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Abstract: SA-PO367

Fatal Hyperammonemia due to an Underlying Urea Cycle Disorder Unmasked by a High-Protein, Ketogenic Diet

Session Information

Category: Trainee Case Report

  • 1300 Health Maintenance, Nutrition, and Metabolism


  • Sourial, Mina, Montefiore Medical Center, Bronx, New York, United States
  • Sourial, Maryanne, Montefiore Medical Center, Bronx, New York, United States
  • Fisher, Molly, Montefiore Medical Center, Bronx, New York, United States

Late-onset manifestations of urea cycle disorders may be difficult to recognize and if left untreated can lead to devastating, life threatening consequences. We present the tragic case of a young man who presented with acute hyperammonemic encephalopathy due to ornithine transcarbamylase (OTC) deficiency unmasked by a high protein, ketogenic diet.

Case Description

A 30-year-old male with no significant medical history presented with altered mental status. He was an avid hiker with recent tick exposure. Two months previously, he started a ketogenic diet and was taking high dose protein shakes and anabolic mimetics to build muscle. Initial workup including computed tomography (CT) of the head, magnetic resonance imaging of the brain, electroencephalography, urine toxicology screen, cerebrospinal fluid culture for bacterial meningitis and tick borne illness was negative. He was found to have an ammonia level of 215 umol/L with no evidence of liver failure and undetectable alcohol level. He received one hemodialysis session but quickly deteriorated, developing seizures requiring intubation and mechanical ventilation. Repeat ammonia level worsened to 430 umol/L and repeat CT head showed diffuse cerebral edema with impending herniation. He was treated with hypertonic saline, mannitol, an extraventricular drain was placed, and he was initiated on continuous-renal replacement therapy. Despite improvement in ammonia level to < 20 umol/L, the patient failed to make a meaningful neurologic recovery. Genetic testing for an underlying urea cycle disorder revealed OTC deficiency.


Urea cycle defects result in the ability to breakdown protein and eliminate nitrogenous wastes, resulting in hyperammonemia. Symptoms vary from poor appetite, somnolence, and behavioral disturbances to rapid neurologic deterioration including seizures, coma, and death if not promptly recognized and treated. Although urea cycle disorders typically present shortly after birth, partial defects may manifest in adulthood in the context of increased catabolic stress. A high index of suspicion and rapid initiation of hemodialysis to remove ammonia is critical for a favorable outcome. We believe our patient’s high protein diet and use of anabolic mimetics precipitated a hyperammonemic crisis in the setting of mild OTC deficiency which unfortunately proved fatal.