Disorders of Fructose Metabolism

Essential fructosuria

  • Involves a defect in fructokinase. Autosomal recessive.
  • A benign, asymptomatic condition (fructokinase deficiency is kinder), since fructose is not trapped in cells. Hexokinase becomes 1° pathway for converting fructose to fructose-6-phosphate.
  • Symptoms: fructose appears in blood and urine.
  • Disorders of fructose metabolism cause milder symptoms than analogous disorders of galactose metabolism.

Hereditary fructose intolerance

  • Hereditary deficiency of aldolase B. Autosomal recessive.
  • Fructose-1-phosphate accumulates, causing a ↓ in available phosphate, which results in inhibition of glycogenolysis and gluconeogenesis. Symptoms present following consumption of fruit, juice, or honey. Urine dipstick will be ⊝ (tests for glucose only); reducing sugar can be detected in the urine (nonspecific test for inborn errors of carbohydrate metabolism).
  • Symptoms: hypoglycemia, jaundice, cirrhosis, vomiting.
  • Treatment: ↓ intake of both fructose and sucrose (glucose + fructose).

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