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Dysferlin is a muscle transmembrane protein which plays a role in membrane fusion events at the sarcolemma and also participates in membrane repair processes . Mutations in the dysferlin gene cause a variety of muscular dystrophies. The aim of our study was to evaluate the ultrustructural abnormalities in a large series of patients showing reduced immunohistochemical staining for dysferlin.
Muscle biopsies were examined from 24 patients. In 12 patients there was a complete absence of immunocytochemical staining for dysferlin, while the remaining 12 patients demonstrated partial reduction in staining. Muscle biopsies were examined by histology, immunocytochemistry and electron microscopy. At the ultrastructural level particular attention was given to detecting abnormalities at the sarcolemmal regions. These included the presence of vacuoles, discontinuities in the plasma membrane, as well as duplications of the basal lamina and papillary projections.
Twenty three out of the twenty four patients investigated had electron microscopic abnormalities in the sarcolemma. The most frequent finding in the muscle biopsies examined was the presence of subsarcolemmal vacuoles, followed by the appearance of discontinuities in the plasma membrane. The other two defects, namely duplication of the basal lamina and papillary projections occurred rarely.
In general all the above ultrastructural changes were more frequent in the muscle biopsies of patients showing a complete absence of immunocytochemical staining, for dysferlin.
The most notable ultrastructural abnormalities seen in the muscle biopsies, with dysferlin deficiency were the presence of small subsarcolemmal vacuoles and discontinuities in the plasma membrane consistent with the role of dysferlin in the maintenance of sarcolemmal integrity. The current study demonstrates the usefulness of electron microscopy in the investigation of patients suspected of dysferlin deficiency.