The most prevalent urea cycle disease is ornithine transcarbamylase deficiency (OTCD), which has an X-linked inheritance pattern. In male newborns, the classical type produces vomiting and lethargy in the neonatal period; if left untreated, severe hyperammonemia can induce acute neurotoxic consequences and lifelong impairment. OTCD can develop in heterozygous females as well, however the symptoms vary. The study presents two examples of female paediatric OTCD patients who presented with abrupt liver failure. Both patients had minimal oral intake at the time of presentation, which resulted in the lack of orotic aciduria, delaying the diagnosis. 

These examples highlight the need of considering urea cycle abnormalities in children presenting with acute liver failure, as well as the need to repeat the urine metabolic test with an unrestricted diet if there is a high clinical suspicion.