The high rate of multicentric gliomas, the identification of IDH mutations in all of the gliomas in which it could be fully assessed and the identical IDH mutations found in both the glioma and the skeletal tumor of two patients strongly suggest that, in most cases, similar to cartilaginous tumors, the development of gliomas in enchondromatosis patients results from somatic IDH mosaicism. Here, IDH1 is linked to Ollier disease.