Primary urea cycle disorders (UCDs) include carbamoyl phosphate synthase (CPS) deficiency, ornithine transcarbamylase (OTC) deficiency, argininosuccinate synthetase deficiency (citrullinemia), argininosuccinate lyase deficiency (argininosuccinic aciduria), arginase deficiency (argininemia), and N - acetylglutamate synthetase (NAGS) deficiency.