The most credited pathogenetic model of LPI to date identifies key injurious stimuli in an abnormal intracellular entrapping of arginine due to the absence of a functional 4F2hc/y+LAT1 complex and, in turn, in an unbalanced metabolism of the amino acid through pathways that differ among cell types (3); in particular, an overproduction of nitric oxide by nitric oxide synthase 2 (NOS2) in macrophages is supposed to be central to the development of immune dysfunctions (31). Here, NOS2 is linked to lysinuric protein intolerance.