IDH1 and astrocytoma (excluding glioblastoma): In contrast to oligodendrogliomas and IDH-wildtype glioblastoma, TERT promoter mutations are rare in IDH-mutant astrocytomas, which instead maintain telomere length through a mechanism involving mutations in the ATRX gene, usually accompanied by mutations in TP53. ATRX encodes α-thalassemia/mental retardation syndrome X-linked, a protein that, along with death-domain associated protein or DAXX, is involved in maintaining chromatin structure at the telomeres [54].