DYSTROPHIN EXPRESSION AND SOMATIC REVERSION IN PREDNISONE-TREATED AND UNTREATED DUCHENNE DYSTROPHY

The mechanism by which prednisone improves muscle strength and function in Duchenne muscular dystrophy (DMD) is unknown. We addressed the possibility that clinical improvement was related to prednisone-induced alterations in skeletal muscle dystrophin. We performed muscle biopsies on patients at the conclusion of a randomized, double-blind, 6-month trial of prednisone and analyzed dystrophin content using Western blots and antibody staining of tissue sections. These studies demonstrated no significant differences in dystrophin content between treatment (prednisone 1.5 mg/kg/d, n = 12; prednisone 0.75 mg/kg/d, n = 9) and placebo (n = 12) groups. Of interest, however, was the presence of varying numbers of dystrophin-positive fibers (revertants) occurring individually or in clusters in antibody-stained tissue sections of more than one-half of the Duchenne patients. Mutation analysis revealed that revertants occurred in DMD patients with identifiable deletions or duplications, and in nondeletion patients. Prednisone treatment did not influence the prevalence of revertants. Revertants are most likely due to a second-site mutation occurring in a somatic cell allowing for restoration of the translational reading frame of the dystrophin transcript.