GDF2 and ossification of the posterior longitudinal ligament of the spine: Four genes within this family of growth factors have been associated with both altered susceptibilities to bony spinal pathology and altered susceptibility to the development of myelopathy: BMP2, BMP4, BMP9, and BMPR1A. The 4A>C SNP in the BMPR1A gene is associated with a significantly greater likelihood of radiological OPLL and a significantly greater number of ossified vertebrae [27].