PPM1D and glioma: Susceptibility to NAMPT inhibitors was particularly noted in epithelial-to-mesenchymal transition (EMT)-subtype gastric cancers, in isocitrate dehydrogenase 1 (IDH1)-mutant gliomas, and in protein phosphatase Mg2+/Mn2+-dependent 1D (PPMD1)-mutant gliomas as a result of the epigenetic loss of the NAPRT gene expression that frequently accompanies these cancer subtypes [29,30,31].