Urea Cycle Disorders


Newborn Children

Initial symptoms of hyperammonemia (too much ammonia in the blood) in the newborn are non-specific:

  • Failure to feed,
  • Inability to maintain normal body temperature with a low core body temperature,
  • Drowsiness
  • Symptoms progress from sleepiness to abnormal drowsiness and coma [Brusilow 1985, Batshaw & Berry 1991, Summar 2001].

Symptoms may progress in the newborn that appears normal but rapidly develops cerebral edema (swelling of the brain). Symptoms of cerebral edema include the following:

  • Lethargy-abnormal drowsiness
  • Anorexia- loss of appetite
  • Breathing too fast or too slow
  • Hypothermia- low body temperature
  • Seizures
  • Neurologic posturing (abnormal body position due to brain toxicity)

Any Age

Milder (or partial) urea cycle enzyme deficiencies can be triggered by illness or stress at almost any time of life resulting in multiple mild elevations ammonia in the blood. The first recognized clinical episode may be delayed for months or years. [Bourrier et al 1988] Hyperammonemic episode (too much ammonia in the blood) is marked by the following:

  • Loss of appetite,
  • Repeated vomiting,
  • Lethargy, abnormal drowsiness,
  • Abnormal behavior,
  • Sleep disorder  difficulty falling or staying asleep, falling asleep at inappropriate times, excessive total sleep time, or abnormal behaviors associated with sleep ,
  • Delusions a false belief in things that are not true despite the facts,
  • Hallucinations perception of something (as a visual image or a sound) with no known external cause,
  • Psychosis loses touch with reality
  • Changes may be seen on an Electroencephalogram (EEG) and Magnetic Resonance Imaging (MRI) [Batshaw 1984, Brusilow 1985, Bourrier et al 1988].
Tests to diagnose: 

The diagnosis is made by analysis of the urine for abnormal metabolites (substance produced by metabolism). Tests will be done to check the blood for high ammonia levels and to check amino acid levels in the child.

A liver biopsy can be done to confirm the diagnosis since it can show low levels of enzyme activity. Genetic tests also can be done to show whether there is a problem with one of the genes needed to break down proteins of the urea cycle, and they can identify the particular type of urea cycle disorder.

A Magnetic Resonance Imaging (MRI) or Computerized Tomography (CT) scan may be done to see if there is swelling of the brain caused by the ammonia in the blood.


Treatment is a lifelong process that doesn't cure the condition, but it can effectively manage the symptoms. Frequent blood tests are done to continue to monitor ammonia levels. Doctors in the areas of pediatrics, genetics and nutrition will work together to develop the child's treatment plan.

The child's treatment probably will involve:

  • Low protein, high-calorie diet. Protein in the diet is lowered by avoiding protein-rich foods. Examples of foods that provide calories without loading the body with protein are fruits, vegetables and starches.
  • However, protein is important for growth, so the protein restriction must be done with advice from a healthcare professional. A dietitian will plan and update a protein-restricted diet as the child grows.
  • Medications. Some children will need to take medicine to help take extra ammonia out of the body. Oral medication is given that binds to ammonia and carries it out in the urine.
  • Amino acid supplements. Depending on the type of UCD, amino acid supplements such as arginine or citrulline may be added to the diet to help give the body what it needs to make proteins that are important for growth and tissue repair, since children with urea cycle disorder can't make arginine on their own.
  • Liver transplantation. Because the production of urea cycle enzymes takes place in the liver, a liver transplant can be an effective treatment for urea cycle disorder.

If a transplant is the best treatment option, the doctor and the other members of the patient care team will focus on preventing complications and will treat symptoms while your child waits for the donated liver.

Stresses on the body, such as illness, fever, surgery or an accident, can cause ammonia levels to rise. Care must be taken at these times, and extra calories will be needed to provide the stressed body with fuel.

Visits with your doctors and other specialists will be necessary to make adjustments to diet and medication. Having your child follow the diet your doctor gives is important for the child's health, growth and development.

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