Background: Some polymorphisms at the human vitamin D receptor (VDR) gene locus may influence calcium and bone metabolism. We investigated the roles of the BsmI and TaqI VDR gene polymorphisms in the development of hypercalcemia in Turkish peritoneal dialysis (PD) patients.
Methods: We enrolled 132 PD patients treated with dialysate containing 1.75 mmol/L calcium. Serum levels of calcium, phosphorus, albumin, and intact parathyroid hormone (iPTH), and the cumulative doses of calcium-based phosphate binders and calcitriol were recorded every 3 months. The VDR BsmI and TaqI genotypes were determined by polymerase chain reaction.
Results: When the patients were categorized according to these VDR genotypes, serum levels of phosphorus and iPTH and cumulative doses of calcium-based phosphate binders and calcitriol were similar across groups. The corrected serum calcium levels tended to increase in the patients with BsmI non-BB (Bb + bb) variants, but were significantly decreased in the BB variants (9.9 +/- 0.7 vs 9.1 +/- 0.6 mg/dL, p < 0.05). Hypercalcemia appeared in 21.2% of the patients during the follow-up period. The hypercalcemic patients had a significantly higher prevalence of the BsmI non-BB genotype than the normocalcemic patients (85.7% vs 59.6%, p < 0.007). On the contrary, the serum calcium levels were not affected by the TaqI VDR gene polymorphism (p > 0.05).
Conclusions: These findings suggest that the non-BB variants of the BsmI VDR gene polymorphism are associated with increased risk of developing hypercalcemia in PD patients.