Laboratory diagnosis of the neuromuscular glycogen storage diseases.

Of the 12 known genetic disorders of glycogen metabolism, five consistently involve the neuromuscular system. Pompe's disease is a generalized, fatal, lysosomal storage disease caused by absence of acid maltase. Structurally abnormal glycogen accumulates in Forbes-Cori and Andersen's diseases, resulting from deficient debranching and branching enzymes, respectively. Exercise intolerance, muscle cramps, and myoglobinuria characterize McArdle's syndrome or myophosphorylase deficiency. In Tauri's disease, absence of phosphofructokinase leads to glycogen accumulation indirectly owing to a metabolic block in glycolysis. Diagnosis of the symptomatic patient, antenatal diagnosis, and detection of heterozygous genetic carriers are accomplished using a variety of laboratory methods. Tissue enzyme assays, chemical analysis of glycogen, and studies of carbohydrate metabolism are available. Recent advances in biophysics, such as nuclear magnetic resonance, have opened up a new approach for the study of metabolic diseases.