COL11A2 and ossification of the posterior longitudinal ligament of the spine: The previous study demonstrated that patients with OPLL had a significantly higher incidence of genetic abnormalities in the type XI collagen (alpha) 2 gene (COL11A2) region25, and genome-wide linkage study showed that a single-nucleotide polymorphism in the collagen 6A1 gene (COL6A1) was strongly associated with OPLL26.