The severity of the disorder, the inability to develop and test therapies in a representative model not requiring postnatal somatic gene modification and the necessary 3- to 4-week gene ramp down before Cps1 protein depletion reaches critical levels (Khoja et al., 2018) led us to develop a new mouse model with longevity and mild to moderate hyperammonemia. Here, CPS1 is linked to Hyperammonemia.