In isocitrate dehydrogenase (IDH) mutant glioma cells (a gain-of-function mutation catalyzing the production of 2-hydroxyglutarate (2HG)), 2HG inhibits α-ketoglutarate-dependent dioxygenases and consequently reduces TET demethylase activities and increases genomic DNA methylation. The gene discussed is IDH3A; the disease is central nervous system cancer.