IDH2 and neoplasm: The IDH1/2 mutations are confined to defined gene hotspots and affect either arginine 132 (R132) in IDH1 or arginines R172 or R140 in IDH2. Although IDH1/2 mutations are confined to these three hotspots, several reports have shown that the IDH-mutation spectrum differs per tumour type [12, 15, 20, 37].