Definition of Ornithine transcarbamylase (OTC) deficiency

Ornithine transcarbamylase (OTC) deficiency: A rare metabolic disorder, OTC is one of the urea-cycle disorders. The urea cycle is a series of five liver enzymes that help rid the body of ammonia, a toxic breakdown product of protein. When one of these enzymes is missing or deficient, ammonia accumulates in the blood and travels to the brain, causing coma, brain damage and death.

OTC deficiency is the most common of the urea-cycle disorders, occurring in one out of every 40,000 births. The genetic mutation responsible for OTC occurs on the X chromosome, so women are typically carriers, while their sons with the gene suffer the disease.

Severe OTC deficiency is a devastating disease. Typically, newborns slip into a coma within 72 hours of birth. Most suffer severe brain damage. Half die in the first month, and half of the survivors die by age 5.

Treatment includes a low-protein formula called keto-acid and sodium benzoate, a preservative, and another type of sodium, which binds to ammonia and helps eliminate it from the body.