Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu1, J. C. Gallagher1, J. A. Knezetic2, H. F. DeLuca4, J. M. Prahl4, S. J. Lanspa3 1Bone

Metabolism Unit, Creighton University School of Medicine, 601 N. 30th Street, Omaha, Nebraska 2Department of Biomedical Sciences, Creighton University School of Medicine, 601 N. 30th Street, Omaha, Nebraska 3Department of Gastroentrology, Division of Digestive Diseases, Creighton University School of Medicine, 601 N. 30th Street, Omaha, Nebraska 68131 4Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53703 Received: 12 August 1996 / Accepted: 3 January 1997 Key words: VDR genotypes - Calcium absorption - Duodenal VDR - 1,25 dihydroxyvitamin D. Correspondence to: J. C. Gallagher

Contents ● ● ● ● ● ●

Abstract Introduction Materials and Methods Results Discussion Acknowledgments

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Tables (in a separate window) ●

Table 1

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Figure 1

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa To: Article contents, Introduction, Materials and Methods, Results, Discussion, Acknowledgments, References

Abstract

It is well established that bone mineral density is under strong genetic control. Recently it was reported that the Bsm I restriction fragment length polymorphism of the vitamin D receptor (VDR) gene could account for up to 75% of the genetic variance in bone mineral density. However, the physiological basis for such an effect has not been established. The VDR gene codes for the vitamin D receptor protein which regulates intestinal calcium absorption. In order to assess the biochemical basis we studied the effect of common allelic variation of the VDR gene on intestinal VDR protein concentration, calcium absorption, and serum 1,25 dihydroxyvitamin D (1,25(OH)2D). Ninety-two Caucasian women were genotyped for Bsm I and Taq I polymorphism at the VDR gene locus. From these we compared 49 young women aged 25-35 years and 43 elderly women aged 65-83 years, who had all three measurements performed. There were no significant differences in intestinal VDR protein concentration, serum 1,25(OH)2D, or radioactive calcium absorption among VDR genotype groups. Therefore, the small intestine does not seem to be a target for VDR gene polymorphism. To: Article contents, Introduction, Materials and Methods, Results, Discussion, Acknowledgments, References

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa To: Article contents, Abstract, Materials and Methods, Results, Discussion, Acknowledgments, References

Introduction

Recently, there have been reports of an association between bone mineral density and vitamin D receptor genotypes. Results from a twin study in Australia suggested that Bsm I polymorphism within the gene encoding for the vitamin D receptor (VDR) could be used to predict up to 75% of total genetic variance on bone density in healthy individuals [1]. Since then, some studies, genetic or population based, have confirmed this finding [2-6] but others have not [7, 8]. In type I osteoporotics no association between VDR genotypes and bone mineral density has been demonstrated [9-12]. The polymorphism described by Morrison et al. [1] is within the 3' untranslated region (3-UTR) and the intronic sequences of the VDR gene, suggesting that there would be no differences within genotypes in the expressed VDR protein. In an attempt to derive the biochemical basis of the VDR gene polymorphism effect on bone mass, the authors conducted minigene in vitro experiments by linking sequences from the 3' UTR of two common genotypes (BBAAtt and bbaaTT) with respect to Bsm I, Taq I, and Apa I polymorphism to reporter genes. The minigene representing BBAAtt increased reporter gene activity, suggesting that this genotype expressed higher VDR mRNA and VDR protein concentration. With this in mind, we investigated the effect of common VDR gene polymorphisms on duodenal VDR protein concentration and calcium absorption. We hypothesized that the allelic variation of the VDR gene could influence bone mass through changes in calcium absorption, mediated by changes in duodenal VDR protein concentration and changes in serum 1,25(OH)2D levels. http://link.springer.de/link/service/journals/00223/papers97/60n6p491/sec01.html (1 of 2) [2/4/2003 6:40:00 PM]

Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa To: Article contents, Abstract, Introduction, Results, Discussion, Acknowledgments, References

