ATRX and glioblastoma: Furthermore, we identify a novel mechanism of telomerase activation in glioblastomas that occurs via chromosomal rearrangements upstream of TERT. Collectively, our findings define novel molecular subgroups of glioblastoma, including a telomerase-positive subgroup driven by TERT-structural rearrangements (IDHWT-TERTSV), and an ALT-positive subgroup (IDHWT-ALT) with mutations in ATRX or SMARCAL1.