Analysis of vitamin D-binding protein (VDBP) gene polymorphisms in Korean women with and without endometriosis

Objective: Vitamin D-binding protein (VDBP) mediates various biological processes in humans. The goal of this study was to investigate whether VDBP gene polymorphisms could predispose Korean women to endometriosis. Methods: We prospectively enrolled women with endometriosis (n=16) and healthy controls (n=16). Total serum 25-hydroxyl vitamin D (25(OH) D) concentrations were measured using an Elecsys vitamin D total kit. Levels of bioavailable and free 25(OH) D were calculated. Concentrations of VDBP were measured using a vitamin D BP Quantikine ELISA kit. DNA was extracted using a DNeasy blood & tissue kit. Two single-nucleotide polymorphisms (SNPs; rs4588 and rs7041) in GC, the gene that codes for VDBP, were analyzed using a TaqMan SNP genotyping assay kit. The functional variant of VDBP was determined based on the results of the two SNPs. Results: Gravidity and parity were significantly lower in the endometriosis patients than in the control group, but serum CA-125 levels and the erythrocyte sedimentation rate were significantly higher. Total serum 25(OH) D levels in the endometriosis patients were significantly lower than in the control group. However, serum bioavailable 25(OH) D, free 25(OH) D, and VDBP levels did not differ significantly between the endometriosis and control groups. The genotypes and allele frequencies of GC were similar in both groups. Conclusion: Korean women with endometriosis had lower total serum 25(OH) D concentrations than controls. Neither serum VDBP concentrations nor polymorphisms in the gene coding for VDBP were associated with endometriosis. Further studies are needed to investigate the pathophysiology and clinical implications of 25(OH) D and VDBP in endometriosis.