The urea cycle is a process in which waste (ammonia) is removed from the body. When you eat proteins, the body breaks them down into amino acids. Ammonia is produced from leftover amino acids, and it must be removed from the body.
The liver produces several chemicals (enzymes) that change ammonia into a form called urea, which the body can remove in the urine. If this process is disturbed, ammonia levels begin to rise.
Several inherited conditions can cause problems with this waste-removal process. People with a urea cycle disorder are missing a gene that makes the enzymes needed to break down ammonia in the body.
Urea cycle disorders occur in about one in 30,000 newborns.
Source: National Library of Medicine (NLM)