IDH1 and oligodendroglioma: The 2021 WHO glioma classification emphasizes the molecular markers isocitrate dehydrogenase (IDH), alpha-thalassemia mental retardation X-linked (ATRX), and codeletions of both the short arm of chromosome 1 (1p) and long arm of chromosome 19 (19q), or 1p19q codeletion, alongside traditional histology, to establish integrated diagnoses of astrocytoma, oligodendroglioma, or glioblastoma.1