Relationship between glucocorticoid-induced osteoporosis and vitamin D receptor genotypes

By means of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay, the association between vitamin D receptor (VDR) genotypes and bone mineral density (BMD) in the patients receiving long-term glucocorticoid therapy was studied. The clinical data and blood of 71 patients with rheumatosis who received long-term glucocorticoid therapy were collected. BMD was measured by dual-energy X-ray absorptimometry. VDR gene fragment (about 185 bp) was amplified by PCR from the extracted genomic DNA, then digested with restriction endonuclease Bsm I. The genotypes were evaluated based on the fragment length following endonuclease digestion and the association between genotypes and BMD or Z-score values was analyzed. Among the 71 cases, the detected genotypes were Bb and bb with the distribution frequency being 11.3% and 88.7% respectively. The distribution frequency of the alleles was in agreement with the Hardy-Weinberg equilibrium. There was no significant difference between the two genotypes in age, gender, body mass index (BMI), disease duration, disease types, time of glucocorticoid administration and cumulative dosage (P > 0.05). Osteoporosis rate of the patients with Bb or bb genotype was 37.5% and 33.3% respectively, with the difference being not significant (chi 2 = 0.05, P = 0.8). The BMD and Z-score values at lumbar spine and femur in two genotypes were not similar, but the difference had no significant (P > 0.05). The distribution frequency of bb type of VDR genotypes in Han populations of China was more prevalent, followed by Bb and bb types in turn. In the patients receiving long-term glucocorticoid therapy, there was no significant difference in BMD between Bb and bb genotypes. The data suggest that the VDR genotypes may not be means of identifying patients at greater risk of glucocorticoid-induced osteoporosis, which await to be further confirmed by a large sample size.