CPS1 and hyperammonemia due to N-acetylglutamate synthase deficiency: Differential diagnosis between NAGSD and other UCDs is important, as a specific and effective treatment for NAGSD using N-carbamylglutamate, a structural analogue of the natural CPS1 activator (NCG; carglumic acid; Carbaglu, Orphan Europe, Paris France), is available [9].