COL2A1 and atrial fibrillation: Analysis of expression of traditional marker genes in human normal IVD samples (Figure 5) showed that when compared with AC cells, ACAN and COL2A1 gene expression was significantly lower in normal AF cells (P = 0.0003, and P < 0.0001, respectively) and normal NP cells (P = 0.0018, and P < 0.0001, respectively).