Urea cycle disorders


What are urea cycle disorders?

A urea cycle disorder (UCD) is a group of genetic diseases that are caused by malfunctions in one or more parts of the urea cycle. The urea cycle is the body’s way of neutralizing highly toxic ammonia, produced from protein breakdown, into the less toxic urea, which can be removed by the urine. Individuals with UCD are deficient in or missing key parts of the urea cycle, including transporters, which move essential materials to the cycle, or enzymes, which complete sequential steps in the cycle to remove waste from the body. Defects in one or more of these enzymes or transporters leads to high levels of ammonia in the blood (hyperammonemia), which can cause serious complications, including permanent neurological damage, coma, or death.

Common urea cycle disorders

Transporter malfunctions:

  • Citrin
  • Ornithin Translocase

Enzyme deficiencies:

  • N-Acetylglutamate Synthetase (NAGS)
  • Carbamoyl Phosphate Synthetase (CPS-1)
  • Argininosuccinate Synthetase (ASS)
  • Argininosuccinate Lyase (ASL)
  • Arginase (ARG1)
  • Ornithine Transcarbamylase (OTC)

How common are urea cycle disorders?

The number of individuals with a urea cycle disorder is estimated to be 1 in every 30,000 births in the US. Infants born with severe UCD deficiencies may present with complications within hours to days after birth. However, individuals with only partial enzyme or transporter deficiency may not be diagnosed until much later - usually when surgery, infection, or other medical complications further impair their ability to break down protein or the if patient’s dietary intake of protein increases. The rarity of these disorders and high early mortalilty of UCDs make diagnosis difficult, and early diagnosis and treatment are crucial to improving survival and preventing brain damage. Disease onset in the first 30 days of life carries a 50% mortality rate. Recent advances in treatment have reduced the mortality in children and adults.

In patients with suspected urea cycle disorders, family history, blood chemistries, enzyme activity from liver biopsy and genetic testing can identify which components of the urea cycle are defective. In individuals with family history of known or suspected urea cycle disorders, genetic counseling and pregnancy planning is strongly recommended.

Questions regarding your urea cycle disorder?

You can reach the urea cycle disorder care team, anytime, day or night, seven days a week.

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What are the symptoms of urea cycle disorder?

Symptoms related to high levels of ammonia in the blood (hyperammonemia) include, but are not limited to:

Newborn Children – initial symptoms

  • Failure to feed
  • Inability to maintain normal body temperature (low core body temperature)
  • Abnormal drowsiness
  • Loss of appetite
  • Breathing too fast or too slow
  • Seizures
  • Abnormal body posturing (indicator of brain toxicity)

Any Age (Mild or partial UCD)

  • Loss of appetite
  • Vomiting
  • Abnormal behaviors
  • Abnormal behaviors associated with sleep:
    • Difficulty falling or staying asleep
    • Falling asleep at inappropriate times
    • Excessive total sleep time or drowsiness
    • Delusions
    • Hallucinations


Urea Cycle Disorder

The following specialty medications are available at Accredo, a specialty pharmacy for urea cycle disorder.

Medication Manufacturer
Carbaglu® (carglumic acid) Recordati Rare Diseases Inc
Pheburane® (sodium phenylbutyrate) Medunik
Ravicti® (glycerol phenylbutyrate) Horizon Pharma, Inc

Financing Your Care

Financial assistance is available to support your drug costs including manufacturer and community programs. Accredo specialists are available to assist in finding the right program for you.

Financial Guidance

Life-saving specialty medication can be expensive. Learn how the Accredo teams help individuals find ways to afford the medication they need to survive in this video.

Find Support

Urea Cycle Disorder Organizations

There are many organizations that support research and advocacy for Urea Cycle Disorder. See below for a few of those organizations.

Support Organizations

Government Organizations

Meet the Team

Accredo’s Urea Cycle Disorder care team is dedicated to serving you and understands the difficulty of this complex condition. Our expert clinicians are always available, 24 hours a day, seven days a week, to answer any questions.

Why We Do It

Accredo supports patients with chronic and complex conditions and helps them live their best life. Watch our video to learn why we do what we do for our patients.

Why We Do It video transcript

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