s condition will be important.

6. LGMD type 2G – onset may be in early childhood or the teenage years. Foot-drop is a common problem and can be corrected by a walking splint. Young children will need help with this. The condition is slowly progressive and cardiomyopathy may occur. Needs are not anticipated except in young children who need help with splints or who have severe cardiomyopathy.

7. LGMD type 2H – onset in teenage or adult years. The symptom is muscle weakness but no needs are anticipated in the typical case.

8. LGMD type 2I and 2J– onset from childhood to adult – the progression of weakness is very variable– seek evidence on disabling effects from the neuromuscular specialist.

Facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy is named for the muscle groups it affects. These are the muscles of the face, shoulder and upper arm. The severity of the condition is related to age of onset, with the most severe cases developing symptoms in early childhood – severe cases with onset during childhood may be termed ‘infantile’ facioscapulohumeral muscular dystrophy in the medical evidence. The mild ‘adult onset’ form may be diagnosed from age 13 onwards. It will be important to confirm which type has been diagnosed and what the prognosis of the condition is from the treating specialist. The clinical features are as follows:

Emery-Dreifuss Muscular Dystrophy

The general rule with this type of muscular dystrophy is that those that present in infancy are severe, those that present in childhood are usually moderate and those that present in adulthood are mild. Children diagnosed in infancy are likely to have a severe condition and may never be able to walk or manage activities of daily living for themselves.

Those with onset during childhood may lose walking ability before they reach 16, others may never lose walking ability. In all cases information on the diagnosis and prognosis of the condition should be requested from the treating neuromuscular specialist. A feature of this condition is involvement of the heart. Heart failure and arrhythmias are the most common causes of death. Serious heart problems particularly arrhythmias may develop by the 30s in an otherwise mild case. Fitting a pace maker can be life saving. Survival depends on appropriate management of the heart condition.

Contractures (shortening) of tendons are common and these reduce joint movement. The joints most commonly affected are the elbow, ankle and back of the neck. These contractures can be treated surgically to maintain mobility and range of movement.

Congenital Muscular dystrophy (CMD) with protein laminin-A2 (LAMA2) deficiency – the condition is also known as MDC1A, Classic CMD or Merosin Deficient CMD

This is the most common form of congenital muscular dystrophy accounting for around 40% of congenital muscular dystrophy cases. As the name suggests this condition causes symptoms early in life and is often diagnosed before the age of one. The symptoms include any or all the following:

The diagnosis is made based on the clinical features, muscle biopsy and genetic testing. The majority of these children are very disabled by their muscle weakness and though most will learn to sit up they will rarely be able to stand or walk. Children with rare subtypes of this condition will learn to walk and self care. Evidence from the treating neuromuscular specialist on diagnosis and the prognosis of the child’s condition will be very important.

Ullrich Congenital Muscular Dystrophy

As the name suggests this condition causes symptoms early in life and is often diagnosed before the age of one. The symptoms include any or all the following:

The diagnosis is made based on the clinical features, muscle biopsy and genetic testing. Intelligence is normal in these children. The majority are very disabled by their muscle weakness; most of them will never walk due to muscle weakness and those that do tend to lose walking ability within 2-10 years of learning to walk.

Walker-Warburg Syndrome (a form of congenital muscular dystrophy)

This condition has all the features of the other types of congenital muscular dystrophy:

and

Indicators of severe functional restriction in rare types of muscular dystrophy – applies to all types

Diagnosis with:

Care and mobility considerations

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