COMP and intervertebral disk degenerative disorder: COMP and CTX‐II, a degradation product of collagen II, are known markers of IDD and serve as blood biomarkers of IDD.[64] Interestingly, an upregulation of COMP was identified in Col IX‐deficient mice that developed IDD with age[65] while we found next to the significant increase of COMP level also an upregulation of Col IX in the DAC in human IVD.