IDH1 and central nervous system cancer: We suggest that thresholds can be defined in the differences between the AB and FS models (AB-FS) in the amide and in the amine ranges, to divide the IDH-mutant_1p/19qret gliomas in two subgroups: with and without AB/FS mismatch (thresholds: AB-FS (∆3.5) = 0.039 and AB-FS (∆2) = 0.18).