CPS1 and Hyperammonemia: CPS1 catalyzes the initial and limiting step of the urea cycle, which is critical in the detoxification of excess ammonia, so CPS1D patient suffering from hyperammonemia will present a decreased level of citrulline but elevated glutamine in blood amino acid analysis, and a low level of orotic acid in urine test (Funghini et al., 2012; de Cima et al., 2015; Ali et al., 2016).