PTPN11 and Noonan syndrome: SHP2, which is encoded by PTPN11, is a ubiquitously expressed PTPase that plays an essential role in the development and/or maintenance of multiple organs and tissues.34 Mutations in PTPN11 are associated with human Noonan syndrome,35,36 Leopard syndrome,37 and metachondromatosis (MC),38–41 all of which have severe skeletal manifestations.