ALPL and ossification of the posterior longitudinal ligament of the spine: Relative gene expression analysis by quantitative real-time polymerase chain reaction (qRT-PCR) with SYBR Green showed that ALPL gene expression was initially higher in the OPLL group than in the Ctrl group, whereas BMP2, RUNX2, and COL1A2 mRNA levels showed little differences (Figure 1h–k).