Urea cycle disorders (UCD) are rare inherited metabolic disorders with an incidence estimated to be 1: 35,000 births. UCDs are caused by the dysfunction of any of the six enzymes (namely, carbamoyl phosphate synthetase I, N-acetylglutamate synthetase, ornithine transcarbamylase, argininosuccinic acid synthetase, argininosuccinate lyase, and arginase) or the two transport proteins (ornithine translocase and aspartate/glutamate carrier) involved in urea biosynthesis. The urea cycle converts the highly toxic ammonia produced from amino acid catabolism into urea, for excretion via the kidneys. A defect in urea synthesis results in hyperammonemia.