IDH1 and oligodendroglioma: Adult-type diffuse gliomas are further subclassified into astrocytoma (IDH mutant, CNS WHO Grades 2–4), oligodendroglioma (IDH mutant and 1p/19q-codeleted, WHO Grades 2 and 3), and glioblastoma (IDH wildtype) (Louis et al., 2021).