McArdle's disease: a study on the molecular basis of two different etiologies of myophosphorylase deficiency.

Three patients with myophosphorylase deficiency were investigated. Two had no detectable activity, while one had 1% residual activity. The patient with 1% residual activity had 40% of the normal amount of myophosphorylase protein. No myophosphorylase protein could be detected in the other two cases. A precipitin band in the Ouchterlony double immunodiffusion test was not present in any case. This study showed that modifying the normal enzyme (without changing the molecular weight) changed the immunoprecipitin activity of the phosphorylase protein. Therefore, immunoprecipitation is not a valid technique for differentiation of the variants of myophosphorylase deficiency, and another method, for example SDS-electrophoresis, should be applied.