ACE and ossification of the posterior longitudinal ligament of the spine: The single nucleotide polymorphisms (SNPs) of bone morphogenetic protein (BMP) 2, 4, and 9, collagen 6A1, angiotensin I converting enzyme gene, BH3 interacting domain death agonist, nucleotide pyrophosphatase, and vitamin K epoxide reductase complex subunit 1 are significantly associated with the occurrence and development of OPLL [4–9].