Hereditary fructose intolerance vs Essential fructosuria
How to tell Hereditary fructose intolerance and Essential fructosuria apart when a board question makes them look alike.
Hereditary fructose intolerance is aldolase B toxicity with hypoglycemia; essential fructosuria is benign fructokinase loss.
Side by side
Hereditary fructose intolerance causes vomiting, lethargy, hypoglycemia, jaundice, liver dysfunction, and renal injury after fructose/sucrose ingestion from aldolase B deficiency.
Essential fructosuria is benign fructokinase deficiency causing fructose in urine without hypoglycemia, liver failure, or serious symptoms.
Aldolase B deficiency traps fructose-1-phosphate, depleting phosphate and inhibiting glycogenolysis and gluconeogenesis.
Fructokinase deficiency prevents fructose phosphorylation, so fructose is excreted without toxic phosphate trapping.
Hypoglycemia after fruit/juice, elevated fructose-1-phosphate, and liver injury support hereditary fructose intolerance.
Positive reducing sugar with benign course and no post-fructose hypoglycemia supports essential fructosuria.
The trap
Both involve fructose and reducing sugar, but only aldolase B deficiency makes a sick hypoglycemic child.
The repair move
For fructose disorders, ask whether fructose exposure makes the patient clinically ill and hypoglycemic.
Try a free question
CoreA 9-month-old infant develops vomiting, tremor, jaundice, and hypoglycemia (glucose 38 mg/dL) within an hour of being given apple juice and fruit puree. He is fine when only breastfed. Liver enzymes are markedly elevated. Which enzyme is deficient?
Show answer and explanation
Answer: A. Aldolase B (hereditary fructose intolerance). Hereditary fructose intolerance is aldolase B deficiency; fructose-1-phosphate is trapped, depleting cellular phosphate and ATP, which inhibits glycogenolysis and gluconeogenesis, producing fructose-induced hypoglycemia, liver injury, and vomiting.
Why the other choices are tempting
- B. Fructokinase deficiency (essential fructosuria) is BENIGN with no hypoglycemia or liver injury after fructose.
- C. GALT deficiency (classic galactosemia) is triggered by milk/galactose, not by fructose.
- D. Glucose-6-phosphatase deficiency (Von Gierke) causes fasting hypoglycemia independent of fructose intake.
- E. Phenylalanine hydroxylase deficiency (PKU) causes intellectual disability, not acute fructose-triggered hypoglycemia.
Flashcards
Tap a card to flip it.
What clue supports Hereditary fructose intolerance?
Choose Hereditary fructose intolerance when the stem gives this pattern: Hereditary fructose intolerance causes vomiting, lethargy, hypoglycemia, jaundice, liver dysfunction, and renal injury after fructose/sucrose ingestion from aldolase B deficiency.
What clue supports Essential fructosuria?
Choose Essential fructosuria when the stem gives this contrasting pattern: Essential fructosuria is benign fructokinase deficiency causing fructose in urine without hypoglycemia, liver failure, or serious symptoms.
Quick answers
What is the fastest way to tell Hereditary fructose intolerance from Essential fructosuria?
Hereditary fructose intolerance is aldolase B toxicity with hypoglycemia; essential fructosuria is benign fructokinase loss.
What is the key clue for Hereditary fructose intolerance?
Hereditary fructose intolerance causes vomiting, lethargy, hypoglycemia, jaundice, liver dysfunction, and renal injury after fructose/sucrose ingestion from aldolase B deficiency.
What is the key clue for Essential fructosuria?
Essential fructosuria is benign fructokinase deficiency causing fructose in urine without hypoglycemia, liver failure, or serious symptoms.
What is the common trap with Hereditary fructose intolerance vs Essential fructosuria?
Both involve fructose and reducing sugar, but only aldolase B deficiency makes a sick hypoglycemic child.