COL6A1 and ossification of the posterior longitudinal ligament of the spine: In the present study, we examined all 11 reported OPLL-associated genes, and identified for the first time eight deleterious variants in four genes (COL6A1, COL11A2, FGFR1 and BMP2), which significantly expanded our understanding of the mutation spectrum of OPLL and the nature of the gene function as we showed in the context.