The utility of H3K27me3 immunostaining in the differential diagnosis between oligodendroglioma and astrocytoma was first reported by Filipski et al. [14], who suggested that H3K27me3 retention indicates astrocytic (non-codeleted) tumours with a predicted probability of 0.9995, while its loss in IDH-mutant gliomas with retained or non-conclusive ATRX stain is 100% specific for oligodendrogliomas [14]. The gene discussed is ATRX; the disease is oligodendroglioma.