The plasma concentration of COL6A1 was shown in Fig. 1; plasma COL6A1 concentration was significantly higher (~ 3-fold higher) in T-OPLL patients with rs201153092A mutation (20.90 ± 0.64 μg/l) compared with T-OPLL patients carrying the wild-type rs201153092G variant (4.79 ± 1.1 μg/l, P < 0.001). Here, COL6A1 is linked to ossification of the posterior longitudinal ligament of the spine.