What are urea cycle disorders?

Urea cycle disorders (UCDs) are a group of rare inherited genetic disorders

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The urea cycle is the process that turns harmful ammonia, which is created when the body digests protein, into urea so that the body can get rid of it through urine, as explained below:

The urea cycle is the only natural way to get rid of harmful ammonia. In people with UCDs, there is a problem with the enzymes that convert the ammonia to urea, and toxic ammonia can build up in the blood. Getting rid of excess ammonia is important because having too much ammonia in the body can lead to serious problems such as brain damage, coma, or even death. You or your loved one may or may not experience signs or symptoms of increased ammonia before these serious issues occur.

How common are urea
cycle disorders?

UCDs affect about 1 in 35,000 people in the United States. They can appear at birth or later in life, depending on the type and severity of the UCD.

Severe UCDs usually appear during the newborn (neonatal) phase of life. About 110 to 120 newborns are affected each year, but more than half don’t begin to show symptoms until after the newborn period.

In people with less severe UCDs, the first noticeable increase in ammonia can occur at almost any time of life, usually triggered by illness or stressful events such as viral infection, surgery, or prolonged fasting.

If you or a loved one has a UCD, speak with your or their doctor about a treatment plan.

Learn more about how UCDs affect children

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How common are urea cycle disorders?

UCDs affect about 1 in 35,000 people in the United States. They can appear at birth or later in life, depending on the type and severity of the UCD.

Severe UCDs usually appear during the newborn (neonatal) phase of life. About 110 to 120 newborns are affected each year, but more than half don’t begin to show symptoms until after the newborn period.

In people with less severe UCDs, the first noticeable increase in ammonia can occur at almost any time of life, usually triggered by illness or stressful events such as viral infection, surgery, or prolonged fasting.

If you or a loved one has a UCD, speak with your or their doctor about a treatment plan.

Learn more about how UCDs affect children

How are urea cycle disorders diagnosed?

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People with UCDs have a genetic abnormality that impacts their ability to get rid of nitrogen, leading to harmful levels of ammonia in the blood. This abnormality can be found with genetic testing, which is the preferred way to diagnose UCDs.

As frustrating as it may be, it is not unusual for a person with a UCD to get 1 or more incorrect diagnoses, as other conditions can have similar symptoms. Misdiagnosis can be problematic, because getting diet under control, working with a dietitian, and getting treatment as soon as possible is very important, as increases in ammonia levels over time can lead to damage within the body.>

If you or a loved one is experiencing symptoms or needs help managing a UCD, talk to a doctor as soon as possible.

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Sources

  1. Häberle J, Boddaert N, Burlina A, et al. Suggested guidelines for the diagnosis and management of urea cycle disorders. Orphanet J Rare Dis. 2012;7:32.
  2. Ah Mew N, Simpson KL, Gropman AL, Lanpher BC, Chapman KA, Summar ML. Urea cycle disorders overview [updated June 22, 2017]. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews® [Internet]. University of Washington; 1993-2022. Accessed March 20, 2022. https://www.ncbi.nlm.nih.gov/books/NBK1217/
  3. Weiner ID, Mitch WE, Sands JM. Urea and ammonia metabolism and the control of renal nitrogen excretion. Clin J Am Soc Nephrol. 2015;10(8):1444-1458.
  4. Häberle J, Burlina A, Chakrapani A, et al. Suggested guidelines for the diagnosis and management of urea cycle disorders: first revision. J Inherit Metab Dis. 2019;42(6):1192-1230.
  5. Summar ML, Dobbelaere D, Brusilow S, Lee B. Diagnosis, symptoms, frequency and mortality of 260 patients with urea cycle disorders from a 21-year, multicentre study of acute hyperammonaemic episodes. Acta Paediatr. 2008;97(10):1420-1425.
  6. Shchelochkov OA, Dickinson K, Scharschmidt BF, Lee B, Marino M, Le Mons C. Barriers to drug adherence in the treatment of urea cycle disorders: assessment of patient, caregiver and provider perspectives. Mol Genet Metab Rep. 2016;8:43-47.
  7. Batshaw ML, Tuchman M, Summar M, Seminara J, Members of the Urea Cycle Disorders Consortium. A longitudinal study of urea cycle disorders. Mol Genet Metab. 2014;113(1-2):127-130.
  8. Tuchman M, Lee B, Lichter-Konecki U, et al. Cross-sectional multicenter study of patients with urea cycle disorders in the United States. Mol Genet Metab. 2008;94(4):397-402.
  9. Algahtani H, Alameer S, Marzouk Y, Shirah B. Urea cycle disorder misdiagnosed as multiple sclerosis: a case report and review of the literature. Neuroradiol J. 2018;31(2):213-217.
  10. McGuire PJ, Lee HS, members of the Urea Cycle Disorders Consortium, Summar ML. Infectious precipitants of acute hyperammonemia are associated with indicators of increased morbidity in patients with urea cycle disorders. J Pediatr. 2013;163(6):1705-1710.