Materials and Methods

Subjects Vitamin D receptor gene polymorphism with respect to Bsm I and Taq I restriction endonucleases was determined on 92 Caucasian women aged 25-83 years. Forty-nine women were young, mean 30 ± 3 years (range 25-35) and forty-three were elderly, mean 71 ± 5 years (range 65-83). Subjects had been recruited through newspaper advertisements and mass mailing of letters. Volunteers with medications or disorders thought to influence calcium or phosphorus homeostasis were excluded. Medication exclusions included those on hormone regimes including oral contraceptive pills, anticonvulsants, diuretics, corticosteroids, fluoride, bisphosphonates, and/or oral calcium or vitamin D supplements. The protocol was reviewed and approved by Creighton University Institutional Review Board. Dietary Intake Dietary calcium intake was calculated by a dietician from 4-or 7-day food diaries using the Food Processor II Plus Nutrition and Diet Analysis System, version 5.1 (Esha Research, Salem, OR). Calcium Absorption Test http://link.springer.de/link/service/journals/00223/papers97/60n6p491/sec02.html (1 of 3) [2/4/2003 6:40:01 PM]

Calcified Tissue International 60, 491 (1997)

Calcium absorption was measured in a fasting state by oral administration of 5 µCi of 45Ca with either a small calcium carrier of 20 mg or a larger carrier of 100 mg given as calcium chloride (CaCl2) in a total of 250 ml distilled water [13]. Subjects underwent both tests within 7-14 days of each test. Blood samples were collected at 1 hour for the 20 mg test and at 2 and 3 hours for the 100 mg test. 45Ca activity was counted in 2 ml of serum using the 1900 CA Tricarb Liquid Scintillation Analyzer (Packard Instrument, Meriden, CT). A parallel standard taken from the patients' dose cups before ingestion was counted at the same time as the sample. Calcium absorption was expressed as percent actual dose per liter of blood (%AD/L) and corrected for body mass index (BMI). The 3 h value is reported for the 100 mg test. Subjects weight and height were measured and BMI was calculated as weight/height2. Vitamin D Receptor Biopsy A biopsy sample (approximately 4 mg) was taken from the third portion of the duodenum under direct vision using a gastroendoscopic tube. Samples were quick frozen in plastic bags in liquid nitrogen, stored at -70oC, and shipped on dry ice to Wisconsin for VDR analysis. Vitamin D Receptor Analysis The concentration of VDR protein (femtomoles per mg mucosal protein) was measured by an immunoradiometric assay [14] which measures total VDR, and includes denatured, occupied, and unoccupied forms of the receptor. Biochemical Analysis Fasting blood samples were collected from each subject before the calcium absorption test. Blood specimens were allowed to clot, centrifuged, and the serum was separated. Serum samples were aliquoted and stored frozen at -70oC until analyzed. Serum 25 hydroxyvitamin D (250HD) was measured by a competitive binding assay [15] after chromatographic extraction and purification of serum on SepPak cartridges (Waters Associates, Milford, MA) [16]. The limit for detection for the assay is 5 ng/ml and the interassay variation is 5%. Serum 1,25(OH)2D was measured by a nonequilibrium radioreceptor assay (Incstar Corp., Stillwater, MN) using the calf thymus receptor after extraction and purification of the serum on nonpolar C18OH octadecysilanol silica cartridge [17, 18]. The limit of detection for the assay is 5 pg/ml and the interassay variation is 10%. VDR Gene Restriction Fragment Length Polymorphism (RFLP) DNA was isolated from white blood cells. Cells were collected by centrifugation and lysed in Triton X100 in 0.32 M sucrose, 10 mm Tris-HCl, pH 7.5, and 5 mm MgCl2. DNA was isolated by phenol/chloroform extraction, precipitated with 100% ethanol (-20oC), and dissolved in 10 mM Tris/1 mM EDTA (TE) buffer. To remove RNA, DNA samples were treated with RNase A, re-extracted with http://link.springer.de/link/service/journals/00223/papers97/60n6p491/sec02.html (2 of 3) [2/4/2003 6:40:01 PM]

