Bone density achieved in early adulthood is the major determinant of risk of osteoporotic fracture. Up to 60% of women suffer osteoporotic fractures as a result of low bone density, which is under strong genetic control acting through effects on bone turnover. Here we show that common allelic variants in the gene encoding the vitamin D receptor can be used to predict differences in bone density, accounting for up to 75% of the total genetic effect on bone density in healthy individuals. The genotype associated with lower bone density was overrepresented in postmenopausal women with bone densities more than 2 standard deviations below values in young normal women. The molecular mechanisms by which bone density is regulated by the vitamin D receptor gene are not certain, although allelic differences in the 3' untranslated region may alter messenger RNA levels. These findings could open new avenues to the development and targeting of prophylactic interventions. It follows that other pathophysiological processes considered to be subject to complex multifactorial genetic regulation may also be modulated by a single gene with pleiotropic transcriptional actions.

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We identified a human multiprotein complex (WINAC) that directly interacts with the vitamin D receptor (VDR) through the Williams syndrome transcription factor (WSTF). WINAC has ATP-dependent chromatin-remodeling activity and contains both SWI/SNF components and DNA replication-related factors. The latter might explain a WINAC requirement for normal S phase progression. WINAC mediates the recruitment of unliganded VDR to VDR target sites in promoters, while subsequent binding of coregulators requires ligand binding. This recruitment order exemplifies that an interaction of a sequence-specific regulator with a chromatin-remodeling complex can organize nucleosomal arrays at specific local sites in order to make promoters accessible for coregulators. Furthermore, overexpression of WSTF could restore the impaired recruitment of VDR to vitamin D regulated promoters in fibroblasts from Williams syndrome patients. This suggests that WINAC dysfunction contributes to Williams syndrome, which could therefore be considered, at least in part, a chromatin-remodeling factor disease.

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Although some studies have reported a relationship between several candidate polymorphic genes and bone mineral density (BMD), little is known concerning the genetic factors influencing BMD in children. This study examined this relationship in healthy Japanese girls (n=125; age, 13.4 +/- 0.89 years; range, 12-15 years). We investigated allelic variants of the vitamin D receptor (VDR) gene, the estrogen receptor (ER) gene, the parathyroid hormone (PTH) gene, the Ca-sensing receptor (CaSR) gene, and the beta3-adrenergic receptor (beta3-AR) gene. The genotype of the VDR gene (Fok I) correlated with lumbar spine, and femoral neck BMD. The PTH polymorphisms (BstB I, Dra II) were also associated with lumbar spine BMD. No relationship was found between genotypes of the ER gene, CaSR gene, or beta3-AR gene and BMD. The age, height, weight, and body mass index did not differ significantly among girls with different VDR and PTH genotypes. These results suggest that the Fok I polymorphism of the VDR gene and the Dra II polymorphism of the PTH gene are risk factors for low bone density in Japanese girls.

Recent studies have shown that genetic effects on bone mineral density (BMD) and bone turnover are related to allelic variation in the vitamin D receptor (VDR) gene. We examined allelic influences of the VDR gene on bone turnover and density in 202 normal healthy premenopausal Japanese women (age 30.1 +/- 1.2, mean +/- SEM). The VDR effect on BMD and turnover is similar to that observed in Caucasian women; however, there are major differences in allele frequency. The B allele by BsmI restriction fragment length polymorphisms (RFLPs), associated with low BMD and high bone turnover, is found in only 12% of Japanese women (1.4% homozygote BB), compared with 41% of Caucasians (16.7% homozygote BB). In comparing the two most frequent genotypes, Bb heterozygotes (21.5%) and bb homozygotes (77.1%), BMD is 5.3% lower in Bb heterozygotes, and levels of bone formation markers including osteocalcin and bone-specific alkaline phosphatase are 20-32% higher with lower serum calcium (2.30 +/- 0.02 vs 2.35 +/- 0.01 mmol/l) and higher 1,25-dihydroxyvitamin D (95 +/- 4.8 vs. 76 +/- 3.8 pmol/l). Further discrimination of the genotype was achieved using two additional RFLPs (ApaI, A and TaqI, T); the lumbar spine BMD of the common genotype BbAATt was 9.3% (0.94 SD) lower than in the bbaaTT genotype in premenopausal Japanese women. These data confirm that VDR RFLPs affect bone mineral metabolism regardless of racial differences. Moreover, the VDR genotypes based on haplotype analysis should yield useful insights into the potential prevention of osteoporosis.