Ornithine Transcarbamylase (OTC) Deficiency

What this deck covers

Ornithine Transcarbamylase (OTC) Deficiency in fourteen clinical teaching cases with worked explanations. Each case gives you a clinical vignette, four options, the correct answer, and an explanation of why each of the other three is wrong.

Diagnoses and management options tested

Across the fourteen cases you are asked to choose between options such as: Neonatal sepsis, Hypoxic-ischaemic encephalopathy, Urea cycle disorder, Inborn error of fatty acid oxidation, Converts arginine to urea and ornithine, Converts argininosuccinate to arginine and fumarate, Autosomal recessive, Autosomal dominant, Mitochondrial inheritance, X-linked recessive, Plasma arginine level, Serum citrulline level, Urinary orotic acid, Liver OTC enzyme activity, High citrulline, high argininosuccinic acid, low arginine, High citrulline, high ammonia, low ornithine, Low glutamine, high arginine, high citrulline, OTC deficiency, Argininosuccinic aciduria (ASA), Citrullinemia type 1, CPS1 deficiency or NAGS deficiency, High-protein diet to prevent muscle catabolism, Sodium phenylbutyrate overdose, Dietary protein deficiency causing catabolism, Bacterial meningitis, Postpartum psychosis.

Clinical pearls from this deck

• A neonate with unexplained hyperammonemia, respiratory alkalosis, and a normal glucose has a urea cycle disorder until proven otherwise. Ammonia 890 µmol/L against a normal below 110 is an order of magnitude beyond what sepsis produces. Ammonia stimulates the respiratory centre → hyperventilation → pH 7.52.
• OTC is a mitochondrial enzyme of liver and intestinal mucosa that joins carbamoyl phosphate to ornithine to make citrulline. Block it and carbamoyl phosphate accumulates, escapes into the cytosol, and is diverted into pyrimidine synthesis → orotic aciduria. The downstream result is high glutamine, low citrulline, low arginine, and rising ammonia.

The fourteen worked cases in this deck, with the images and the full explanation of every option, are part of Pediatric Case Review membership. See what is included.

More from this system: all metabolic and genetic decks and question sets · pediatric reference values.