Calcified Tissue International 60, 491 (1997)

phenol/chloroform, precipitated with 100% ethanol (-20oC), and dissolved in TE-buffer. Polymerase chain reaction (PCR) of the DNA sequence flanking the Bsm I and Taq I restriction sites of the VDR gene was performed using forward oligo primer 5'-CCA AGA CTA CAA GTA CCG CG-3' and reverse oligo primer 5'-TGA GGA GGG CTG CTG AGT AC-3'. The PCR product was digested using restriction endonuclease enzymes, Bsam I, which is an isoschizomer of Bsm I (Promega, Madison, WI) or Bsm I (New England Biolabs, Beverly, MA) and Taq I (New England Biolabs, Beverly, MA). Digestion reactions were set according to the manufacturers instructions. The digested product was fractionated using 2% agarose gel electrophoresis. Gels were stained with ethidium bromide, and visualized under UV light and photographed. The presence of a restriction site was genotyped as b allele and the absence of the restriction site was genotyped as B allele, for Bsm I site, and t and T for the Taq I site, respectively. The presence of (t) or absence of (T) on the Taq I polymorphic site is in linkage with absence of (B) or presence of (b), respectively, on the Bsm I polymorphic site. The PCR product was approximately 2035 bp. Homozygous absence of the B site or T site was seen as one band at 2035 bp. Homozygous site for Bsm I restriction site (bb) was seen as two bands at 1385 and 650 bp, and homozygous presence of the Taq I site (tt) was seen as two bands at 1917 and 118 bp. Statistical Analysis All analyses were performed by SPSS statistical program for windows. One-way analysis of variance (ANOVA) was used to examine the effects of common VDR gene polymorphism on calcium absorption, duodenal VDR protein concentration, and serum 1,25(OH)2D levels. We compared 49 young women and 43 elderly women who underwent all three measurements. Differences among genotypes were tested using Student Newman Keuls Multiple range test. Multivariate analysis of intestinal calcium absorption versus 1,25(OH)2D was performed on the 92 subjects with age group, vitamin D receptor concentration, serum 25OHD, calcium intake, and VDR genotype as independent variables. To: Article contents, Abstract, Introduction, Results, Discussion, Acknowledgments, References

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa To: Article contents, Abstract, Introduction, Materials and Methods, Discussion, Acknowledgments, References

Results

VDR Genotype Effects The frequency of VDR genotypes in the population studied was BBtt 24%, BbTt 50%, bbTT 26% (Table 1). The Bsm I restriction site showed a 99% association with the Taq I restriction site. Body weight, BMI, calcium intake, and serum 25OHD levels were similar among VDR genotypes in both the young and the elderly women. There was no relationship between the VDR genotypes and either of the calcium absorption tests, nor was there a relation between VDR genotypes and VDR protein concentration in the duodenum, nor with VDR genotypes and serum 1,25(OH)2D levels, in young or elderly women (Figs. 1, 2 and and 3). Serum 1,25(OH)2D was significantly correlated with 20 mg calcium absorption test in all subjects (r = 0.30, P < 0.004), in young subjects (r = 0.34, P < 0.02), and in the elderly subjects (r = 0.42, P < 0.005). Serum 1,25(OH)2D was not significantly correlated with 100 mg calcium absorption test in all subjects (r = 0.08), in young subjects (r = 0.12), or in elderly subjects (r = 0.21). In a multivariate analysis of intestinal calcium absorption (20- and 100-mg test) versus serum 1,25(OH)2D, the independent variables, age, VDR protein concentration, calcium intake, serum 250HD, and VDR genotype were entered into the model. Only age was a significant independent variable.

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa To: Article contents, Abstract, Introduction, Materials and Methods, Results, Acknowledgments, References

Discussion

Negative calcium balance resulting from malabsorption of calcium is one of the contributing causes to low bone mass, so that if allelic variation in the VDR affected bone density then one of the possible mechanisms might be through changes in calcium absorption. Since the vitamin D hormone 1,25(OH)2D regulates calcium absorption through the intestinal vitamin D receptor and because the VDR gene codes for the vitamin D receptor protein, it is possible that common VDR gene polymorphism could affect duodenal VDR protein concentration, serum 1,25(OH)2D, and calcium absorption. Our findings showed no association between allelic variation of the VDR gene and two tests of calcium absorption. The test with the small 20 mg calcium carrier probably measures active transport of calcium, whereas the larger 100 mg carrier measures both active and passive transport of calcium. Another study, in patients with absorptive hypercalciuria, did not show any association between VDR genotypes and those with increased intestinal calcium absorption, but they did not measure calcium absorption in any normal control group [19]. Another study of postmenopausal women, mean age 64 ± 8.4 years, showed no overall effect of VDR gene polymorphism on fractional calcium absorption, however, when statistical analysis was confined to nonhysterectomized women, calcium absorption was higher in women with TT(bb) compared with women with tt(BB) genotype [20]. It is possible that VDR gene polymorphism effects on calcium absorption could be masked by confounding factors such as calcium intake. In a study http://link.springer.de/link/service/journals/00223/papers97/60n6p491/sec04.html (1 of 3) [2/4/2003 6:40:07 PM]

