Unsupervised cluster analysis of 1122 grade II-III-IV gliomas from The Cancer Genome Atlas (TCGA) identified six methylation groups (LGm1–6) that were in part associated with IDH status and further discovered an epigenetic signature that segregated a subgroup of IDH-mutant diffuse lower-grade gliomas with unfavorable clinical outcome (Ceccarelli et al., 2016). Here, IDH1 is linked to glioma.