QUANTIFICATION OF VITAMIN-D-RECEPTOR MESSENGER-RNA BY COMPETITIVE POLYMERASE-CHAIN-REACTION IN PBMC - LACK OF CORRESPONDENCE WITH COMMON ALLELIC VARIANTS

It has been recently claimed that polymorphism for the vitamin D recep tor (VDR) influences several aspects of calcium and bone metabolism, T o evaluate the physiologic plausibility of these claims, we compared t he abundance of the VDR mRNA in peripheral blood mononuclear cells (PB MCs) between different VDR genotypes using a quantitative reverse tran scribed polymerase chain reaction-based method, The method is based on the coamplification of VDR cDNA and an internal standard consisting o f known concentrations of a human VDR CDNA mutated at a Bg/II restrict ion site; the interassay coefficient of variation is 11%, To validate the method, we made use of earlier receptor binding studies indicating that normal human monocytes and activated, but not resting, lymphocyt es expressed the VDR, The concentration of the VDR mRNA was 10(-8) to 10(-7) g/g of total RNA in cell-sorted monocytes and in in vitro activ ated lymphocytes, but only 10(-12) g/g of total mRNA in resting lympho cytes, establishing that the VDR mRNA determined by our method in PBMC s is due to constitutive expression in monocytes, Following an initial genotype screening of 85 normal volunteers by polymerase chain reacti on or restriction fragment length polymorphism analysis, 14 individual s with the Bb genotype, 12 with the bb genotype, and 12 with the BB ge notype were selected, The concentration of the VDR mRNA, corrected for the number of monocytes, was similar among the three genotype groups, as were the other variables examined: serum calcitriol, serum osteoca lcin, and vertebral and hip bone density, We conclude that VDR polymor phism does not affect the abundance of the VDR mRNA.