As the proportion alterations of 11 cell types in grades II, III and IV are shown in Figure 1C, we can find that the proportion of metabolic homeostatic NP cells (Met NPC, 32.37%) was the highest at the early period (grade II) of disc degeneration, then the proportion of fibrocartilagenous NP cells (Fc NPC) increased at the middle (grade III, 40.64%) and late (grade IV, 31.11%) period of disc. This evidence concerns the gene NPC1 and intervertebral disk degenerative disorder.