Fructosaemia: An Inborn Error of Fructose Metabolism

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Abstract
Three cases, two sibs and an infant of an unrelated family are described with fructosemia, an inherited disorder of fructose metabolism. A review of the 16 cases so far reported, including the present ones, shows that the younger age-group presents as failure to thrive, with vomiting and anorexia, hepatomegaly and hypoglycemic attacks, following weaning from the breast. The older age-group is often symptomless, but with a marked aversion to sweetened foods. It is concluded that the defect is inherited as an autosomal recessive trait. Measurements on a biopsy specimen of the liver from one of the three cases confirm that the underlying enzyme defect is an almost complete absence of liver aldolase activity to fructose-1-phosphate, with a markedly reduced activity to fructose-l:6-diphosphate. The effect of the anomaly on carbohydrate metabolism is discussed. The severe hypoglycemia found when fructose is ingested is not due to insulin response to high levels of fructose, but may result from the reduction in available intra-cellular phosphate by the accumulation of the blocked fructose-1-phos-phate. The ingestion of fructose results also in a decrease in the plasma phosphorus and an increase of plasma magnesium. It is postulated that both may be due to the consumption of ATP-Mg complex to form fructose-1-phosphate, ADP and free magnesium. The depletion of ATP, it is suggested, may be responsible for some general cellular disturbances and toxic manifestations. Similar changes were found after oral galactose in two cases of galactosemia, and the clinical and biochemical similarity and the differentiation between this condition and fructosemia are discussed.