Subsequent studies showed that recurrent missense mutations involve IDH1 at position arginine 132, and less commonly in the homologous arginine 172 of IDH2. Overall, IDH1 R132 and IDH2 R172 alterations occur in about 80–90% of adult WHO grade II or III infiltrating astrocytomas, oligodendrogliomas, and secondary glioblastoma [42]. Here, IDH1 is linked to oligodendroglioma.