Ornithine transcarbamylase (OTC) deficiency is a rare, genetically transmitted error of protein metabolism. OTC is one of several enzymes essential to the urea cycle, a series of related chemical reactions by which ammonia, a by-product of protein breakdown, is converted to urea and rapidly removed by the kidney. An absence or inadequacy of OTC causes accumulations of ammonia in tissue and blood (hyperammonemia). This hyperammonemic state is extremely toxic to nerve cells and is responsible for the symptoms and lingering sequelae of this disorder.
The most common urea cycle enzyme deficiency disorder inherited as an autosomal recessive trait, characterized by the absence of ornithine transcarbamylase (an enzyme in the urea cycle), which results in the excessive buildup of ammonia in the bloodstream. The disease is typically diagnosed in infancy and occurs in less than 1 in 8000 births.