IDH2 and osteosarcoma: Three types of mutations caused three types of mutant IDH1 (R132C, R132G, and R132H) genes while four types of mutations causing three types of mutant IDH2 (R172S, R172T, and R172W) genes in cartilaginous tumors (S1 Fig); however, no mutations were detected in osteochondromas or osteosarcomas (Tables 1 and Table 2).