The TERT promoter is frequently altered in glioblastomas through mutations mapping to positions 124 and 146 bp upstream of the TERT ATG start site; interestingly, glioblastomas with non-mutated TERT promoters harbor ATRX mutations, usually concurrently with IDH1 and TP53 mutations: this observation is in line with the role of ATRX in alternative lengthening of telomeres and strongly supports the conclusion that maintenance of the telomere is an obligatory step in glioblastoma pathogenesis. The gene discussed is ATRX; the disease is glioblastoma.