IDH1 and glioblastoma: Consequently, there has only been a few reports on specific gene expression profiling of IDH1-mutant GBM in comparison with that of the IDH1-wildtype GBM, although the IDH1 mutation in glioma has been found to cause extensive DNA hypermethylation (glioma CpG island methylator phenotype, G-CIMP) leading to the suppression of gene expression [20].