A previously healthy 18-month-old develops vomiting, sweating, tremor, and hypoglycemia 30 minutes after drinking apple juice. Urinalysis shows a positive Benedict test with negative glucose oxidase test. Between episodes the child is completely well. Intravenous fructose tolerance testing reproduces severe hypoglycemia with hypophosphatemia. What is the underlying defect?

• A Deficiency of fructose-1,6-bisphosphatase
• B Deficiency of fructokinase in liver
• C Deficiency of galactose-1-phosphate uridyltransferase
• D Deficiency of aldolase B in liver, kidney, and intestine ✓

Explanation

Hereditary fructose intolerance arises from aldolase B deficiency. Fructose-1-phosphate accumulates after fructose ingestion, trapping phosphate, depleting ATP, and secondarily inhibiting glycogenolysis and gluconeogenesis, hence acute hypoglycemia with hypophosphatemia and vomiting. Essential fructosuria (fructokinase deficiency) is asymptomatic with benign urinary fructose loss, which is why the symptomatic episodes exclude option B. Galactosemia presents with neonatal onset and cataracts rather than purely fruit-triggered attacks.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.