skip to main content

OTC deficiency – sodium benzoate — RACP Paediatrics MCQ

Instant feedback + full explanation. One question, done properly.

HardGeneticsOTC deficiency – sodium benzoateRACP Paediatrics

A 3-day-old neonate becomes acutely encephalopathic with seizures. Ammonia is 1200 µmol/L. Blood gas shows respiratory alkalosis. Amino acid profile shows elevated glutamine. Urine orotic acid is markedly elevated. What is the most likely diagnosis and what specific treatment should be given?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — IV sodium benzoate

Severe hyperammonaemia with respiratory alkalosis, elevated glutamine, and elevated urinary orotic acid in a neonate points to a urea cycle defect (orotic acid elevation specifically suggests OTC deficiency). Emergency management includes stopping protein, IV dextrose (to suppress catabolism), and IV nitrogen scavenger therapy (sodium benzoate and/or sodium phenylbutyrate). Haemodialysis/haemofiltration is needed for ammonia >500 µmol/L.

Reference: RCH Melbourne – 2023 – Metabolic Emergency CPG; RACP Paediatric Curriculum – Metabolic