Urea Cycle Disorders

Ashley, a child with ucd

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For healthcare providers: Additional clinical information

Urea cycle disorders are a group of genetic conditions that fall under the broad category of metabolic disorders. The urea cycle is a biochemical process that occurs in the liver. Through this process, body waste from the metabolism of protein (in the form of nitrogen) is removed from the blood and converted to a compound called urea. There are eight enzymes that complete this process, and normally the urea is transferred into the urine and removed from the body. 

However, in urea cycle disorders, one of the enzymes in the cycle is deficient. Without the proper enzymes, the process can't be completed, and nitrogen accumulates in the blood in the form of ammonia, a highly toxic substance. The accumulation of ammonia in the blood is called hyperammonemia. Hyperammonemia is especially toxic to the brain and can cause brain damage, coma or death. 

UCDs are caused by a genetic mutation. Some children are diagnosed as children because they show symptoms. Other children are diagnosed as infants through new-born screening (NBS). Children diagnosed by NBS may receive treatment before they first experience symptoms. 

Learn more about the physical characteristics and/or symptoms of different types of UCDs.


This information was last updated in December, 2015.