A Complex Case of Ornithine Transcarbamylase Deficiency in a Patient With Severe Comorbid Conditions

Ornithine transcarbamylase deficiency (OTCD) is the most common urea-cycle disorder, but it is often overlooked in Pakistan. It can present after the neonatal period with symptoms resembling sepsis and significant respiratory alkalosis. We report a 4-month-old boy with fever, lethargy, poor feeding, and loose stools for 5 days. He arrived with a rapid heart rate and quick breathing. His arterial blood gas showed a pH of 7.65, pCO₂ of 14 mmHg, and HCO₃ ^- of 15.5 mmol/L. Plasma ammonia levels were elevated at 78.1 μmol/L (reference range 11-32). A quantitative amino acid test revealed greatly increased glutamate (263 μmol/L; reference range 18-98) with low citrulline (6 μmol/L; reference range 16-32) and a normal ornithine/arginine ratio, which matches the pattern seen in partial OTCD. A contrast-enhanced CT scan of the brain showed widespread leptomeningeal enhancement and mild enlargement of the bifronto-temporal subarachnoid spaces. An echocardiogram found a small secundum atrial septal defect (ASD) and a tiny patent ductus arteriosus (PDA), with normal function in both ventricles. The patient was treated for suspected sepsis and high ammonia levels using sodium benzoate, L-arginine, L-carnitine, micronutrient support, and a low-protein diet based on formula (Basic-P/Morinaga BF-1). This led to steady improvements in his clinical condition and blood work. This case highlights three key points for resource-limited settings: (i) check ammonia levels early in any infant with unexplained encephalopathy and respiratory alkalosis; (ii) a low-citrulline/normal-ornithine profile should prompt evaluation for OTCD, even with mild hyperammonemia; and (iii) starting nitrogen-scavenging therapy and adjusting dietary protein can prevent the need for dialysis. Documenting these presentations helps raise awareness in the region and emphasizes the importance of access to confirmatory molecular testing and family counseling when newborn screening is not available.