A full-term male neonate becomes lethargic and vomits on day 4 of life after initiation of formula feeds, progressing to seizures and coma. Plasma ammonia is 950 micromol/L, blood pH is 7.50, serum sodium and glucose are normal, and urinary orotic acid is markedly elevated. Blood urea nitrogen is very low. What is the most likely diagnosis?
- A Ornithine transcarbamylase deficiency ✓
- B Propionic acidaemia
- C Maple syrup urine disease
- D Non-ketotic hyperglycinaemia
Explanation
Ornithine transcarbamylase deficiency, the commonest urea cycle disorder and the only one that is X-linked, presents in affected boys with neonatal hyperammonaemic coma after protein introduction. Respiratory alkalosis from hyperventilation, low BUN, and markedly elevated urinary orotic acid (from accumulated carbamoyl phosphate spilling into the pyrimidine pathway) are characteristic. Organic acidaemias like propionic acidaemia produce metabolic acidosis with ketones, maple syrup urine disease shows branched-chain aminoaciduria, and non-ketotic hyperglycinaemia features raised CSF glycine.
Reference: Nelson Textbook of Pediatrics, 22nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.