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Disorder of fructose metabolism
Medical expert of the article
Last reviewed: 07.07.2025
Fructose-1-phosphate aldolase (aldolase B) deficiency
Deficiency of this enzyme results in the clinical syndrome of congenital fructose intolerance. The inheritance pattern is autosomal recessive; the incidence is estimated at 1/20,000 births. The child is healthy until he or she ingests fructose; then fructose-1-phosphate accumulates, causing hypoglycemia, nausea and vomiting, abdominal pain, sweating, tremor, confusion, drowsiness, seizures, and coma. Long-term fructose ingestion can lead to cirrhosis, mental retardation, and proximal renal tubular acidosis with loss of phosphate and glucose in the urine.
The diagnosis is suggested by symptoms in combination with recent fructose ingestion, and confirmed by liver enzyme testing or induction of hypoglycemia with intravenous infusion of fructose 200 mg/kg.
Diagnosis and identification of heterozygous carriers of the mutant gene can also be made using direct DNA testing. Acute therapy includes glucose administration to treat hypoglycemia; fructose, sucrose, and sorbitol must be excluded from the diet at all times. Many patients eventually develop an aversion to fructose-containing foods. The prognosis is excellent with treatment.
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Fructokinase deficiency
Deficiency of this enzyme causes a benign increase in fructose levels in the blood and urine (benign fructosuria). The inheritance pattern is autosomal recessive; the incidence is approximately 1/130,000 births. The condition is asymptomatic and is diagnosed incidentally by detecting reducing substances other than glucose in the urine.
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Fructose 1,6-biphosphatase deficiency
When this enzyme is deficient, gluconeogenesis is impaired, resulting in hypoglycemia, ketosis, and acidosis during starvation. This disease can be fatal in the neonatal period. The inheritance pattern is autosomal recessive; the frequency is unknown. Diseases that occur with an increase in body temperature to febrile numbers can provoke episodes. In the acute period, treatment includes the administration of glucose orally or intravenously. Tolerance to fasting usually improves with age.