Early onset myophosphorylase deficiency (Mc Ardle's disease) with absence of myophosphorylase protein on SDS electrophoresis. The role of the ischemic forearm test.

The authors present a case report of early onset myophosphorylase deficiency (Mc Ardle's disease) with absence of myophosphorylase protein on SDS-electrophoresis. The different varieties of myophosphorylase deficiency and the clinical investigations which may lead to the diagnosis are reviewed. In particular, the relevance and possible dangers of an ischemic forearm exercise test and the suggestion of using a needle biopsy as a preliminary screening in similar cases of metabolic myopathies are discussed.