A genetic disorder involving a deficiency of one of the enzymes needed in the urea cycle. The urea cycle is the process of removing ammonia from blood stream by converting it to urea and excreting it via urine. A build-up of ammonia in the blood is toxic to the body and can cause serious brain damage. The progressively severe symptoms usually become obvious within the first few weeks of birth. Nevertheless, mild or partial enzyme deficiencies may cause little or no symptoms or symptoms that don't start until later in life. See also Inborn urea cycle disorder