Congenital Myopathies and Related Diseases

Abstract

Congenital myopathies (CM) are a gamut of clinicopathologically and genetically distinct disorders characterized by early-onset hypotonia and muscle weakness and inherited in autosomal dominant, recessive, or X-linked manner. Sometimes sporadic forms are seen. Respiratory muscle weakness is often severe and out of proportion to that of limb muscle weakness. Serum CK levels are usually within normal limits. The pathological abnormality common to most of the CM is the presence of hypotrophic type 1 fibers expressing slow myosin, which may sometimes be the only abnormality. Additional pathological features may include cytoplasmic bodies, nemaline rods, cores, tubular aggregates, central nuclei, caps, etc. Muscle biopsies can also show more than one of the aforementioned findings. There is a very high rate of phenotypic variability and genetic heterogeneity with respect to congenital myopathies [1]. Myocyte necrosis and endomysial fibrosis are rare features and when present prompt alternative diagnosis. The categories of CM are broad and encompass several entities, and discussing each detailed is beyond the scope of this chapter. Only the common CM are discussed, and the readers are requested to refer dedicated papers on individual CM.