ABSENCE OF DYSTROPHIN AND SPECTRIN IN REGENERATING MUSCLE-FIBERS FROMBECKER DYSTROPHY PATIENTS

We studied muscle biopsies from 36 Becker muscular dystrophy patients, and correlated dystrophin negative fibers with regenerating and degen erating myofibers. Dystrophin immunohistochemistry was used to identif y dystrophin-negative and dystrophin-positive fibers. Immunohistochemi cal staining for fetal myosin and acid ATPase identified regenerating fibers, and calcium glioxalate and beta-spectrin staining identified n ecrotic fibers. All Becker biopsies contained detectable dystrophin in the majority of muscle fibers. 13 cases (36%) showed no dystrophin ne gative fibers, 9 cases (25%) showed a generalized, markedly decreased immunostaining pattern, and 14 cases (39%) showed a subset of dystroph in negative fibers (0.3-8% of total). Most dystrophin-negative fibers in Becker muscle were judged to be in the process of regeneration, and not in degeneration. No correlation was observed between the age of t he patients and number of dystrophin negative fibers. We conclude that the absence of dystrophin and spectrin labeling in some BMD myofibers is associated with regeneration, probably due to incomplete expressio n of dystrophin secondary to myofibers immaturity. Our results might b e explained by a developmental delayed expression of these two protein s, or by abnormal assembling in membrane's components during regenerat ion in dystrophy. Furthermore, our results rationalize the recently re ported finding of some dystrophin-negative fibers in polymyositis.