IL17RC and ossification of the posterior longitudinal ligament of the spine: The plasma concentration of IL17RC was shown in Fig. 2; plasma IL17RC concentration was significantly higher (~ 3-fold higher) in T-OPLL patients with rs199772854A mutation (9.91 ± 1.91 μg/l) compared with T-OPLL patients carrying the wild-type rs199772854C variant (3.34 ± 0.69 μg/l; P < 0.01).