The polymorphism in intron 6 (-4A) seems to confer protection to OPLL furthermore, it was proven that this polymorphism of COL11A2 affects the splicing of exon 6 in cells obtained from spinal ligaments from OPLL patients (Maeda et al., 2001b). The gene discussed is COL11A2; the disease is ossification of the posterior longitudinal ligament of the spine.