Peak hyperammonemia and atypical acute liver failure: The eruption of an urea cycle disorder during hyperemesis gravidarum

Inborn urea cycle disorders are under-recognised metabolic causes of hyperammonemia in adults. A 28-year-old primigravida, seven weeks pregnant, affected by hyperemesis gravidarum developed acute liver injury (ALI) and then acute liver failure (ALF) in less than 48 h. Because the patient developed atypical features, especially mildly elevated aminotransferases contrasting with very high blood ammonia levels (281 μmol/L), concomitant with normal serum creatinine, an inborn error of metabolism was suspected. We performed emergency metabolic analyses, stopped all protein intake and started with intravenous (i.v.) high caloric intake, nitrogen scavenger drugs and haemodialysis. The neurological and hepatic status of the patient quickly improved together with normalisation of her ammonemia levels. High plasma glutamine and urinary orotic acid, alongside low plasma arginine, citrulline and ornithine were suggestive of an ornithine transcarbamylase deficiency, later confirmed by molecular analyses. Foetal sex was female, as determined by foetal DNA analysis in maternal blood, and foetal development was unremarkable throughout the pregnancy. Delivery was induced at 39 weeks with a close monitoring of ammonemia levels and i.v. perfusion of carbohydrates and lipids during labour and immediately post-partum to avoid hypercatabolism. Delivery was uneventful and the patient delivered a healthy female baby. Urea cycle disorders should be contemplated in non-jaundiced patients with ALI or ALF, severe hyperammonemia and normal serum creatinine regardless of serum aminotransferase levels. The prompt recognition of this rare condition and the rapid initiation of adequate metabolic therapy are mandatory to prevent irreversible neurological sequelae and to avoid liver transplantation.