Calcified Tissue International 60, 491 (1997)

of calcium absorption on high and low calcium intakes, calcium absorption was similar between genotypes at high calcium intake (1500 mg/day), but subjects with the BB genotype showed lower calcium absorption when placed on low calcium intake <300 mg/day [21]. One study has shown an association between VDR genotypes and the response in bone mineral density (BMD) to calcium supplements. In subjects on a low calcium intake, those with the BB genotype showed the largest change in BMD on calcium supplement [5]. Because of the small number of subjects in the low calcium intake group, further studies are needed to confirm this finding. There was no association between duodenal VDR protein concentration and the VDR genotypes in either young or older women. One other study found no differences in duodenal VDR protein concentration among VDR genotypes in young premenopausal women [22]. One might expect a functional system dependent on VDR protein concentration to show such genotype differences. However, it should be stressed that the immunoradiometric assay measures both occupied and unoccupied vitamin D receptors, and it is possible that the use of unoccupied VDR would be a more sensitive measure. Another model that might demonstrate functional genotype effects would be the expression of VDR in mononuclear cells and cultured skin fibroblasts. But vitamin D receptor mRNA concentration in peripheral blood mononuclear cells was similar among the VDR genotype groups [23]. In addition, a recent study, Gross et al. [24] observed no differences within genotype groups for VDR mRNA levels or VDR protein concentration from cultured skin fibroblasts. The lack of any differences in VDR protein concentration in our study is consistent with the fact that the Bsm I polymorphism is on the intronic site of the VDR gene and therefore unlikely to affect receptor protein concentration. We do not show any differences in serum 1,25(OH)2D levels among VDR genotypes. Higher serum 1,25(OH)2D levels in women with the BBtt genotype compared with women with the bbTT genotype have been reported by two groups [1, 25]. However, in the present study we found no difference in serum 1,25(OH)2D among the genotype groups. Our findings suggest that the biochemical basis by which common VDR gene polymorphism influences bone density is not through changes in calcium absorption or duodenal VDR protein concentration or serum 1,25(OH)2D levels. However, we cannot preclude the effect of VDR gene polymorphism on other genes related to calcium metabolism or the fact that VDR gene polymorphic effects might be specific to bone. To: Article contents, Abstract, Introduction, Materials and Methods, Results, Acknowledgments, References

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa To: Article contents, Abstract, Introduction, Materials and Methods, Results, Discussion, References

Acknowledgments

This work was supported by NIH Grants AG10358 and UO1-AG10373. To: Article contents, Abstract, Introduction, Materials and Methods, Results, Discussion, References

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa

References [Links are to the NCBI PubMed database of biomedical citations. Follow the link to view the citation and search for related articles.]

