A NP/AF gene expression ratio of around 10 has been reported in beagle tissue [23], beagles proving a good model of human disc degeneration as they lose their notocordal cell population as the young adult ages; conversely, a microarray study noted no difference in NCAM1 expression between human NP and AF tissues [48]. The gene discussed is NCAM1; the disease is intervertebral disk degenerative disorder.