Glycogen storage disease VII is an autosomal recessive metabolic disorder characterized clinically by exercise intolerance, muscle cramping, exertional myopathy, and compensated hemolysis. Myoglobinuria may also occur. The deficiency of the muscle isoform of PFK results in a total and partial loss of muscle and red cell PFK activity, respectively. Raben and Sherman (1995) noted that not all patients with GSD VII seek medical care because in some cases it is a relatively mild disorder.

Elevation of red cell ATP levels is accompanied by elevated red cell pyruvate kinase activity and mild erythrocytosis. Red cell life span is slightly shortened. The patients in whom this trait was first described were asymptomatic (summary by Beutler et al., 1997).