In the microarray assay, inspection of the common genes altered in grade II to IV IVD degenerative specimens revealed five EGF receptor ligand genes that were increased two-fold in NP cells (EGF, EPGN, EREG, AREG and TGFA) but only two genes in AF cells (EPGN and HBEGF) (Fig. 4A). This evidence concerns the gene EPGN and atrial fibrillation.