1. Morrison NA, Qi JC, Tokita A, Kelly PJ, Crofts L, Nguyen TV, Sambrook PN, Eisman JA (1994) Prediction of bone density from vitamin D receptor alleles. Nature 367: 284-287 2. Yamagata Z, Miyamura T, Lijima S, Asaka A, Sasaki M, Kato J, Koizumi K (1994) Vitamin D receptor gene polymorphism and bone mineral density in healthy Japanese women. Lancet I 344: 1027 3. Ferrari S, Rizzoli R, Chevalley T, Slosman D, Eisman JA, Bonjour JP (1995) Vitamin D receptor gene polymorphisms and change in lumbar-spine bone mineral density. Lancet II 345: 423-424 4. Spector TD, Keen RW, Arden NK, Morrison NA, Major PJ, Nguyen TV, Kelly PJ, Baker JR, Sambrook PN, Lanchbury JS, Eisman JA (1995) Influence of vitamin D receptor genotype on bone mineral density in postmenopausal women: a twin study in Britain. BMJ 310: 1357-1360 5. Krall EA, Parry P, Lichter JB, Dawson-Hughes B (1995) Vitamin D receptor alleles and rates of bone loss: influences of years since menopause and calcium intake. J Bone Miner Res 10(6): 978-984 6. Gallagher JC, Kinyamu HK, Knezetic JA, Ryschon KL (1996) Vitamin D receptor genes alleles and bone density in premenopausal women. J Bone Miner Res 11(S1): S210 7. Hustmyer FG, Peacock M, Hui S, Johnston CC, Christian J (1994) Bone mineral density in relation to polymorphism at the vitamin D receptor gene locus. J Clin Invest 94: 2130-2134 http://link.springer.de/link/service/journals/00223/papers97/60n6p491/refs.html (1 of 3) [2/4/2003 6:40:14 PM]

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8. Melhus H, Kindmark A, Amer S, Wilen B, Lindh E, Ljunghall S (1994) Vitamin D receptor genotypes in osteoporosis. Lancet I 344: 949-950 9. Gallagher JC, Goldgar D, Kinyamu H, Fannon P (1994) Vitamin D receptor genotypes in type I osteoporosis. J Bone Miner Res 9(S1): S143 10. Riggs BL, Nguyen TV, Melton J III, Morrison NA, O'Fallon WM, Kelly PJ, Egan KS, Sambrook PN, Muhs JM, Eisman JA (1995) The contribution of vitamin D receptor gene alleles to the determination of bone mineral density in normal and osteoporotic women. J Bone Miner Res 10: 991-996 11. Looney JE, Yoon HK, Fischer M, Farley SM, Farley JR, Wergedal JE, Baylink DJ (1995) Lack of a high prevalence of the BB vitamin D receptor genotype in severely osteoporotic women. J Clin Endocrinol Metab 80: 2158-2162 12. Lim SK, Park YS, Park JM, Song YD, Lee EJ, Kim KR, Lee HC, Huh KB (1995) Lack of association between vitamin D receptor genotypes and osteoporosis in Koreans. J Clin Endocrinol Metab 80: 36773681 13. Gallagher JC, Riggs BL, Eisman J, Hamstra A, Arnaud SB, DeLuca HF (1979) Intestinal calcium absorption and serum vitamin D metabolites in normal subjects and osteoporotic patients. J Clin Invest 64: 729-736 14. Sandgren ME, DeLuca HF (1989) An immunoradiometric assay for 1,25-dihydroxyvitamin D3 receptor. Anal Biochem 183: 57-63 15. Haddad JG, Chyu KJ (1971) Competitive protein-binding radioassay for 25-hydroxycholecalciferol. J Clin Endocrinol 33: 992-993 16. Reinhardt TA, Horst RL (1988) Simplified assays for the determination of 25-OHD, 24, 25-(OH)2D and 1,25-(OH)2D. In: Norman AW, Schaefer K, Grigoleit H-G, Herrath DV (eds) Vitamin D, molecular, cellular and clinical endocrinology. Walter de Gruyter & Co, Berlin-New York, pp 720-726 17. Reinhardt TA, Horst RL, Orf JW, Hollis BW (1984) A microassay for 1,25-dihydroxyvitamin D not requiring high performance liquid chromatography: application to clinical studies. J Clin Endocrinol Metab 58: 91-98 18. Hollis BW (1986) Assay of circulating 1,25-dihydroxyvitamin D involving a novel single-cartridge extraction and purification procedure. Clin Chem 32(11): 2060-2063

