Late-onset ornithine transcarbamylase deficiency: An under recognized cause of metabolic encephalopathy

INTRODUCTION Ornithine transcarbamylase deficiency is the most common inherited disorder of the urea cycle, has a variable phenotype, and is caused by mutations in the OTC gene. We report three cases of ornithine transcarbamylase deficiency to illustrate the late-onset presentation of this disorder and provide strategies for diagnosis and treatment. The patients were maternal first cousins, presenting with hyperammonemia and obtundation. Urea cycle disorder was not initially suspected in the first patient, delaying diagnosis. RESULTS Sequencing of the OTC gene showed a novel missense mutation, c.563G > C (p.G188A). Numerous family members were found to carry this mutation, which shows a trend toward later onset. Each urea cycle disorder has its own unique pattern of biochemical abnormalities, which differ from non-metabolic causes of critical illness. CONCLUSION Regardless of age, clinical suspicion of a urea cycle disorder is important in encephalopathic patients to ensure quick diagnosis and definitive treatment of the underlying inborn error of metabolism.