Table 2

Differential diagnosis and mechanism of primary and secondary hyperammonaemia (HA)11 79 81

Increased ammonia production
ConditionSuggested mechanism
 Exercise/seizures/traumaAMP deamination
 Gastric bypass/starvationIncreased protein catabolism
  GI haemorrhage
  Total parenteral nutrition
Excess protein/nitrogen load
 Infections with urease-producing bacteriaUrinary tract infection, with relevant organisms splitting urea to form ammonia
Decreased ammonia elimination
 Acute or chronic liver diseaseReduced urea cycle, glutamine synthesis; portosystemic shunt
 Urea cycle disorderEnzyme block or substrate transport affecting urea cycle
 Fatty acid disorder of oxidationLack of acetyl-CoA leading to reduced CPS1 activity
 Organic acidaemiaNAGS inhibition by relevant increased acid
 Carbonic anhydrase Va deficiencyLack of bicarb leading to reduced CPS1
 Mitochondrial disordersImpaired ATP production/substrate
 Ornithine aminotransferase deficiencyLack of ornithine affecting OTC, urea cycle defects
 Glutamine synthase deficiencyDecreased glutamine and hence ammonia clearance
 Lysinuric protein intoleranceLack of urea cycle ornithine and arginine
  • CPS1, carbamoylphosphate synthetase; GI, gastrointestinal ; NAGS, N-acetylglutamate synthetase; OTC, ornithine transcarbamylase.