Abnormal expression of intermediate filament proteins in X-linked myotubular myopathy is not reproduced in vitro.

Expression patterns of the intermediate filament proteins (IFPs) desmin and vimentin, in biopsy material taken from a 1 day old boy with fatal neonatal X-linked myotubular myopathy (XLMTM) were compared with the expression of these proteins in cultured myotubes, from the same patient. Immunohistochemical studies revealed the persistence of high levels of desmin in virtually all, and vimentin in most, of the myofibres within the patient's biopsy. Analysis of intermediate filament expression in differentiating, cultured muscle cells did not reveal overt differences between XLMTM cultures and cultures of control muscle. Titin distribution patterns indicated a normal process of myofibrillogenesis in XLMTM myotubes. We conclude that the failure to properly regulate IFP-expression is not intrinsic to XLMTM muscle fibres. The possibility that this failure is due to a defective external, possibly neural factor, is discussed.