Confocal analysis of the dystrophin protein complex in muscular dystrophy.

The dystrophin protein complex (DPC), composed of at least 10 proteins that associate with dystrophin, is critical for the maintenance of normal muscle fiber structure and physiology. In this study, we used immunohistochemistry and confocal microscopy to examine the relative abundance and distribution of several of these proteins in muscle biopsies taken from patients with various muscular dystrophies. The optical sectioning capability of confocal microscopy allowed us to comprehensively analyze the semiquantitative expression of components of the DPC. Alpha-sarcoglycan-deficient patients displayed a marked reduction in membrane immunostaining of the sarcoglycan complex. Gamma-sarcoglycan-deficient patients showed variable decreased immunostaining of the sarcoglycan complex proteins. When beta-sarcoglycan was expressed appropriately at the sarcolemma of gamma-sarcoglycan-deficient patients, intracellular labeling of beta-sarcoglycan was also present. Beta-sarcoglycan-deficient patients showed poor localization of extracellular matrix proteins in addition to a complete absence of the sarcoglycans. Merosin-deficient patients showed relatively normal immunostaining levels of all other members of the DPC. Finally, dystrophin-deficient patients showed little or no change in the expression of extracellular matrix proteins; however, some sarcoglycans were significantly decreased. These data allowed us to suggest unique fundamental interactions between the members of the DPC.

A novel ryanodine receptor gene mutation causing both cores and rods in congenital myopathy.

BACKGROUND: Central core disease (CCD) and nemaline rod myopathy are generally considered two genetically and histologically distinct disorders. CCD is defined by the presence of well-demarcated round cores within most myofibers. Nemaline rod myopathy is distinguished by the presence of characteristic nemaline bodies within myofibers. The simultaneous occurrence of both cores and rods in the same muscle biopsy has been described, but no gene mutations have been reported yet for this condition. OBJECTIVE: To describe a family containing 16 affected individuals in six generations with an autosomal dominant congenital myopathy that shows clinical and histologic features of both CCD and nemaline myopathy, and to determine the genetic etiology and protein composition of the cores/rods in this family. METHODS AND RESULTS: The results of linkage analyses excluded involvement of the two autosomal dominant nemaline myopathy loci on chromosome 1, but were consistent with a localization of the disease gene at the CCD locus on chromosome 19q13.1 (ryanodine receptor). SSCP analysis and DNA sequencing identified a novel Thr4637Ala mutation in the transmembrane region of the ryanodine receptor protein. Immunofluorescence studies of patient muscle biopsies showed the central cores to stain for ryanodine receptor. CONCLUSIONS: These data suggest that the occurrence of nemaline bodies can be a secondary feature of CCD, and that genetic studies on previously reported core/rod families should be targeted to the ryanodine receptor locus. The results of the immunofluorescence studies suggest that the cores contain excess abnormal ryanodine receptor protein.