McArdle disease: phosphorylase activity in regenerating muscle fibers.

Phosphorylase activity was found histochemically in regenerating muscle fibers in biopsied muscle from a patient with otherwise typical McArdle disease. Phosphorylase activity, shortly after episodes of muscle necrosis, was identified in this patient and in others reported in the literature. Detection of phosphorylase activity accompanied histologic evidence of regenerating muscle fibers and excessive glycogen accumulation. The biopsied muscle had virtually no biochemical enzyme activity. The present study supports a recently introduced hypothesis stating that in McArdle disease there is a lack of "mature" phosphorylase, but skeletal muscle cells are able to manufacture "fetal" phosphorylase isoenzyme during muscle regeneration.