IDH1 and glioblastoma: This alteration, usually at arginine 132 (IDH1-R132H), is highly frequent in diffuse low-grade gliomas (LGGs; WHO grade II), in anaplastic astrocytomas (WHO grade III), and also in a smaller proportion of HGG originated from LGGs (secondary glioblastomas; WHO grade IV) (28, 40–42).