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Ornithine Transcarbamylase Deficiency — RACP Paediatrics MCQ

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HardGenetics & MetabolicOrnithine Transcarbamylase DeficiencyRACP Paediatrics

A 2-day-old neonate presents with poor feeding, vomiting, lethargy, and hyperammonaemia (ammonia 800 μmol/L). Blood gas shows respiratory alkalosis. Plasma amino acids show elevated glutamine and low citrulline. What is the most likely diagnosis?

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Correct answer: B — Ornithine transcarbamylase (OTC) deficiency

Severe neonatal hyperammonaemia with respiratory alkalosis, elevated glutamine and low citrulline points to a urea cycle defect. Ornithine transcarbamylase (OTC) deficiency is the most common urea cycle disorder (X-linked). In proximal urea cycle defects, citrulline is low. Emergency management includes IV sodium benzoate and sodium phenylacetate (ammonia scavengers), protein restriction, and consideration of haemodialysis for severe hyperammonaemia.

Reference: RACP – 2024 – Paediatric Curriculum: Metabolic Medicine