Mutations in the isocitrate dehydrogenase (IDH)1 and2 genes are present in 85% of hereditary enchondromatosis-associated disorders, Ollier disease (enchondromatosis only), and Maffuci syndrome (enchondromatosis and hemangiomas) and 50% of solitary enchondromas21. The gene discussed is IDH1; the disease is Ollier disease.