SOS1 and Noonan syndrome: Mutations in the following genes that cause Noonan syndrome have been identified: RAS family GTPase proteins (KRAS, NRAS, RIT1, and RRAS), RAS signal function modulators (PTPN11, SOS1, SOS2, CBL, RASA2, and SHOCS2), and downstream signal transducers (RAF1 and BRAF) [3].