IDH1 and oligodendroglioma: Specifically, adult-type diffuse gliomas are classified into two groups of IDH-mutant gliomas: (1) astrocytoma IDH-mutant (grade 2 to 4) and (2) oligodendroglioma IDH-mutant, 1p/19q-codeleted (grade 2 to 3), as well as glioblastoma IDH-wildtype (GBM, grade 4) [79].