The differential expression of CCGs in glioma grading confirmed that cluster I genes (ARNRL, NPAS2, and TIMELESS) and CRY1, with cluster II genes (CRY2, DBP, NR1D1, NR1D2, PER2, PER3, and RORA) showed significantly opposite expression trends in brain tissues (Figure 3). The gene discussed is NR1D1; the disease is glioma.