The assembly of this transcriptional complex is controlled by BMPs, and the deficiency of BMPs in IDD patients caused the impaired assembly of pSmad1/5/8-Smad4, thus decreasing the transcriptional efficiency of the whole pSmad1/5/8-HDAC1-Smad4 complex. The gene discussed is SMAD4; the disease is intervertebral disk degenerative disorder.