A urea cycle disorder (UCD) is an inherited disease. When we eat protein our bodies break it down into amino acids which we need to grow and stay healthy. Extra amino acids that our body doesn’t need are turned into a waste product called ammonia. Enzymes in the liver turn the ammonia into urea so the body can get rid of it through the urine. 

In someone with a UCD, the enzyme is missing or is not working correctly. Because of this, ammonia builds up in the blood and it can be harmful. It can travel to the brain and cause memory loss, behavior changes, coma, seizures, or brain damage. UCDs affect 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. 

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UCD symptoms can be subtle and similar to many other conditions, which can lead to misdiagnosis. These symptoms can include headaches, fatigue (feeling tired), confusion, and trouble concentrating. Any level of elevated ammonia, even if it’s not high enough to cause severe symptoms or a hyperammonemic crisis, should be avoided in order to prevent brain damage.

Learn about the long-term effects of a UCD on the body and brain

Healthy urea cycle diagram with normal serum ammonia levels and urea production
Urea Cycle Disorder diagram showing how break in cycle causes high ammonia levels

Healthy Urea Cycle

Protein in the food you eat is needed for the growth and development of your body.

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 into urea as well as it should. 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.

While UCDs start in your liver, it’s important to remember that elevated ammonia levels have the biggest effect on your brain.

UCD genes icon

A UCD is a genetic disorder. This means it is caused by a defective gene, which can be inherited from one or both parents. UCDs can also be caused by a random genetic mutation. There are different types of urea cycle disorders. The most common type of UCD is ornithine transcarbamylase deficiency (OTC). It is typically passed from a mother to her child. A mother who is an “OTC carrier” may not know she carries the OTC gene until her child is diagnosed. However, mothers who are “OTC carriers” can have mild UCD symptoms that should not be ignored.

Map of Ornithine Transcarbamylase Deficiency, Citrullinemia, Arginase Deficiency and other UCD subtypes

Fortunately, there are options for people with urea cycle disorders to help control high levels of ammonia in the body. Options can include a low-protein diet, amino acid supplements, and ammonia-controlling medicines. Because every person’s needs are different, it’s important to talk to your doctor to develop a plan for how you can best manage your ammonia levels. 

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