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A review is presented of genetic defects affecting fructose metabolism in humans. Presently, six conditions have been recognized: fructose malabsorption, fructokinase deficiency, aldolase A and aldolase B deficiency, fructose-1,6-diphosphatase deficiency and D-glyceric aciduria. Clinical presentations of these conditions, enzymatic and/or molecular defects, pathophysiological consequences, and modes of treatments are discussed.
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Glucose carbon recycling, glucose production and glucose turnover in glycogen storage disease type I and type II patients and control subjects were determined by a novel approach--mass isotopomer analysis of plasma 13C glucose. Changes in the isotopomer distribution of plasma 13C glucose were found only in glycogen storage disease type III patients and control subjects. Glucose carbon recycling parameters were also derived from 13C NMR spectra of plasma glucose C-1 splitting pattern. Our results eliminate a mechanism for glucose production in glycogen storage disease type I children involving gluconeogenesis. However, glucose release by amylo-1,6-glucosidase activity is in agreement with our results. A quantitative determination of the metabolic pathways of fructose conversion to glucose in normal children, and in children with disorders of fructose metabolism was derived from 13C NMR measurement of plasma 13C glucose isotopomer populations following [U-13C]fructose administration. A direct pathway from fructose, bypassing fructose-1-phosphate aldolase, to fructose-1,6-diphosphate in controls and hereditary fructose intolerant children (47% and 27%, respectively) was identified. In children with fructose-1,6-diphosphatase deficiency, only the gluconeogenic substrates were 13C labelled but no synthesis of glucose from [U-13C]fructose occurred. The significantly lower (by 68%) conversion of fructose to glucose in hereditary fructose intolerance, as compared to control subjects, and non-conversion in fructose-1,6-diphosphatase deficient subjects after [U-13C]fructose (approximately 20 mg/kg) administration can serve as the basis of a safe diagnostic test for patients suspected of inborn errors of fructose metabolism and other defects involving gluconeogenesis.
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Three boys and one girl suffering from inherited fructose-1,6-diphosphatase (FDPase) deficiency are reported. All four patients had less than 25% residual hepatic FDPase activity. While in two out of three patients the enzyme deficiency was also expressed in leucocytes, one patient had a normal enzyme activity. Remarkably, three patients had pronounced neonatal hyperbilirubinaemia requiring exchange transfusion.
A seven months old infant presented with recurrent episodes of acidosis and hypoglycemia triggered by fasting and febrile infections. The diagnosis of fructose-1,6-diphosphatase deficiency was made by demonstrating the enzyme deficiency in a liver biopsy specimen. Fructose-1,6-diphosphatase is a key enzyme of gluconeogenesis. Fructose-1,6-diphosphatase deficiency results in hypoglycemia and lactic acidosis during episodes of fasting. Diagnosis is made preferably by liver biopsy. Treatment includes elimination of fructose and sucrose from the diet and avoidance of fasting. Acute attacks are treated by intravenous infusion of glucose and bicarbonate if necessary.
A neonate is described whose clinical condition rapidly and irreversibly deteriorated on day two. He developed a profound acidosis, hypoglycaemia and a shock-like syndrome. The infant was centrally cyanosed and had a systolic murmur from a moderately severe pulmonary valve stenosis and a small atrial septal defect. The overwhelming acidosis was inconsistent with the severity of the congenital heart defects and as no infection was found a metabolic cause was sought. Liver tissue obtained at autopsy shortly after death on day four, showed deficiencies of fructose-1, 6-biphosphatase and aldolase.
A novel 31P magnetic resonance spectroscopy procedure allows the estimation of absolute concentrations of certain phosphorus-containing compounds in liver. We have validated this approach by measuring ATP, phosphomonesters, and inorganic phosphate (Pi) during fasting and after an i.v. fructose bolus in healthy adults and in three adults with disorders of fructose metabolism and by comparing results with known metabolic concentrations measured chemically. During fasting, the ATP concentration averaged 2.7 +/- 0.3 (SD, n = 9) mmol/L, which, after due correction for other nucleoside triphosphates, was 2.1 mmol/L and corresponded well with known concentrations. Fructose-1-phosphate (F-1-P) could not be measured during fasting; its concentration after fructose was calculated from the difference of the phosphomonester signals before (2.9 +/- 0.2 mmol/L) and after fructose. Pi was 1.4 +/- 0.3 mmol/L and represented the one fourth of Pi visible in magnetic resonance spectra. In the three healthy controls after fructose (200 mg/kg, 20% solution, 2.5 min), the fructokinase-mediated increase of F-1-P was rapid, reaching 4.9 mmol/L within 3 min, whereas the uncorrected ATP decreased from 2.7 to 1.8 mmol/L and the Pi from 1.4 to 0.3 mmol/L. The subsequent decrease of F-1-P, mediated by fructaldolase, was accompanied by an overshooting rise of Pi to 2.7 mmol/L. In the patient with essential fructosuria, the concentrations of F-1-P, ATP, and Pi remained unchanged, confirming that fructokinase was indeed inactive. In the patient with hereditary fructose intolerance, initial metabolic changes were the same as in the controls, but baseline concentrations were not yet reestablished after 7 h, indicating weak fructaldolase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
In describing one case of congenital fructose 1,6-diphosphatase deficiency the Authors review the several clinical conditions giving problems of differential diagnosis. For certain diagnosis they underline the importance of liver biopsy, to dose the deficient enzyme directly in the liver tissue.