EFFECT OF VITAMIN-D-RECEPTOR GENOTYPES ON CALCIUM-ABSORPTION, DUODENAL VITAMIN-D-RECEPTOR CONCENTRATION, AND SERUM 1,25-DIHYDROXYVITAMIN-D LEVELS IN NORMAL WOMEN

It is well established that bone mineral density is under strong genet ic control. Recently it was reported that the Bsm I restriction fragme nt length polymorphism of the vitamin D receptor (VDR) gene could acco unt for up to 75% of the genetic variance in bone mineral density. How ever, the physiological basis for such an effect has not been establis hed. The VDR gene codes for the vitamin D receptor protein which regul ates intestinal calcium absorption. In order to assess the biochemical basis we studied the effect of common allelic variation of the VDR ge ne on intestinal VDR protein concentration, calcium absorption, and se rum 1,25 dihydroxyvitamin D (1,25(OH)(2)D). Ninety-two Caucasian women were genotyped for Bsm I and Tag I polymorphism at the VDR gene locus . From these we compared 49 young women aged 25-35 years and 43 elderl y women aged 65-83 years, who had all three measurements performed. Th ere were no significant differences in intestinal VDR protein concentr ation, serum 1,25(OH)(2)D, or radioactive calcium absorption among VDR genotype groups. Therefore, the small intestine does not seem to be a target for VDR gene polymorphism.