NS is caused by germline mutations in genes coding for transducers and modulatory proteins with a role in the RAS–MAPK signaling cascade (i.e., PTPN11, SOS1, SOS2, KRAS, NRAS, RIT1, LZTR1, RAF1, and MEK1) [5,6], and, together with the clinically related NS with multiple lentiginous (NMLS, formerly called LEOPARD syndrome, OMIM PS151100), cardiofaciocutaneous syndrome, Costello syndrome and Noonan syndrome-like disorder with loose anagen hair, constitutes a group of known as RASopathies. This evidence concerns the gene MAP2K1 and Netherton syndrome.