Infants with complete enzyme deficiencies are usually born at term with no prenatal complications. Between 1 to 5 days of age they start feeding poorly, vomit frequently, become lethargic and hypotonic and may hyperventilate. Babies will progressively have tremor, stupor, seizures, apnea, coma, increased intracranial pressure and death if hyperammonemia is not diagnosed and treated effectively.

In patients with partial enzyme deficiencies, the first recognized clinical episode may be delayed for months or years; the hyperammonemia is less severe, and the symptoms are more subtle. In most late onset urea cycle disorders, the hyperammonemic episode is marked by loss of appetite, cyclical vomiting, lethargy, and behavioral abnormalities. Other possible symptoms include sleep disorders, delusions, hallucinations, and psychosis.

For more information on urea cycle disorder symptoms, please visit the Rare Diseases Clinical Research Network