Urea cycle disorders (UCDs) are a group of hereditary conditions in which the body struggles to remove waste produced during the digestion of proteins. As they are inherited conditions, they are commonly seen in children and infants and may be life-threatening if left untreated.

In a normal urea cycle, the liver makes enzymes to turn waste nitrogen into urea, which is expelled from the body as urine. Patients with UCDs are deficient in or fail to produce, certain enzymes required for a normal urea cycle. There are eight varieties of urea cycle disorder, defined by the enzyme or other substance missing from the cycle. The severity of UCDs varies depending on the part of the cycle affected.

Symptoms of severe UCDs may include fatigue, vomiting, seizures, respiratory arrest, confusion, and coma.

Treatment of UCDs may involve dialysis to remove ammonia from the blood, taking supplements containing sugars, fats and amino acids, and medication. Long-term treatment may also involve following a diet low in protein and high in calories, drinking plenty of water, and medication in the form of urea cycle disorder agents.