National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Urea cycle disorders

A urea cycle disorder is a genetic disorder that results in a deficiency of one of the six enzymes in the urea cycle. These enzymes are responsible for removing ammonia from the blood stream. The urea cycle involves a series of biochemical steps in which nitrogen, a waste product of protein metabolism, is changed to a compound called urea and removed from the blood. Normally, the urea is removed from the body through the urine. In urea cycle disorders, nitrogen builds up in the blood in the form of ammonia, a highly toxic substance, resulting in hyperammonemia (elevated blood ammonia). Ammonia then reaches the brain through the blood, where it can cause irreversible brain damage, coma and/or death. The onset and severity of urea cycle disorders is highly variable. The severity correlates with the amount of urea cycle enzyme function.[1]
Last updated: 9/10/2013

The resources below provide information about treatment options for this condition. If you have questions about which treatment is right for you, talk to your healthcare professional.

Management Guidelines

  • The NORD Physician Guide for Urea cycle disorders was developed as a free service of the National Organization for Rare Disorders (NORD) and it's medical advisors.  The guides provide a resource for clinicians about specific rare disorders to facilitate diagnosis and treatment of their patients with this condition. 

FDA-Approved Treatments

The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition. Learn more orphan products.

  • Benzoate and phenylacetate (Brand name: Ammonul®) - Manufactured by Ucyclyd Pharma, Inc.
    FDA-approved indication: Adjunctive therapy in the treatment of acute hyperammonemia and associated encephalopathy in patients with deficiencies in enzymes of the urea cycle.
    National Library of Medicine Drug Information Portal
  • Sodium phenylbutyrate (Brand name: Buphenyl®) - Manufactured by Ucyclyd Pharma, Inc.
    FDA-approved indication: Adjunctive therapy in the chronic managment of patients with urea cycle disorders involving deficiencies of carbamylphosphate synthetase, ornithine transcarbamylase, or argininosuccinic acid synthetase.
    National Library of Medicine Drug Information Portal
  • Glycerol phenylbutyrate (Brand name: Ravicti) - Manufactured by Horizon Pharma, Inc.
    FDA-approved indication: Use as a nitrogen-binding adjunctive therapy for chronic management of adult and pediatric patients at least 2 months of age with urea cycle disorders (UCDs) that cannot be managed by dietary protein restriction and/or amino acid supplementation alone. RAVICTI must be used with dietary protein restriction and, in some cases, dietary supplements (eg, essential amino acids, arginine, citrulline, protein-free calorie supplements).
    National Library of Medicine Drug Information Portal
  • Benzoate and phenylacetate (Brand name: Ucephan ) - Manufactured by Immunex Immunex
    FDA-approved indication: For adjunctive therapy in the prevention and treatment of hyperammonemia in patients with urea cycle enzymopathy due to carbamylphosphate synthetase, ornithine, transcarbamylase, or argininosuccinate synthetase deficiency.
    National Library of Medicine Drug Information Portal

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • ClinicalTrials.gov lists trials that are related to Urea cycle disorders. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.

    Please note: Studies listed on the ClinicalTrials.gov website are listed for informational purposes only; being listed does not reflect an endorsement by GARD or the NIH. We strongly recommend that you talk with a trusted healthcare provider before choosing to participate in any clinical study.

Patient Registry

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

Living with a genetic or rare disease can impact the daily lives of patients and families. These resources can help families navigate various aspects of living with a rare disease.

Financial Resources

  • Good Days provides help to patients with life-altering conditions. Assistance includes help with the cost of medications and travel.
  • The HealthWell Foundation provides financial assistance for underinsured patients living with chronic and life-altering conditions. They offer help with drug copayments, deductibles, and health insurance premiums for patients with specific diseases. The disease fund status can change over time, so you may need to check back if funds are not currently available.

Education Resources

  • The Genetics Education Materials for School Success (GEMSS) aims to assure that all children with genetic health conditions succeed in school-life. Their Web site offers general and condition-specific education resources to help teachers and parents better understand the needs of students who have genetic conditions.

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Urea cycle disorders. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know.

  1. What is a Urea Cycle Disorder?. National Urea Cyle Disorders Foundation. http://www.nucdf.org/ucd.htm. Accessed 4/12/2017.