Muscle fibre type composition in distal myopathy (Welander). An analysis with enzyme- and immuno-histochemical, gel-electrophoretic and ultrastructural techniques.

The myopathic muscle of distal myopathy (Welander's disease), the dominantly inherited neuromuscular disorder which occurs frequently in Sweden, has been characterized by electron microscopy, enzyme- and immuno-histochemistry (using antibodies against embryonic, neonatal, fast and slow myosin, and against the muscle-specific intermediate filament protein, desmin), and with gel electrophoretic techniques. Of special interest is the fact that the ultrastructural appearance of the fibres with regard to M- and Z-band structures does not fit the proposed classification criteria for ultrastructural fibre typing of normal human muscle. Furthermore, contrary to previous results, we conclusively demonstrate that the predominating fibres are of a slow-twitch type. Unexpectedly, we also observed that embryonic and neonatal myosin was expressed in some residual fibres. This emphasises the importance of supplementing stains to demonstrate activity of ATPase with myosin immuno-histochemistry in order to improve understanding of fibre type characteristics in myopathic muscles. The origin of the myopathic muscle fibres in distal myopathy could not be definitely determined, but it is suggested that neurogenic disturbances play an important part in the pathophysiology of Welander's disease.