Dystrophin-positive myotubes in innervated muscle cultures from Duchenne and Becker muscular dystrophy patients.

Nerve-muscle co-cultures from five Duchenne muscular dystrophy (DMD) patients and one Becker (BMD) patient, were studied by immunocytochemistry with antibodies against different portions of dystrophin. Four DMD patients had a deletion in the dystrophin gene. Some dystrophin-positive myotubes were detected in a few samples of all DMD cases. PCR amplification of exon 8 of the dystrophin gene ruled out a contamination from rat spinal cord during innervation. Our results in three DMD cases, may be explained by a clonal selection of dystrophin-positive fibers observed in muscle biopsies, while in the other two cases, a "frame-restoring" mutation might account for the presence of dystrophin-positive myotubes. The possible expression of "dystrophin-related protein" or dystrophin immature isoform was considered. In the BMD case an abnormal truncated dystrophin was found in innervated muscle cultures, as well as in muscle biopsy.