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

## TL;DR

A 4-month-old boy with severe symptoms was diagnosed with ornithine transcarbamylase deficiency, a rare metabolic disorder, and stabilized with timely treatment.

## Contribution

This case highlights the importance of early ammonia testing and nitrogen-scavenging therapy in diagnosing and managing partial OTCD in resource-limited settings.

## Key findings

- Elevated ammonia and low citrulline levels indicated partial OTCD in a symptomatic infant.
- Nitrogen-scavenging therapy and dietary adjustments stabilized the patient without dialysis.
- Early diagnosis and treatment can prevent severe complications and improve outcomes in OTCD.

## Abstract

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.

Early ammonia testing is critical in infants with unexplained encephalopathy and sepsis‐like features. Hyperammonemia with low citrulline suggests partial OTCD. Prompt nitrogen scavengers and protein restriction can stabilize patients and avoid dialysis. Early diagnosis enables timely genetic counseling.