Skip to main content

Recognize the signs

What are the Symptoms

What are the Symptoms?

Newborns with severe urea cycle disorders become catastrophically ill with symptoms that mimic sepsis—failure to feed, lethargy, respiratory distress, seizures and ultimately coma.

Children and adults with milder (or partial) urea cycle enzyme deficiencies may go years without a diagnosis, until a trigger—a high protein meal, viral illness, excessive exercise or calorie deficiency—causes excessive ammonia to be produced in the body, resulting in critical elevations of blood ammonia levels. 

The symptoms may be subtle and go unrecognized for years until a trigger results in catastrophic hyperammonemia. Children and adults with undiagnosed urea cycle disorders may experience only occasional subtle symptoms—nausea, gastric distress, irritability, fatigue, lethargy—or a spectrum of issues from mild to severe developmental delay, learning disabilities, hyperactivity, autism, seizures, behavioral abnormalities, psychiatric disturbances, mood changes, migraine-type headaches, cyclic vomiting.


Because newborns are usually discharged from the hospital within one to two days after birth, the symptoms of a urea cycle disorder may be subtle until the child is at home and may not be recognized in a timely manner by the family or medical professionals. Very early symptoms in an infant with hyperammonemia can be non-specific. Sepsis is often suspected. It is recommended that serum ammonia level be included in standard sepsis workup in order to quickly detect hyperammonemia in these infants.

  • Refusal to Feed
  • Vomiting
  • Irritability progressing to lethargy and somnolence
  • Hypothermia
  • Seizures
  • Hyperventilation leading to respiratory alkalosis
  • Neurologic posturing
  • Hypoventilation with respiratory arrest
  • Coma

Children and Adults

In children and adults with mild to moderate (partial) urea cycle enzyme deficiencies, the first recognized episode may be delayed for months or years. Although the symptoms vary, a hyperammonemic episode may be marked by a spectrum of symptoms:

  • Loss of Appetite
  • Vomiting
  • Lethargy
  • Behavioral Abnormalities
  • Agitation
  • Sleep Disorder
  • Confusion
  • Delusions
  • Hallucinations
  • Psychosis
  • Bizarre/Unusual Behavior
  • Stroke-like Symptoms