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. This evidence concerns the gene BMP4 and ossification of the posterior longitudinal ligament of the spine.