Myopathy associated with Type III glycogenosis

Abstract Skeletal muscle involvement in a patient with type III glycogenosis is described. Ischaemic exercise of the forearm failed to produce a rise in venous lactate levels. Muscle glycogen content was 6.2% wet weight. The glycogen extracted from muscle had short outer chains and was increased in its degree of branching. Electron-microscopically, myofibrils were sometimes disrupted and destroyed by the excessive deposition of glycogen granules. Gel electrophoretic analysis of the muscle structural proteins showed splitting of the myosin band with relative preservation of the other proteins; such changes are commonly observed in other myopathies.