Plasma parathyroid hormone, phosphatemia and vitamin D receptor genotype: are they interrelated?

It is not clear how the rate of bone mineral loss and vitamin D receptor (V DR) Bsml polymorphism in hemodialysed patients are related. We therefore an alysed the relationships between indices of calcium-phosphate metabolism in respect to VDR genotype in 180 hemodialysed patients. We measured plasma c oncentrations of calcium, phosphate, iPTH, 1,25(OH)(2)D-3 and activity of t he bone fraction of alkaline phosphatase on the day before dialysis. VDR ge notype BB, Bb and bb were found in 39, 84 and 57 patients, respectively. Th e allele frequency was B 0.45 and b 0.55. Subjects with BE genotype had ins ignificantly higher plasma levels of phosphate, iPTH and activity of the bo ne fraction of alkaline phosphatase, but significantly lower (p<0.02) conce ntrations of 1,25(OH)(2)D-3 [iP (mmol/l): 2.05+/-0.09, 1.98+/-0.06, 1.93+/- 0.06; iPTH (pg/ml): 257+/-50, 229+/-24, 219+/-30; AP(BF) (nmol/l/s): 515+/- 45, 477+/-27, 457+/-34; 1,25(OH)(2)D-3 (pg/ml): 23.4+/-1.5, 26.2+/-1.0, 29. 3+/-1.3, for BE, Bb and bb respectively]. The strongest significant correla tion between phosphatemia and iPTH was in the BE subgroup (r=0.343). Moreov er, only in this subgroup did phosphatemia significantly contribute to the increase in iPTH, assessed by multiple regression analysis. In conclusion, it seems likely that BE VDR genotype in HD patients contributes to the seve rity of secondary hyperparathyroidism by a mechanism involving phosphatemia .