RUNX2 and ossification of the posterior longitudinal ligament of the spine: Single nucleotide polymorphisms (SNP) and mutations of various genes, including BMP-2, PTCH1, BMP4, TGF-β1, TGF-β3, COL6A1, NPP1 and RUNX2, have been associated with OPLL development, which indicates that genetic factors may play key roles in this process2–5.