Noonan syndrome is caused by activating mutations in a number of RAS pathway genes (most commonly PTPN11, SOS1, RAF1), and together with other similar, so-called RASopathy syndromes, over 20 genes have been implicated in this group of disorders which include Noonan syndrome with multiple lentigines, Cardiofacio cutaneous syndrome (associated with BRAF, MAP2K1, and MAP2K2), Costello syndrome (associated with HRAS), among others (98). The gene discussed is PTPN11; the disease is Noonan syndrome.