Myogenic Hyperuricemia

To identify the mechanism of hyperuricemia in glycogen storage diseases (glycogenoses) that affect muscle, we studied the effects of exercise and prolonged rest on purine metabolism in two patients with glycogenosis type III (debrancher deficiency), one patient with type V (muscle phosphorylase deficiency), and one patient with type VII (muscle phosphofructokinase deficiency). All had hyperuricemia except for one patient with glycogenosis type III. Plasma concentrations of ammonia, inosine, and hypoxanthine increased markedly in all the patients after mild leg exercise on a bicycle ergometer. The plasma urate concentrations also increased, but with a delayed response. Urinary excretion of inosine, hypoxanthine, and urate increased greatly after exercise, consistently with the increases in plasma levels. Hypoxanthine and urate concentrations were extremely high in the plasma and urine of the patient with glycogenosis type VII. With bed rest, the plasma hypoxanthine level returned to normal within a few hours, and the plasma urate concentration decreased from 18.6 to 10.6 mg per deciliter (1106 to 630 μmol per liter) within 48 hours. Similarly, the urinary excretion of these purine metabolites was reduced by bed rest. These findings indicate that muscular exertion in patients with glycogenosis types III, V, and VII causes excessive increases in blood ammonia, inosine, and hypoxanthine due to accelerated degradation of muscle purine nucleotides. These purine metabolites subsequently serve as substrates for the synthesis of uric acid, leading to hyperuricemia. (N Engl J Med 1987; 317: 75–80.), INVESTIGATIONS of inborn errors of metabolism have often contributed to our understanding of the biochemical basis for physiologic and pathophysiologic responses in human beings. Hyperuricemia is known to occur in glycogen storage disease (glycogenosis) type I (glucose-6-phosphatase deficiency, von Gierke's disease, or hepatorenal glycogenosis).¹ Overproduction of uric acid due to enhanced breakdown of ATP in the liver,^{2 3 4 5} and decreased renal excretion of urate due to lactic acidemia and ketonemia^6,7 are considered to be responsible for the hyperuricemia. According to recent reports,^{8 9 10 11 12 13 14} hyperuricemia or gout develops in a different manner in glycogenosis type VII (muscle phosphofructokinase deficiency, or Tarui's disease). Hyperuricemia…