Fructose 1,6-Diphosphatase Deficiency

Updated: Nov 03, 2015
  • Author: Sunil Kumar Sinha, MD; Chief Editor: Maria Descartes, MD  more...
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Overview

Background

Glucose homeostasis is essential for life. Because most of an organism's life is spent in a fasting state (ie, between meals), no fewer than 3 major mechanisms have evolved to maintain glucose homeostasis during a fast. These mechanisms are gluconeogenesis, glycogenolysis, and lipolysis.

In the immediate postprandial period, glycogenolysis represents the major homeostatic process to maintain euglycemia. In neonates, gluconeogenesis is particularly important for maintaining euglycemia. Fructose 1,6-diphosphatase (FDPase) (also termed fructose 1,6-bisphosphatase) is a focal enzyme in gluconeogenesis via its conversion of fructose 1,6-diphosphate (FDP) to fructose 6-phosphate (F-6-P), which permits endogenous glucose production from gluconeogenic amino acids (eg, alanine and glycine), glycerol, or lactate.

Deficiency of hepatic FDPase was first confirmed in 1970 by Baker and Winegrad. [1] They reported the dramatic clinical picture of acidosis in response to D-fructose challenge.

Of broader clinical interest, excess hepatic FDPase action contributes to hyperglycemia in patients with type 2 diabetes. The development of specific FDPase inhibitors has opened a novel avenue for treating patients with type 2 diabetes.

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Pathophysiology

FDPase catalyzes the conversion of FDP to F-6-P, which is a central step in gluconeogenesis. When challenged with D-fructose, patients lacking FDPase accumulate intrahepatocellular FDP, which inhibits gluconeogenesis and, if intracellular phosphate stores are depleted, inhibits glycogenolysis. The inability to convert lactic acid or glycerol into glucose leads to hypoglycemia, lactic acidosis, and glyceroluria.

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Epidemiology

Frequency

International

Incidence is approximately 1 in 20,000 live births worldwide.

Mortality/Morbidity

Patients develop severe hypoglycemia with metabolic acidosis upon ingestion of fructose. Fatal hepatic or renal injury following ingestion of fructose has been reported in these patients.

Early diagnosis of this disorder allows clinicians to advise patients regarding the avoidance of prolonged fasting and to initiate administration of intravenous dextrose promptly during illnesses associated with inadequate dextrose absorption (eg, vomiting or severe diarrhea).

Sex

Males and females appear to be affected in equal numbers.

Age

Patients with FDPase deficiency typically present in the newborn period with symptoms or signs related to hypoglycemia and metabolic acidosis following ingestion of fructose.

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