IDH1 and oligodendroglioma: This classification divided adult gliomas into three groups: (1) oligodendrogliomas, which harbor IDH mutations and 1p/19q codel, (2) astrocytomas, which are IDH mutant but without the 1p/19q codel, and (3) GBM, which are mostly IDH wild-type (WT) (Figure 2).