NS, NS with multiple lentigines (NSML), and NS-like syndromes are associated with variants in multiple genes including PTPN11, KRAS, NRAS, and RAF1. Costello syndrome is associated with variants in HRAS, while cardiofaciocutaneous syndrome is associated with variants in BRAF, MEK1, MEK2, and KRAS. These differences are associated with important differences in disease presentation (Rauen, 2013). Here, KRAS is linked to Costello syndrome.