Recently, germline mutations of PTPN11 have also been identified in approximately 50% of cases of another bone disease, metachondromatosis (OMIM 156250), which is characterized by the development of benign exostotic and endosteal cartilagenous tumors (Kennedy, 1983; Bowen et al., 2011). Here, PTPN11 is linked to metachondromatosis.