IDH2 and glioma: IDH1/2 mutations should arise during embryonic development due to the somatic mosaic of mutant IDH1/2-expressing cells, such as IDH1 R132H/C/L/S or R100Q and IDH2 R140Q/G/W/L or R172K/G/M/Q/T/S, which are common mutations in gliomas (bold are the most frequent) (20, 180).