CPS1 and hyperinsulinemic hypoglycemia, familial, 4: Carbamoyl phosphate synthetase I (CPS1) deficiency (CPS1D) is a rare autosomal recessive urea cycle disorder, characterized by hyperammonemia with the incidence of 1/50,000 to 1/300,000 (Díez-Fernández et al., 2015).