A Case of Atypical Adult Presentation of Urea Cycle Disorder

Urea cycle disorders are metabolic disorders of nitrogenous waste substances due to either complete or partial deficiency of enzymes. Hyperammonemia associated with urea cycle disorders should be addressed immediately in the acute setting, as it can cause irreversible neurological injury or death.

We report the case of a 48-year-old woman who presented with lethargy, weakness, and altered mental status following prolonged nausea and vomiting despite an esophageal dilatation procedure 3 weeks prior. Further investigation with assistance from the genetics consult team revealed a partial enzyme deficiency associated with urea cycle disorder.

Although many cases of urea cycle disorder present in neonates 24 to 48 hours following birth, a delayed presentation may be observed in female carriers with partial activity of any urea cycle enzyme leading to ammonia buildup. This is the result of stress-related events that form a catabolic state involving protein breakdown within the body that trigger increased ammonia levels.

A diagnosis of urea cycle disorder should be suspected in patients who have had a recent stressor with progressive lethargy and confusion associated with hyperammonemia, so that treatment may begin with intravenous sodium benzoate and phenylacetate initially and hemodialysis at 8 hours if ammonia levels do not decrease to avoid permanent neurologic damage.