Recently, a genome-wide association study of OPLL patients identified RSPO2, which encodes R-spondin 2, as a susceptibility gene for OPLL; notably, R-spondin 2 is a secreted agonist of canonical Wnt–β-catenin signaling and is reduced in early stages of chondrocyte differentiation16. The gene discussed is RSPO2; the disease is ossification of the posterior longitudinal ligament of the spine.