IDH1 and oligoastrocytoma: IDH-mutant tumors across all histopathologic subtypes of lower-grade glioma (LGG, i.e. WHO grade-II and -III oligodendrogliomas, oligoastrocytomas and astrocytomas) were strongly associated with the risk-allele of rs55705857 (ORs of 10.55, 9.41 and 8.91; n = 67, 32, 38, respectively; all p < 0.0001) (Supplementary Table 2).