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The term “congenital myopathy” was originally used to describe a group of myopathic disorders presenting preferentially, but not exclusively, at birth and being morphologically distinct from congenital muscular dystrophies (Table 28-1).13 However, disorders that were once considered forms of muscular dystrophy are now known to be allelic to some types of congenital myopathy. For example, congenital muscular dystrophy with rigid spine syndrome, multi/minicore, and some cases of myofibrillar myopathy are caused by selenoprotein N1 mutations; sarcotubular myopathy and limb-girdle muscular dystrophy 2H (LGMD2H) are due to mutations in TRIM32; reducing body myopathy is now considered a type of LGMD. In addition, some disorders caused by mutations in sarcomeric proteins are classified as forms of LGMD (e.g., titinopathies, myotilinopathies, ZASPopathies), while others (e.g., actinomyosin, tropomyosin, α-actin, and troponin) are forms of congenital myopathy (nemaline myopathy). Thus, the nosology of what distinguishes a “congenital myopathy” from a “muscular dystrophy” on clinical and histopathologic grounds is not at all clear.

Usually, the congenital myopathies present in infancy as generalized hypotonia and weakness. Motor milestones are typically delayed. Affected infants are usually hypotonic and display delayed motor development. Some disorders with mutations in similar genes present later in childhood or even in adulthood. The congenital myopathies were initially considered as nonprogressive, although it is now clear that progressive weakness can occur.

Congenital myopathies can be inherited in an autosomal-dominant, autosomal-recessive, or X-linked pattern. Within families, there can be considerable variation with respect to disease presentation and degree of muscle involvement. The serum creatine kinase (CK) levels are either normal or usually mildly elevated. The classification of congenital myopathies has been based almost exclusively on clinical presentation and light/electron microscopic structural alterations of the muscle biopsy specimen (Table 28-1).


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