IDH1 and oligodendroglioma: Adult-type diffuse gliomas are divided into three subtypes: (1) IDH—mutant astrocytoma (Grade 2, 3, 4); (2) IDH—mutant and 1p19q co-deleted oligodendroglioma (Grade 2, 3); and (3) IDH—wildtype glioblastoma (Grade 4).