Vitamin D Receptor Genotypes and Intestinal Calcium Absorption in Postmenopausal Women

Abstract.

Several studies have shown that bone mass and bone turnover are genetically determined. This genetic component is thought to be mediated in part by polymorphisms at the vitamin D receptor (VDR) locus, even though the underlying molecular mechanisms are still unknown. To evaluate a possible site of differential action of the VDR gene alleles we examined their correlation with intestinal calcium absorption in 120 Caucasian postmenopausal women (aged 61 ± 0.6 years). VDR gene polymorphisms for Apa I, Bsm I, and Taq I restriction endonucleases were assessed by Southern blotting analysis. The most common genotypes observed in our population were AaBbTt (37%), AABBtt (20%), aabbTT (15%), AabbTT (15%), and AABbTt (9%). Although there was some evidence of 13% higher lumbar BMD values in aabbTT genotype with respect to AABBtt genotype, this difference of approximately 0.1 g/cm² did not reach statistical significance, possibly because of the limited number of observations. On the contrary, no relationship was found between genotypes and femoral neck BMD values. Intestinal calcium absorption was significantly lower in BB and tt genotypes than, in bb and TT genotypes, respectively, and in AABBtt genotype than in either aabbTT or AaBbTt genotypes (P= 0.0015 ANOVA). No significant differences in intact PTH, alkaline phosphatase, 25OHD₃, and 1,25(OH)₂D₃ were found among subjects with different VDR genotypes. These results are consistent with a possible role of VDR alleles on intestinal calcium absorption.