A group of rare inherited muscle disorders which cause slow, progressive wasting away of muscle fibres. This degeneration may lead to disability and death. The most common and severe form of muscular dystrophy is Duchenne muscular dystrophy. This is caused by a recessive gene carried on the X chromosome (see sex-linked inheritance). Boys only have one X chromosome, so if they inherit a copy of the defective gene from their mother they develop the disorder. Girls (with two X chromosomes) are not affected but become carriers of the defective gene. Affected boys walk with a waddle, find climbing difficult, and may have curvature of the spine. The disorder progresses rapidly: the ability to walk is lost by the age of 12, and few boys survive beyond the teenage years. Becker’s muscular dystrophy starts later in childhood and progresses more slowly. Myotonic dystrophy affects the muscles of the hands, face, neck, and feet, and causes learning difficulties. Limb-girdle muscular dystrophy mainly affects muscles in the hips and shoulders, and facioscapulohumeral muscular dystrophy affects muscles in the upper arms, shoulder girdle, and face. In this last form, severe disability is rare. A diagnosis for Duchenne muscular dystrophy can be made with gene testing before symptoms develop. Once muscle weakness develops other tests become useful, including measurement of muscle enzymes and an EMG. There is no cure, and physiotherapy is the main treatment. Remaining as active as possible keeps healthy muscles in good condition. Surgery to the heel tendons may assist walking in some cases. The long-term outlook depends on the particular form. Families in which a child or adult has developed any form of muscular dystrophy should receive genetic counselling.
Muscular dystrophy |
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