A particular subgroup of gliomas carrying mutation(s) in the IDH1/2 gene (IDH-mut) express the CpG island methylation phenotype (GCIMP), which is characterized by large-scale hypermethylation patterns mainly due to the oncometabolic repression of demethylating enzymes such as the Tet-type DNA-methylases but also selected histone modifiers. The gene discussed is IDH1; the disease is central nervous system cancer.