Genetic Influences on Bone Density: Physiological Correlates of Vitamin D Receptor Gene Alleles in Premenopausal Women. Notification of Genotype Corrections

Gabrielle Howard, Tuan Nguyen and Nigel Morrison

Takako Watanabe, Philip Sambrook, John Eisman, and Paul Kelly The Garvan Institute of Medical Research Sydney, New South Wales 2010, Australia

It has come to our attention that there were some errors in the genotyping used in our study of the genetic influences on bone density (1). The subjects were drawn in part from a larger study (Nature: 1994: 367: 284–287. Prediction of Bone Density by VDR Alleles) in which errors have been reported. We would like to notify the scientific community of these changes and of the following findings with the corrected genotyping.

Recently we have noted some errors in vitamin D receptor genotyping, which affected the assignment of the individuals studied. Thus genotyping was repeated by two independent technicians in a blinded fashion, and additional healthy premenopausal subjects were recruited to increase the sample size to 12 in the BB genotype and 16 in the bb genotype. Our original findings of differences in osteocalcin and 1,25-dihydroxyvitamin D between genotypes were not confirmed in this reanalysis. However, as outlined below, iPTH levels were higher and basal urinary calcium excretion greater in the BB genotype, as was the rate and extent of PTH suppression with calcitriol treatment. This was contrary to the original report of a greater PTH response in the bb genotype. Also urinary excretion of calcium and hydroxyproline rose significantly in response to 1,25-dihydroxyvitamin D, but only in the BB homozygotes.

At baseline there were no significant differences between the two genotypes with regard to height, weight, age, bone density, or in osteocalcin or 1,25-dihydroxyvitamin D levels. Subjects in the BB genotype had significantly higher intact parathyroid hormone (iPTH) levels (3.3 ± 0.4 vs. 2.3 ± 0.3 pmol/L, mean ± SEM, P = 0.03), with a trend for lower urinary calcium excretion (0.22 ± 0.07 vs. 0.39 ± 0.06 mmol/mmol, P = 0.08). Serum 1,25-dihydroxyvitamin D rose to a similar extent in both genotypes after calcitriol stimulation, and serum ionized calcium, phosphate and TmPO4 also responded similarly in both genotypes. The decrease in iPTH was greater in the BB genotype (-1.3 ± 0.2 vs. -0.45 ± 0.2 pmol/L, BB vs. bb, P = 0.04) and occurred earlier (day 2 vs. day 4). Serum osteocalcin levels increased in both genotypes, but the apparently greater rise by day 2 in bb vs. BB individuals did not achieve significance (3.6 ± 0.6 µg/L vs. 1.8 ± 0.9 mg/L, P = 0.1). An increase in urinary calcium/creatinine (Ca/Crt) and hydroxyproline excretion in response to 1,25-dihydroxyvitamin D was apparent only in the BB genotype; differences were (BB, 0.08 ± 0.04 mmol/mmol, P = 0.0001, vs. bb, 0.02 ± 0.04 mmol/mmol, P = 0.07) and (BB, 2 ± 2, P = 0.04, vs. bb, 1 ± 1 µmol/mmol, P = 0.2), respectively.

Thus after correction of genotyping errors and increasing the sample size, a VDR genotype related difference in both basal calcium homeostasis and response to calcitriol stimulation was still observed in healthy premenopausal women. Although basal differences in 1,25-dihydroxyvitamin D levels were not detected between VDR homozygotes in the present study, studies with larger sample sizes have reported higher 1,25-dihydroxyvitamin D and osteocalcin levels in the BB allele (2). Higher levels of iPTH in the BB genotype have also recently been reported in hyperparathyroid patients (3). Overall these reanalyzed data are consistent with a difference in response to calcitriol according to VDR genotype.

Footnotes

Address correspondence to: Dr. Gabrielle Howard, The Garvan Institute of Medical Research, St. Vincent’s Hospital, 384 Victoria Street, Darlinghurst, Sydney, NSW 2010, Australia.

Received December 8, 1997.

References

  1. Howard G, Nguyen T, Morrison N, et al. 1995 Genetic influences on bone density: physiological correlates of vitamin D receptor gene alleles in premenopausal women. J Clin Endocrinol Metab. 80:2800–2805.[Abstract]
  2. Tokita A, Matsumoto H, Morrison N, et al. 1996 Vitamin D receptor alleles, bone mineral density and turnover in premenopausal Japanese women. J Bone Miner Res. 11:1003–1009.[Medline]
  3. Carling T, Kindmark A, Hellman P, et al. 1995 Vitamin D receptor genotypes in primary hyperparathyroidism. Nature Med. 1:1309–1311.[Medline]