Does the vitamin D receptor genotype predict bone mineral loss in haemodialysed patients?

Background. It has been suggested that the vitamin D receptor (VDR) gene BsmI-polymorphism is a genetic determinant of bone metabolism. Design. To test this hypothesis, the relationship between VDR genotypes, bone mineral density (baseline and after 18 months) and parameters of calcium metabolism and bone turnover were investigated prospectively in 88 haemodialysed patients not receiving active vitamin D metabolites. Methods. Whole body, lumbar spine and femoral neck bone mineral density (BMD) were assessed by dual energy X-ray absorptiometry (DEXA). In addition calcium, phosphorus, 25(OH)D3, 1,25(OH)2D3, osteocalcin serum concentrations, alkaline phosphatase activity and intact, 1,84 PTH levels were measured. Results. VDR genotype BB, Bb and bb were found in 27, 49 and 24% of patients. Initial BMD (g/cm²) of whole body, lumbar spine and femoral neck did not differ between genotypes (whole body: BB 1.055 ± 0.120, Bb 1.082 ± 0.102, bb 1.128 ± 0.120; lumbar spine: BB 1.075 ± 0.199, Bb 1.079 ± 0.185, bb 1.099 ± 0.170; femoral neck: BB 0.808 ± 0.160, Bb 0.862 ± 0.127, bb 0.842 ± 0.125; mean ± SD), but the decrease of whole body and femoral neck BMD during 18 months was significantly (P < 0.02) different between the genotype groups (whole body: BB -0.048 ± 0.028, Bb -0.031 ± 0.029, bb -0.024 ± 0.023; femoral neck BB -0.044 ± 0.069, Bb -0.032 ± 0.081, bb -0.012 ± 0.029 g/cm²). Conclusions. This preliminary study suggests faster mineral loss in BB genotype of VDR in haemodialysed patients.