IMMUNOPHENOTYPING OF CONGENITAL MYOPATHIES - DISORGANIZATION OF SARCOMERIC, CYTOSKELETAL AND EXTRACELLULAR-MATRIX PROTEINS

We have studied the expression and distribution patterns of the interm ediate filament proteins desmin and vimentin, the sarcomere components titin, nebulin and myosin, the basement membrane constituents collage n type IV and laminin, and the reticular layer component collagen type VI in skeletal muscle of patients with ''classic'' congenital myopath ies (CM), using indirect immunofluorescence assays. In all biopsy spec imens obtained from patients with central core disease (CCD), nemaline myopathy (NM), X-linked myotubular myopathy (XLMTM) and centronuclear myopathy (CNM), disease-specific desmin disturbances were observed. V imentin was present in immature fibres in severe neonatal NM, and as s arcoplasmic aggregates in one case of CNM, while the amounts of viment in and embryonic myosin, observed in XLMTM, decreased with age of the patients. Abnormal expression of myosin isoforms was found in several CM biopsies, although the organization of myosin and other sarcomere c omponents was rarely disturbed. Basement membrane and reticular layer proteins were often prominently increased in severe cases of CM. We co nclude that (i) desmin is a marker for individual types of CM and migh t be used for diagnostic purposes; (ii) the expression patterns of the differentiation markers desmin, vimentin and embryonic myosin in XLMT M, point either to a postnatal muscle fibre maturation or to a variabl e time-point of maturational arrest in individual patients; (iii) the correlation between the distribution patterns of extracellular matrix proteins and clinical presentation points to a role of these proteins in pathophysiology of CM.