Recurrent heterozygous mutations in the isocitrate dehydrogenase 1 (IDH1) enzyme are very common in grade II-III glioma and secondary glioblastoma1,2, which now are recognized in the 2016 World Health Organization classification of central nervous system tumors3 to be a particular subtype of glioma characterized by the distinct molecular and clinical phenotypes. The gene discussed is IDH1; the disease is glioma.