Diagnosis of NS is established genetically by finding pathogenic variant in any of the following genes: PTPN11, SOS1, SOS2, RAF1, KRAS, NRAS, MRAS, MAP2K1, BRAF, RASA2, LZTR1, RRAS and RIT1. Noonan syndrome with multiple lentigines (NSML or LEOPARD syndrome), must also be included in the differential diagnosis. Here, MAP2K1 is linked to Noonan syndrome.