A Young Man with Late-onset Ornithine Transcarbamylase Deficiency Successfully Treated with Prompt and Intensive Blood Purification Therapy for Severe Hyperammonemic Encephalopathy

Ornithine transcarbamylase deficiency (OTCD) is a disorder of the urea cycle. A 19-year-old man with no medical or family history presented with sudden alterations in mentation after weight training and increased protein intake. His plasma ammonia level increased to >235 μmol/L, and intensive blood purification therapy was promptly initiated based on the assumption of acute hyperammonemic encephalopathy due to late-onset OTCD. On day 5, his mental status and plasma ammonia levels normalized, allowing discontinuation of blood purification therapy. An amino acid analysis confirmed the presence of OTCD. Prompt and intensive blood purification therapy is necessary to treat hyperammonemic encephalopathy due to late-onset OTCD.