Glycogen Storage Disease Type VII (GSD VII)

One of the four glycogen storage diseases characterized by phosphofructokinase deficiency in the muscles and associated with abnormal deposition of glycogen in muscle tissues, exercise intolerance, and anemia.

Muscle Phosphofructokinase Deficiency; Tarui Disease; Glycogenosis type VII.

Also named Tarui disease after the Japanese physician Seiichiro Tarui (born in 1927) who first described the disease in 1965.

Less than 50 cases reported (<10 for the infantile lethal form). This condition is mainly observed in the Ashkenazi Jewish people.

Autosomal recessive; however, more males than females have been reported. The gene causing GSD VII (M subunit gene) has been mapped to chromosome 1.

Deficiency of muscle phosphofructokinase, which catalyzes the irreversible conversion of fructose-6-phosphate to fructose-1,6-bisphosphate in glycolysis. As a consequence, free or glycogen-derived glucose cannot be used as a source of energy and glycogen accumulates because of impaired degradation and/or excess synthesis. Increased levels of glucose-6-phosphate activate the hexose monophosphate shunt, thus enhancing nucleotide formation and uric acid production. The enzymatic block also causes a decrease in 2,3-diphosphoglycerate (DPG). Oxygen affinity of hemoglobin is therefore increased, as is the production of new erythrocytes, resulting in compensated anemia.

Based on the clinical findings in patients with muscular exercise intolerance exacerbated by glucose infusion prior to exercise, fatigue, vomiting, muscle weakness, myalgia, cramps, and myoglobinuria. Phosphofructokinase deficient in skeletal muscle, but not in the liver. No rise in blood lactate concentration after ischemic exercise. Plasma creatine phosphokinase is increased. 31P-NMR spectroscopy reveals a specific peak of phosphorylated monoesters (accumulation of glycolytic intermediates resulting from the enzymatic block). A severe infantile form with arthrogryposis, cardiomyopathy, and frequent respiratory failure has been described. Death occurs early. Antenatal detection possible in families with identifiable mutations.

Clinical features similar to GSD type V. Temporary weakness and painful muscle cramps occur after exercise. Myoglobinuria may occur with extreme exertion. Patients tend to develop hemolytic anemia (with jaundice as a result of partial erythrocyte phosphofructokinase deficiency) and myogenic hyperuricemia.

Three clinical forms have been described: classic, infantile onset, and late onset type. The classic form includes exercise intolerance, fatigue, and myoglobinuria. The infantile form may include myopathy, mental retardation, cataracts, joint contractures, and death during childhood. The late-onset form consists of progressive muscle weakness developing in adults.

Assess history of muscle weakness. Monitor hemoglobin and reticulocyte count and renal function in cases of myoglobinuria. Perform ultrasonography to evaluate the presence of gallstones in case of hyperbilirubinemia. Evaluate cardiac and respiratory function if necessary, particularly in the infantile form (clinical aspects, radiographs, echocardiography, pulmonary function tests). Check renal function in the presence of myoglobinuria.

Tourniquets may precipitate painful muscle cramps. Maintain normothermia to prevent shivering in the postoperative period, which could trigger severe muscle cramps and myoglobinuria. Careful intraoperative positioning is needed in patients with myalgia and weakness. Postoperative ventilatory support can be necessary in severe forms.

Avoid succinylcholine. Use of nondepolarizing muscle relaxants should not cause problems, but should be administered with proper monitoring. Due to its metabolism, cis-atracurium seems to be the relaxant of choice. Propofol increases uric acid excretion and should probably be avoided for long-term infusion (total intravenous anesthesia, sedation). Effect of perioperative glucose infusion is unknown.

Other glycogen storage diseases.