DESMIN PATHOLOGY IN NEUROMUSCULAR DISEASES

Desmin is an intermediate filament protein that in striated muscle is normally located at Z-bands, beneath the sarcolemma, and prominently a t neuromuscular junctions. It is abundant during myogenesis and in reg enerating fibers, but decreases in amount with maturation; in regenera ting and denervated muscle fibers it is co-expressed with vimentin. Ag gregates of desmin occur as nonspecific cytoplasmic bodies or cytoplas mic spheroid complexes, similar to the aggregates of keratin filaments in Mallory bodies or the neurofilament aggregates in Lewy bodies. In all three instances, alpha-B crystallin may be associated with desmin. There are now increasing numbers of neuromuscular disorders in which abnormal amounts of desmin, some abnormally phosphorylated, feature pr ominently in muscle fibres. Several of these diseases, including spher oid body myopathy, granulo-filamentous body myopathy and the dystrophi nopathies, are familial. Ultrastructural and immunohistochemical studi es of desmin have considerably broadened our understanding of the path ology of the cytoskeleton in muscle fibers and in certain hereditary n euromuscular diseases.