[Vitamin D receptor gene polymorphism and the rate of bone loss of the femur neck and lumbar spine in hemodialized patients with chronic renal failure]. / Polimorfizm genu dla receptora witaminy D a szybkosc ubytku masy kostnej w zakresie szyjki kosci udowej i kregoslupa ledzwiowego u chorych na przewlekla niewydolnosc nerek leczonych hemodializami.

ABSTRACT

It has been suggested that the vitamin D receptor (VDR) gene Bsml-polymorphism is a genetic determinant of bone metabolism. 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 136 haemodialyzed patients. 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, bone alkaline phosphatase activity and intact 1, 84-PTH levels were measured. VDR genotype BB, Bb and bb were found in 24%, 46% and 30% of patients respectively. Initial BMD (g/cm2) of lumbar spine and femoral neck did not differ between genotypes, however the decrease of femoral neck BMD during 18 months of observation differ significantly (p < 0.02) between the particular genotype groups (femoral neck BB -0.031 +/- 0.029; Bb -0.027 +/- 0.017; bb -0.017 +/- 0.019 g/cm2). Significantly lower serum level of 25OHD3 was found in patients with the BB genotype before and after 18 months of observation in comparison to the respective values obtained in bb genotype patients, (respectively, 21.0 +/- 16.8 ng/ml vs 30.8 +/- 17.9 ng/ml; p < 0.01 and 24.0 +/- 10.8 ng/ml vs 32.4 +/- 16.0 ng/ml; p < 0.02). BB genotype patients were also characterised by significantly lower serum level of 1.25(OH)2D3 both initially and after 18 month of the study (respectively in BB and bb patients 25.9 +/- 9.7 pg/ml vs 30.7 +/- 10.0 pg/ml; p < 0.02 and 18.4 +/- 12.3 pg/ml vs 24.3 +/- 13.0 pg/ml; p < 0.01). No significant differences were found in Ca, P, osteocalcin, iPTH serum concentrations and bone fraction of alkaline phosphatase activity between particular genotypes. Results from this study suggest that faster bone mineral loss and more exaggerated disturbances of vitamin D metabolism are present in haemodialyzed uraemic patients with BB than bb genotype of VDR.