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The muscular dystrophies are inherited myopathic disorders characterized by progressive muscle weakness and wasting. They are subdivided by mode of inheritance, age at onset, and clinical features, as shown in Table 246. In the Duchenne type,
The muscular dystrophies.
Age at Onset
Disorder Inheritance (years) Distribution Prognosis
Duchenne type X-linked recessive 15 Pelvic, then shoulder girdle; Rapid progression. Death within later, limb and respiratory about 15 years after onset.
Beckers X-linked recessive 525 Pelvic, then shoulder girdle. Slow progression. May have normal life span.
Limb-girdle (Erbs) Autosomal recessive (August 1030 Pelvic or shoulder girdle Variable severity and rate of sporadic or dominant) initially, with later spread to the progression. Possible severe disability in middle life.
Facioscapulohumeral Autosomal dominant Any age Face and shoulder girdle Slow progression. Minor initially; later, pelvic girdle and disability. Usually normal life span.
Distal Autosomal dominant 4060 Onset distally in extremities; Slow progression.
Proximal involvement later.
Ocular Autosomal dominant Any age External ocular muscles.
(may be recessive) (usually 530) May also be mild weakness of face, neck, and arms.
Oculopharyngeal Autosomal dominant Any age As in the ocular form but with dysphagia.
A genetic defect on the short arm of the X chromosome has been identified in Duchenne dystrophy. The affected gene codes for the protein dystrophin, which is markedly reduced or absent from the muscle of patients with the disease.