" Uera cycle disorder"
Disease
Urea cycle disorders, or UCDs, are a collection of inherited metabolic disorders in which affected patients suffer from high levels of systemic ammonia, a potent neurotoxin. Ammonia is produced via normal protein ingestion; the body normally detoxifies by converting it through a series of enzymatic steps to urea, which is excreted in urine.1
Infants born with a complete inability to synthesize urea may become catastrophically ill and comatose within a few days of birth and die if they are not promptly diagnosed and treated.2,3Children born with partial defects in urea synthesis may not be diagnosed until later in childhood or even adulthood, and may suffer from learning or occupational disabilities.4-6
Most UCD patients are at lifelong risk of hyperammonemic crises, sometimes several per year, in which ammonia levels rise in their blood and brain, and cause symptoms ranging from nausea, vomiting, and headache to coma and death.1These crises can be triggered by infections, postsurgery, or pregnancy.7
Regardless of severity, UCD patients and their families bear a heavy burden. Patients typically require a severely protein-restricted diet that may not resemble normal food, as well as dietary supplements. Even neurologically intact children may require special accommodation in school.7
Diagnosis and prevalence
UCDs occur in approximately 1 in 10,000 births worldwide.8The disease is diagnosed through either newborn screening or at presentation of symptoms. There are limitations to current newborn screenings, making it difficult to detect certain subtypes. Initial UCD symptoms range from catastrophic illness with coma occurring within a few days of birth to milder symptoms such as lethargy, headache, nausea, vomiting, disorientation, and seizures, particularly in patients who present later in life.1,2Because these symptoms are common to a number of ailments, physicians do not often consider the possibility of a UCD and, therefore, may not measure levels of blood ammonia. As a result, the most mildly affected patients can go undiagnosed for a period of time despite having symptoms.1Because many cases of UCDs remain undiagnosed and because infants born with severe UCDs often die without a definitive diagnosis, the exact incidence and prevalence of UCDs are unknown.2
Current treatment options
Management of UCDs involves decreasing ammonia production through reduction of protein in the diet, amino acid supplementation, and the use of ammonia-lowering agents.9Many patients with mild to moderate disease manage their conditions through protein restriction alone and risk long-term complications if the underlying disease is not well controlled.