Based on the co-occurrence of IDH1 and IDH2 variants with variants in other genes in AML and glioma and on the fact that ~50% of the probands with OD and MS develop a malignancy including leukemia and glioma; we investigated the germline samples from probands with OD and MS for additional causative variants. The gene discussed is IDH1; the disease is osteochondritis dissecans.