Late-Onset Type of Skeletal-Muscle Phosphorylase Deficiency

A DISEASE attributed to a defect of glycogen breakdown in skeletal muscle was originally described by McArdle.1 It was subsequently found that in similarly affected patients skeletal-muscle phosphorylase was completely absent whereas the hepatic phosphorylase remained normal.2 , 3 In 2 patients the skeletal-muscle glycogen content was elevated,2 , 3 but it was normal in a third patient.4 One patient had proved myoglobinuria.2 Because venous-blood lactate failed to rise after exercise of an ischemic forearm in each case this test has been used to screen patients suspected of having this disease. All the patients previously studied had symptoms beginning in childhood that followed three . . .