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 Facioscapulohumeral Muscular Dystrophy Facioscapulohumeral muscular dystrophy is the most prevalent type of muscular dystrophy. Most cases manifest by age 20. It is characterized by weakness of the facial muscles and shoulder girdle... read more is the most common form of muscular dystrophy, and Duchenne dystrophy and Becker dystrophy Duchenne Muscular Dystrophy and Becker Muscular Dystrophy Duchenne muscular dystrophy and Becker muscular dystrophy are X-linked recessive disorders characterized by progressive proximal muscle weakness caused by muscle fiber degeneration. Becker dystrophy... read more 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.
Other forms include Emery-Dreifuss dystrophy Emery-Dreifuss Dystrophy Emery-Dreifuss dystrophy is a muscular dystrophy with multiple modes of inheritance. In addition to weakness and muscle wasting, patients often have cardiac abnormalities that may cause sudden... read more , myotonic dystrophy Myotonic Dystrophy Myotonic dystrophy is rare and is autosomal dominant. Two types are recognized. Both affect voluntary muscles and one also affects involuntary muscles. Symptoms begin at adolescence or early... read more , limb-girdle dystrophy Limb-Girdle Dystrophy Limb-girdle dystrophy is a muscular dystrophy that has numerous subtypes; some are autosomal recessive and some are autosomal dominant. Time of onset is determined by the mode of inheritance... read more , oculopharyngeal muscular dystrophy, and congenital dystrophies Congenital Myopathies Congenital myopathy is a term sometimes applied to hundreds of distinct neuromuscular disorders that may be present at birth, but it is usually reserved for a group of rare, inherited, primary... read more .
Muscular dystrophies are distinguished by the selective distribution of weakness and the specific nature of the genetic abnormality involved.
Other inherited muscular disorders include congenital myopathies Congenital Myopathies Congenital myopathy is a term sometimes applied to hundreds of distinct neuromuscular disorders that may be present at birth, but it is usually reserved for a group of rare, inherited, primary... read more , myotonia congenita Myotonia Congenita Myotonia congenita is an inherited disorder causing muscle stiffness and hypertrophy beginning during childhood. There are 2 main types with different modes of inheritance and manifestations... read more , and familial periodic paralysis Familial Periodic Paralysis Familial periodic paralysis is a rare autosomal dominant condition with considerable variation in penetrance characterized by episodes of flaccid paralysis with loss of deep tendon reflexes... read more .
Inherited metabolic disorders Introduction to Inherited Disorders of Metabolism Most inherited disorders of metabolism (also called inborn errors of metabolism) are caused by mutations in genes that code for enzymes; enzyme deficiency or inactivity leads to Accumulation... read more affecting the muscles, such as mitochondrial oxidative phosphorylation disorders Mitochondrial Oxidative Phosphorylation Disorders Impairment of oxidative phosphorylation often, but not always, causes lactic acidosis, particularly affecting the central nervous system, retina, and muscle. See also Approach to the Patient... read more and glycogen storage diseases Glycogen Storage Diseases Glycogen storage diseases are carbohydrate metabolism disorders. There are many numbered and named types, all of which are caused by deficiencies of enzymes involved in glycogen synthesis or... read more , 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 Congenital Myopathies Congenital myopathy is a term sometimes applied to hundreds of distinct neuromuscular disorders that may be present at birth, but it is usually reserved for a group of rare, inherited, primary... read more 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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