Molecular biology studies are the cornerstones of the new 2021 WHO classification of tumors of the CNS and allow the classification of high-grade gliomas and some frequently associated mutations: glioblastoma (GBwt-IDH), in which mutations in the TERT promoter, EGFR promoter, chromosome 7 trisomy, and monosomy chromosome 10 are frequent; astrocytoma (Amut-IDH,G3-4), in which mutations in the ATRX, TP53 and CDKN2A/B genes can be found; and oligodendroglioma (Omut-IDH,codel-1p/19q,G3), in which TERT, CIC, FUBP1, and NOTCH1 promoter mutations are common (8, 18). The gene discussed is ATRX; the disease is astrocytoma (excluding glioblastoma).