Influence of Bsml vitamin D receptor gene polymorphism on the response to a single bolus of calcitriol in hemodialysis patients

Aims: BsmI polymorphism of the vitamin D receptor gene has been linked to h yperparathyroidism severity and calcitriol levels. The aim of this study wa s to analyze the response to a single bolus of calcitriol in hemodialysis p atients with the BB and bb genotype. Patients: Twenty homozygous BsmI hemod ialysis. patients (9 BB and 11 bb). Methods: Hyperparathyroidism was assess ed comparing basal PTH levels, and in 17 patients, also measuring the inhib ition with hypercalcemia. Patients were given a bolus of calcitriol and PTH in absolute terms and in percentages relative to the baseline values at 24 , 48 and 72 hours after the bolus were measured. All biochemical parameters were compared between genotypes with univariant ANOVA and additionally, PT H relative values were compared with general factorial analysis of variance , adjusting for calcium and phosphorus. Means were also compared within eac h genotype between consecutive determinations with non-parametric Wilcoxon analysis, using each patient as his/her own control. The response to calcit riol was also assessed by the area under the curve for each patient and was subsequently compared between genotypes. Results: There were no difference s on hyperparathyroidism severity between the groups. The BB genotype showe d a better response than bb to calcitriol 72 hours after the bolus (percent age relative to basal PTH value: BB: 63%, bb: 88.6%, p = 0.03; BB vs. bb wi th univariant ANOVA). When general factorial analysis of variance was appli ed, adjusting for serum calcium and phosphorus, genotype showed a significa nt influence on the response to calcitriol at 72 hours (p = 0.04). When eac h patient was used as his/her own control, the BB genotype showed a signifi cant decrease in PTH levels at 48 and 72 hours (p = 0.00 baseline vs 48 h, and p = 0.01 baseline vs 72h) whereas the bb did not. Conclusions: BsmI pol ymorphism of the VDR gene induces differences on the response to a single b olus of calcitriol independently of calcium and phosphorus.