The present report describes the histochemical and biochemical findings of biopsied muscles in a 26-year-old male with myophosphorylase deficiency. Histochemical analysis of the first biopsy specimen revealed that the phosphorylase activity was absent, corresponding to an absent band at 94,000 Da on the basis of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Histochemically the second biopsy specimen showed a partial phosphorylase activity of type 2B fibers, corresponding to a weakly staining band at 94,000 Da on the basis of SDS-PAGE. The present study supports the hypothesis that myophosphorylase deficiency is essentially a single gene disorder, characterized by absence or marked reduction of the myophosphorylase protein.

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