Although it remains unclear how ALT becomes activated, its presence has been tightly associated with loss-of-function events targeting the α-thalassemia/mental retardation syndrome X-linked (ATRX) or death-domain-associated protein (DAXX) genes and these events are also a hallmark feature of IDH-mutant astrocytomas [84, 98, 104]. This evidence concerns the gene IDH1 and astrocytoma (excluding glioblastoma).