To assess the relationship between two genes and the WHO grade, chi-square test of the original data from TCGA and CGGA revealed that abnormally high mRNA expression of Per2 was negatively correlated with the WHO grade, while high mRNA expression of Id3 was positively correlated with the WHO grade in patients with glioma (Figure 1a, FigureS1a). The gene discussed is PER2; the disease is central nervous system cancer.