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Urea Cycle Disorder Facts

A urea cycle disorder (UCD) is a rare disease that affects about 1 in 35,000 births in the United States. Just because it’s rare doesn’t mean there isn’t information to help you or someone you love who is living with a UCD. Here are some facts to help you better understand a UCD.

Consultar más información sobre los UCD en español.

It's in the Genes

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A UCD is a genetic disorder that is passed on to a child. See below to learn how it happens and what genetic testing can show.

graphic of a baby for UCD genetic explanation

A urea cycle disorder (UCD) is something a person is born with.

graphic explaining UCD is a genetic disorder

Everybody has 2 copies of each gene,
1 from the mother and 1 from the father.

graphic explaining the defective parent genes of a UCD

Urea cycle disorders can be passed down when each parent gives a UCD gene to the child. One UCD subtype, ornithine transcarbamylase (OTC) deficiency, can also be inherited in an X-linked. way, where the gene is passed on from the mother. UCDs can also be caused by a spontaneous genetic mutation.

logo graphic that represents OTC deficiency

OTC deficiency is the most common urea cycle disorder subtype. It is passed on from a mother to her child via the X chromosome. In rare cases, OTC can also be passed down from a father to his daughter. Mothers with OTC are often called carriers. This is because they may not know they carry the OTC gene until their child is diagnosed. However, carriers can have subtle UCD symptoms, like headaches, fatigue, and nausea or vomiting. Any carrier who experiences symptoms should talk to a doctor about UCD management.

spyglass graphic explaining the abnormal UCD gene

A carrier is a person who has 1 normal copy of a gene and 1 abnormal copy.

UCD genetic testing test tube graphic

Genetic testing can discover if a person is or isn't a carrier and determine the chances of passing on a UCD gene.

Learn whether you may be an OTC carrier

The Urea Cycle and UCDs

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diagram of a liver showing a healthy urea cycle diagram explaining urea cycle disorder in the liver

Healthy Urea Cycle

Protein found in food enters the body to be absorbed by cells for growth and development.

Our bodies break down the protein we eat into amino acids, which the body needs to grow and stay healthy. The extra protein that our bodies do not need contains nitrogen, which is turned into ammonia.

The ammonia is then removed from the blood, turned into urea, and passed from the body through urine.


Urea Cycle Disorder

When a person has a urea cycle disorder, the urea cycle can't change the ammonia effectively into urea. The ammonia builds up because the body can't get rid of it.

The ammonia can reach toxic levels in the blood and can trigger vomiting, confusion, and swelling in the brain.

Spot the Symptoms of a UCD

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Normal things in life, like being sick, stressed out, and eating too much food high in protein, can cause ammonia to rise to toxic levels. This can trigger a hyperammonemic crisis, which requires immediate medical attention. Take a look at these common symptoms of high ammonia levels that could signal a crisis.

UCD symptom tired icon

Feeling very tired
or sluggish

UCD symptom zoning out icon

Staring or

UCD symptom nausea icon

or vomiting

UCD symptom hallucinating icon

Losing touch with

UCD symptom irritable icon

Unusually irritable or uncooperative

UCD symptom aggression icon


UCD symptom lack of appetite icon

Lack of appetite

UCD symptom slurring words icon

Slurring words

UCD symptom headaches icon


Managing Your Urea Cycle Disorder

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There are options to help control high levels of ammonia for people with urea cycle disorders (UCDs). Because every person's needs are different, it's important to talk to your doctor to develop a plan on how you can best manage your ammonia levels.

Low-protein diet

It's important to limit protein when living with a UCD. But limiting it too much may harm your body at the same time because we need protein to grow. Common triggers, like being stressed or getting sick, can increase ammonia to toxic levels despite your best efforts to balance how much protein you eat.

Amino acid supplements

Amino acids are essential nutrients that are needed to grow and maintain your health. The body creates amino acids when it breaks down protein. If you are on a low-protein diet, amino acid supplements can fill the gap for the nutrients your body cannot make itself. A dietitian who is part of your healthcare team can help decide which supplements may be right for you.  

Nitrogen scavengers (also called "ammonia scavengers")

When the urea cycle can't get rid of ammonia, a treatment that gets rid of the excess ammonia may be needed. Nitrogen scavengers, sometimes called "ammonia scavengers," help remove ammonia from the bloodstream.

Liver transplant

Living with a urea cycle disorder means that certain enzymes in your liver aren't working properly. A liver transplant can cure a UCD so the enzymes work the way they should. The transplant can't fix any health problems that happened beforehand and the procedure has risks.

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Use the information on this page to talk to your doctor about UCDs and how to help manage elevated ammonia levels with a treatment plan that works for you.

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