PER2 and glioma: Gao et al. (Gao et al., 2021) observed that IDH1 gene mutations in gliomas significantly reduced PER genes expression (PER1, PER2, and PER3) and altered the expression of cell cycle-related proteins like Cyclin A, CDK2, and Cyclin D3, resulting in increase of G1 phase cells and decrease of S phase cells.