IDH1 and central nervous system cancer: IDH1 mutations in codon R132 are the predominant IDH mutations in brain tumors; these mutations are functionally similar to R172 mutations in IDH2. IDH1 R132H mutations represent ~90% of all glioma-associated IDH mutations; IDH1 R132C, R132S, R132G, and R132L, as well as IDH2 R172K, R172M, and R172W represent the remaining 10%.