IDH1 and glioma: Of the 417 grade II gliomas examined, mutations at codon 132 of the IDH1 gene were detected in 309 tumors (74%) including 304 R132H mutations (arginine to histidine substitution [CGT to CAT]) and 5 R132G mutations (arginine to glycine substitution [CGT to GGT]), which resulted in amino acid sequence alterations.