Numerous studies have shown that BMP2 stimulates osteoblast differentiation in human stem cells [16], cultured rat calvarial osteoblasts [17], ST2 bone marrow stromal cell lines [18], SaOS-2 cells [19] and also OPLL cells [20], leading to the notion that it is involved in the etiology of OPLL development. Here, BMP2 is linked to ossification of the posterior longitudinal ligament of the spine.