Urea Cycle Disorders

Urea cycle disorders (UCDs) are rare genetic conditions that affect how the body gets rid of extra nitrogen. Most of the nitrogen in our bodies comes from the proteins we eat as part of our normal diet. Extra nitrogen we do not use is changed into urea. This process is called the urea cycle. The body gets rid of urea through urine (pee).

When the body cannot remove extra nitrogen, ammonia builds up in the blood. Too much ammonia in the blood can be dangerous because it can enter the brain and cause neurological symptoms. 

UCDs are rare diseases that affect fewer than 1 in 10,000 people. Both males and females can have UCDs. Symptoms may appear soon after birth or later in life, depending on which enzyme in the urea cycle is affected.

Urea cycle disorder symptoms

Urea cycle disorders can cause the following symptoms: 

• Weakness or fatigue
• Balance issues
• Vomiting
• Loss of appetite 
• Confusion or trouble thinking clearly
• Seizures
• Stroke
• In babies, poor feeding and unusual sleepiness 
• Coma

Urea cycle disorder causes

UCDs are caused by changes (mutations) in certain genes. These mutations may be passed down from parents to their children (inherited). In some cases, a patient may be the first in their family to have these gene changes (de novo). 

Specific genes give the body instructions to make enzymes. Some enzymes are special proteins that help the body remove nitrogen from food safely. People with UCDs have gene mutations that affect these enzymes so they do not work right. 

When the enzymes do not work right, the urea cycle does not work as it should. This makes ammonia build up in the blood and brain, which is dangerous. 

Urea cycle disorder care at St. Jude

St. Jude Children’s Research Hospital is working to better understand rare, catastrophic genetic neurological disorders in children, including UCDs. Our goal is to change how these disorders are treated. The Center for Experimental Neurotherapeutics (CENT) was started at St. Jude as part of the Pediatric Translational Neuroscience Initiative (PTNI) to focus on these neurological disorders.

Children with UCDs who are accepted at St. Jude may take part in clinical research or clinical trials, as they become available. These studies help scientists learn more about UCDs. They may also help scientists develop new treatments.  

Urea cycle disorder clinical trials

Learn more