Furthermore, the new 2021 WHO classification divides adult-type diffuse gliomas into three different groups based on the mutations and copy number alterations they harbor: (1) astrocytoma, isocitrate dehydrogenase (IDH)-mutant, (2) oligodendroglioma, IDH-mutant and 1p/19q codeleted, and (3) glioblastoma, IDH-wildtype4. The gene discussed is IDH1; the disease is oligodendroglioma.