IDH1 and neoplasm: IDH2 encodes for the mitochondrial NAD(+)-dependent isocitrate dehydrogenase which is involved in the citric acid cycle.43 While IDH2 p.(Arg261His) is not mutated in glioma, IDH1 or IDH2 are commonly mutated in glioma tumours and always involve the arginine residue.44IDH2 is in chromosome 15q26.1, the location of a previously reported glioma linkage peak.45 Modelling of the IDH2 p.(Arg261His) change is shown in Supplementary Figure 4.