Paeds Vivas · genetics-dysmorphology-and-metabolism
Urea cycle disorders and hyperammonaemia — branching viva
Branching viva on the urea cycle disorders: recognising the neonatal and late-onset presentations of hyperammonaemia, localising the defect with plasma amino acids and urinary orotic acid, delivering the 'treat on suspicion' emergency protocol, and locking in long-term medical and transplant-based management with family counselling.
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Opening framework
My framework has four layers. First, the recognition — a well neonate deteriorating 24 to 72 hours into feeds with a respiratory alkalosis and encephalopathy is a urea cycle disorder until proven otherwise, and the ammonia is the test that decides it. Second, the emergency protocol — treat on suspicion: stop protein, calorie-load, scavenge nitrogen, give arginine, and dialyse at threshold. Third, the biochemistry — the cycle spans the mitochondrion and cytosol, and each block produces a recognisable metabolite pattern. Fourth, the family — an X-linked OTC diagnosis obliges carrier testing of the mother and sisters and reproductive counselling. [1]
References5ShowHide
- [1]Häberle J, Burlina A, Chakrapani A, Dixon M, et al. Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision. J Inherit Metab Dis, 2019.PMID 30982989
- [3]Brusilow SW, Maestri NE. Urea cycle disorders: diagnosis, pathophysiology, and therapy. Adv Pediatr, 1996.PMID 8794176
- [5]Raina R, Bedoyan JK, Lichter-Konecki U, Jouvet P, et al. Consensus guidelines for management of hyperammonaemia in paediatric patients receiving continuous kidney replacement therapy. Nat Rev Nephrol, 2020.PMID 32269302
- [10]García Vega M, Andrade JD, Morais A, et al. Urea cycle disorders and indications for liver transplantation. Front Pediatr, 2023.PMID 36937980
- [12]Lo RS, Cromie GA, Tang M, et al. The functional impact of 1,570 individual amino acid substitutions in human OTC. Am J Hum Genet, 2023.PMID 37146589