IDH1 and astrocytoma (excluding glioblastoma): This study indicates that ALT may be the major telomere maintenance mechanism in IDH1 mutation astrocytoma resulting in histidine substitution at arginine 132 (IDH1R132H) mutated astrocytomas and that IDH1R132H downregulates ATRX expression in vitro resulting in ALT (Ferreira et al. 2020).