Germline pathogenic variants result in similar yet distinct syndromes, which include Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NSMLs), Costello syndrome (CS), cardiofaciocutaneus syndrome (CFCS), neurofibromatosis type 1 (NF1), and other clinically related diseases, for example, Legius syndrome, Mazzanti syndrome (NS with loose anagen hair [NSLAH]), and CBL‐related and MAPK1‐related disorders. The gene discussed is MAPK1; the disease is Netherton syndrome.