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19. Zerwekh JE, Hughes MR, Reed BY, Breslau NA, Heller HJ, Lemke M, Nasonkin I, Pak CYC (1995) Evidence for normal vitamin D receptor messenger ribonucleic acid and genotype in absorptive hypercalcuria. J Clin Endocrinol Metab 80: 2960-2965 20. Hayes JG, Nguyen TV, Need AG, Morrison NA, Kelly PJ, Morris HA (1995) Vitamin D receptor genotypes and fractional gut calcium absorption. J Bone Miner Res 10(S1): P237 21. Dawson-Hughes B, Harris SS, Finneran S (1995) Calcium absorption on high and low calcium intakes in relation to vitamin D receptor genotype. J Bone Miner Res 10(S1): S162 22. Barger-Lux MJ, Heaney RP, Hayes J, DeLuca JF, Johnson ML, Gong G (1995) Vitamin D receptor gene polymorphism, bone mass, body size, and vitamin D receptor density. Calcif Tissue Int 57: 161-162 23. Mocharla H, DeTogni P, Yu XP, White P, Jilka RL, Manolagas SC (1994) In search of an association between vitamin D3 receptor (VDR) polymorphism and VDR mRNA expression in peripheral blood mononuclear cells (PBMC) of normal volunteers. J Bone Miner Res 9(S1): S416 24. Gross C, Musiol I, Eccleshall R, Malloy PJ, Feldman D (1995) Vitamin D receptor (VDR) alleles: study of VDR expression and function in cultured human skin fibroblasts. J Bone Miner Res 10(S1): S162 25. Howard G, Nguyen T, Morrison N, Watanabe T, Sambrook P, Eisman J, Kelly PJ (1995) Genetic influences on bone density: physiological correlates of vitamin D receptor gene alleles in premenopausal women. J Clin Endocrinol Metab 80: 2800-2805

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa

Table 1. Descriptive data of two age groups by VDR Genotype

VDR genotypes Variable

Age

BBtt

BbTt

bbTT

Frequency N

25-35 >65

24% 14 8

50% 23 23

26% 12 12

Weight (kgs), mean

25-35

65 ± 9

63 ± 9

67 ± 9

>65

72 ± 7

69 ± 12

70 ± 10

25-35

24 ± 3

24 ± 3

23 ± 3

>65

28 ± 2

27 ± 4

27 ± 3

25-35

28.9 ± 7.1

31.7 ± 8.4

34.5 ± 8.9

>65

30.1 ± 9.1

27.7 ± 8.3

31.9 ± 9.7

25-35

32.3 ± 9.7

30.6 ± 6.6

36.3 ± 8.8

BMI (wt/ht2), mean

Serum 25OHD (ng/ml), mean

Serum 1.25(OH)2D pg/ml), mean

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20 mg (% AD/L, BMI corrected), mean

100 mg (% AD/L, BMI corrected), mean

Ca INTAKE (mg/day), mean

Vitamin D intake (IU/day), mean

>65

33.5 ± 6.1

35.0 ± 5.5

31.8 ± 8.8

25-35

0.16 ± 0.04

0.148 ± 0.06

0.15 ± 0.04

>65

0.12 ± 0.04

0.12 ± 0.03

0.12 ± 0.04

25-35

0.12 ± 0.04

0.13 ± 0.04

0.12 ± 0.04

>65

0.08 ± 0.01

0.09 ± 0.03

0.09 ± 0.01

25-35

770 ± 183

725 ± 324

829 ± 302

>65

737 ± 370

670 ± 287

637 ± 179

25-35

116 ± 55

127 ± 84

150 ± 101

>65

130 ± 63

148 ± 101

157 ± 78

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Fig. 1. Effect of VDR genotypes on calcium absorption. (Upper) 20 mg carrier; (Lower) 100 mg carrier. Next figure: Figure 2

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa

Figure 2 (For magnified figure, select here)

Fig. 2. Effect of VDR genotype on VDR protein concentration.

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Calcified Tissue International 60, 491 (1997)

Calcif Tissue Int 60, 491 (1997) © Springer-Verlag New York, Inc. 1997

Effect of Vitamin D Receptor Genotypes on Calcium Absorption, Duodenal Vitamin D Receptor Concentration, and Serum 1,25 Dihydroxyvitamin D Levels in Normal Women H. K. Kinyamu, J. C. Gallagher, J. A. Knezetic, H. F. DeLuca, J. M. Prahl, S. J. Lanspa

Figure 3 (For magnified figure, select here)

Fig. 3. Effect of VDR genotype on serum 1,25 dihydroxyvitamin D.

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