However, we did not find direct binding of PBX1 to the promoter region of RUNX2 and ALP in the ChIP assay, which implies that the expression changes of these two factors during the ossification process of OPLL may be due to the consequent regulation of other ossification master genes, such as OSX. The gene discussed is PBX1; the disease is ossification of the posterior longitudinal ligament of the spine.