IDH1 mutations in gliomas are gain-of-function mutations that lead to the generation of the oncometabolite 2-hydroxyglutarate instead of 2-oxoglutarate from isocitrate, which induces a wide range of epigenetic dysregulation collectively termed “glioma CpG island methylator phenotype” [144]. The gene discussed is IDH1; the disease is central nervous system cancer.