Muscular dystrophies are inherited, progressive muscle disorders resulting from defects in one or more genes needed for normal muscle structure and function; dystrophic changes (eg, muscle fiber necrosis and regeneration) are seen on biopsy specimens. Facioscapulohumeral dystrophy is the most common form of muscular dystrophy, and Duchenne dystrophy and Becker dystrophy are the second most common. Duchenne dystrophy is a more severe form; Becker dystrophy, although closely related to Duchenne, has a later onset and causes milder symptoms.
Muscular dystrophies are distinguished by the selective distribution of weakness and the specific nature of the genetic abnormality involved.
Inherited metabolic disorders affecting the muscles, such as mitochondrial oxidative phosphorylation disorders and glycogen storage diseases, are discussed elsewhere. Only those disorders that have all or most of their effects on muscle are discussed in this chapter.
Congenital muscular dystrophy is not a single disorder but instead refers to muscular dystrophy evident at birth or in infancy, occurring from any of several rare forms of muscular dystrophy. All such dystrophies are genetically recessive and result from mutations in a variety of different genes including those that encode for structural proteins of the basal membrane or the extracellular matrix of skeletal muscle fibers.
The diagnosis of congenital muscular dystrophy is suspected in any floppy neonate but must be distinguished from a congenital myopathy by muscle biopsy. Blood tests to evaluate muscle proteins, ultrasonography and magnetic resonance imaging of muscle, and genetic testing when available, are typically done to arrive at an accurate diagnosis.
No specific treatment exists for congenital muscular dystrophies. Orthopedic, cardiac, respiratory, nutritional, and social issues may be addressed by appropriate experts as the needs arise, and supportive care, including physical therapy helps preserve function.
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