OPG rs2073617 polymorphism is associated with upregulated OPG protein expression and an increased risk of intervertebral disc degeneration

The present study aimed to investigate the associations between three distinct osteoprotegerin (OPG) gene polymorphisms and the risk of intervertebral disc degeneration (IDD). A total of 200 IDD patients and 200 healthy controls were recruited from the Department of Spine Surgery at the First Affiliated Hospital of the University of South China (Hengyang, China) between January 2013 and May 2014. The allele, genotype and haplotype frequency distributions of three OPG polymorphisms in the study and control populations were analyzed by polymerase chain reaction prior to restriction fragment length polymorphism or high resolution melting assays. In addition, serum OPG levels were measured via an ELISA. The genotype and allele frequencies of the OPG rs2073617 polymorphisms were significantly higher in the IDD patients, as compared with the control group (P < 0.05). Furthermore, carriers of the C allele exhibited a higher risk of IDD, as compared with carriers of the T allele (P < 0.001). Conversely, the genotype and allele frequencies of the two other gene polymorphisms, rs2073618 and rs3102735, showed no significant differences between the patients and controls (P > 0.05). The serum OPG levels were significantly higher in IDD patients with TT, TC and CC genotypes at the OPG rs2073617 polymorphism, as compared with the control group (P < 0.05). Logistic-regression analysis suggested that high serum levels of OPG were positively correlated with IDD risk, whereas the T-C-A, T-G-A and T-G-G haplotypes were negatively correlated with IDD risk (P < 0.05). Furthermore, the G-T-G haplotype was associated with protection against IDD (P = 0.008), whereas the G-C-G haplotype was associated with an elevated susceptibility to IDD (P = 0.007). The results of the present study suggested that OPG rs2073617 polymorphisms and upregulated serum levels of OPG were associated with an increased risk of IDD, whereas the T-C-A, T-G-A and T-G-G haplotypes were protective factors for IDD. The results of the present study suggested that the OPG gene polymorphism may have an important role in the progression of IDD, and its serum level may function as a valuable predictive indicator of the severity of degenerative disc diseases.