CDKN2A and central nervous system cancer: Furthermore, we observed that IDH1R132H expression was markedly decreased in tumors but became more permissible upon the deletion of tumor-suppressor gene Cdkn2a. To provide direct evidence for the opposing effect of IDH1R132H on PDGFB-driven glioma development, we explored tandem expression of the two molecules from a single transcript to preclude selection against IDH1R132H expression.