Fatal Late-Onset Ornithine Transcarbamylase Deficiency in an Adolescent: A Case Report

The late-onset phenotype represents the most prevalent form of ornithine transcarbamylase (OTC) deficiency and is characterized by marked clinical heterogeneity, with disease onset ranging from early infancy to adulthood. We describe the case of a 12-year-old female with no significant past medical history who presented to the Emergency Department with an impaired level of consciousness and profound hyperammonemia (plasma ammonia: 432 μg/dL, and impairment of consciousness). Despite early initiation of continuous renal replacement therapy and aggressive management of cerebral edema, the patient developed refractory neurological deterioration and died five days after presentation. This case highlights that the late-onset form of OTC deficiency may manifest with severe neurological involvement and may be life-threatening. Timely recognition and aggressive management of hyperammonemia and impending hyperammonemic coma are essential to achieve improved clinical outcomes.