Late‐onset ornithine transcarbamylase deficiency: a rare cause of recurrent abnormal behavior in adults

Background Ornithine transcarbamylase is an enzyme of the urea cycle, which produces urea from ammonia. Although ornithine transcarbamylase deficiency mainly occurs as a severe neonatal‐onset disease, a late‐onset form that could become symptomatic from infancy to adulthood is also known. Case presentation A 34‐year‐old man presented with sudden onset of abnormal behavior, lethargy, and hyperammonemia (108 µmol/L). He had recently increased daily protein intake, which suggested urea cycle disorder. After initiation of protein‐restricted diet and treatment with arginine and sodium phenylbutyrate, his symptoms resolved, along with a decrease in the ammonia level. An R40H(c.119G > A) mutation in the OTC gene was identified. Conclusion Awareness of adult onset ornithine transcarbamylase deficiency in a patient with acute psychiatric symptoms due to hyperammonemia is important.