Muscular dystrophies: an update on pathology and diagnosis.

Muscular dystrophies are clinically, genetically, and molecularly a heterogeneous group of neuromuscular disorders. Considerable advances have been made in recent years in the identification of causative genes, the differentiation of the different forms and in broadening the understanding of pathogenesis. Muscle pathology has an important role in these aspects, but correlation of the pathology with clinical phenotype is essential. Immunohistochemistry has a major role in differential diagnosis, particularly in recessive forms where an absence or reduction in protein expression can be detected. Several muscular dystrophies are caused by defects in genes encoding sarcolemmal proteins, several of which are known to interact. Others are caused by defects in nuclear membrane proteins or enzymes. Assessment of both primary and secondary abnormalities in protein expression is useful, in particular the hypoglycosylation of alpha-dystroglycan. In dominantly inherited muscular dystrophies it is rarely possible to detect a change in the expression of the primary defective protein; an exception to this is caveolin-3.