Occupational therapy and Duchenne muscular dystrophy - an introduction

The muscular dystrophies are a group of inherited diseases in which various genes controlling muscle function are defective. In certain types of muscular dystrophy the basic defect is already known. There are over 60 different neuromuscular conditions, varying widely in terms of severity, age of onset, type of muscle affected, pattern of genetic inheritance and their effect on life expectancy (1). The common features of the conditions are that they are:

• progressive
• muscle wasting
• disabling

At the time of writing there is no known cure or treatment, although significant advances in medical research are being made.

Muscular dystrophy affects 30,000 people in the UK, both adults and children. The most common and usually most severe form of muscular dystrophy is Duchenne muscular dystrophy.

Contents:

• How is Duchenne muscular dystrophy inherited?
• How does Duchenne muscular dystrophy affect people?

How is Duchenne muscular dystrophy inherited?

Duchenne muscular dystrophy is due to a mutation on the X chromosome and is inherited as an X-linked recessive condition (2).

The gene defect causes a deficiency in the protein dystrophin. Usually, only boys are affected; there is an incidence of 1 in 3500 live male births. In approximately two-thirds of all cases the mother carries the defective gene, but she is not usually affected by it herself; such women are carriers. Genetic counselling is important in helping family members to understand the implications of X-linked inheritance and to consider the options available.

How does Duchenne muscular dystrophy affect people?

Most affected boys show the first signs of mobility problems between the ages of one and three years. The symptoms may vary and include delayed walking, abnormal waddling gait, frequent falls, difficulty with stairs or running, reluctance to walk, toe walking, an inability to
hop, skip or jump, cramp in the legs (usually calves) and difficulty getting up from the floor, which is achieved using Gower’s manoeuvre. The boy turns on to all fours, and rises by pressing on his thighs and ‘walking’ his hands up his legs until he is able to extend his hips and back. There is often pseudo hypertrophy of the calf muscles and a waddling gait with a lordotic posture, which becomes more obvious as the condition progresses. Some boys may present with speech and language difficulties or global development delay. There may be a varying degree of intellectual impairment, which may be reflected in poor reading ability, comprehension and memory skills.

Weakness of the arms is a later symptom, but may be found on clinical examination at an earlier date. The distribution of muscle weakness in both upper and lower limbs is initially mainly proximal and symmetrical; as the condition progresses distal weakness develops.

Inability to walk, in the majority of boys, occurs between 8 and 12 years. Loss of ambulation is complicated by the development of joint contractures at the hip, knee and ankle, and spinal deformities; in addition, the elbow and wrist may be affected by contractures.

The prognosis is universally poor and although a few boys survive into their late 20s, the average age of death is approximately 19 years. The cause of death is usually respiratory failure, often following a chest infection, although approximately 10% die suddenly and unexpectedly of cardiac failure.

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