Vitamin D receptor gene start codon polymorphisms (FokI) and bone mineral density: interaction with age, dietary calcium, and 3'-end region polymorphisms

Genetics of hypercalciuria and calcium nephrolithiasis: from the rare monogenic to the common polygenic forms

Idiopathic calcium nephrolithiasis is a multifactorial disease with a pathogenesis that involves a complex interaction of environmental and individual factors. This review discusses what is known about monogenic renal calcium stone-related disorders, provides an update on genetic research in calcium nephrolithiasis and such intermediate phenotypes as idiopathic hypercalciuria, discusses the problems that these conditions pose to clinicians and geneticists interested in their pathogenesis, and proposes some method tools potentially useful in this research frame of reference.

Vitamin D Receptor Gene Polymorphisms and Breast Cancer Risk

PURPOSE

The steroid hormone 1,25-dihydroxyvitamin D3 is thought to protect against breast cancer. The actions of 1,25-dihydroxyvitamin D3 are mediated via the vitamin D receptor (VDR), and a number of polymorphisms in the VDR gene have been identified. These result in distinct genotypes, some of which may alter susceptibility to breast cancer. We have investigated whether specific VDR gene polymorphisms are associated with breast cancer risk in a United Kingdom Caucasian population.

EXPERIMENTAL DESIGN

In a retrospective case-control study, female breast cancer patients (n = 398) and control women (n = 427) were recruited, and three VDR polymorphisms were determined.

RESULTS

The 3' VDR polymorphisms BsmI and variable-length poly(adenylate) sequence were both significantly associated with breast cancer risk; odds ratios (adjusted for age menopausal status and hormone replacement therapy usage) for bb genotype versus BB genotype = 1.92 (95% confidence interval, 1.20-3.10; P < 0.01) and for LL versus SS = 1.94 (95% confidence interval, 1.20-3.14; P < 0.01). A 5' VDR gene variant, FokI, was not associated with breast cancer risk when analyzed in isolation (P > 0.05). However, FokI did modulate the increased risk associated with the bb/LL genotype such that possession of one or more F alleles together with the bb/LL genotype augmented breast cancer risk. Furthermore, the highest proportion of bb and FFLL/FfLL genotypes occurred in women with metastatic breast cancer.

CONCLUSIONS

VDR polymorphisms are associated with breast cancer risk and may be associated with disease progression. Additional investigations into how different genotypes may affect the functional mechanisms of the VDR will provide a better strategy for identifying women at risk of breast cancer and for developing improved treatments.

Polymorphisms in the low-density lipoprotein receptor-related protein 5 (LRP5) gene are associated with variation in vertebral bone mass, vertebral bone size, and stature in whites

Stature, bone size, and bone mass are interrelated traits with high heritability, but the major genes that govern these phenotypes remain unknown. Independent genomewide quantitative-trait locus studies have suggested a locus for bone-mineral density and stature at chromosome 11q12-13, a region harboring the low-density lipoprotein receptor-related protein 5 (LRP5) gene. Mutations in the LRP5 gene were recently implicated in osteoporosis-pseudoglioma and "high-bone-mass" syndromes. To test whether polymorphisms in the LRP5 gene contribute to bone-mass determination in the general population, we studied a cross-sectional cohort of 889 healthy whites of both sexes. Significant associations were found for a missense substitution in exon 9 (c.2047G-->A) with lumbar spine (LS)-bone-mineral content (BMC) (P=.0032), with bone area (P=.0014), and with stature (P=.0062). The associations were observed mainly in adult men, in whom LRP5 polymorphisms accounted for <or=15% of the traits' variances. Results of haplotype analysis of five single-nucleotide polymorphisms in the LRP5 region suggest that additional genetic variation within the locus might also contribute to bone-mass and size determination. To confirm our results, we investigated whether LRP5 haplotypes were associated with 1-year gain in vertebral bone mass and size in 386 prepubertal children. Significant associations were observed for changes in BMC (P=.0348) and bone area (P=.0286) in males but not females, independently supporting our observations of a mostly male-specific effect, as seen in the adults. Together, these results suggest that LRP5 variants significantly contribute to LS-bone-mass and size determination in men by influencing vertebral bone growth during childhood.

Association between AIDS disease progression rates and the Fok-I polymorphism of the VDR gene in a cohort of HIV-1 seropositive patients

In addition to its role in mineral metabolism, 1,25-dihydroxivitamin D3 (1,25(OH)2D3) also has immunomodulatory effects. Vitamin D receptor (VDR) mediates genomic actions of 1,25(OH)2D3, by acting as a transcription factor that modulates the expression of several 1,25(OH)2D3 response genes. Variations at the VDR locus have been associated with susceptibility and progression to several immune diseases. We investigated the association between rates of progression to acquired immunodeficiency syndrome (AIDS) and the Fok-I polymorphism, which is located at the initiation codon of the VDR gene. The study was performed with a cohort of 185 patients infected with human immunodeficiency virus type 1 (HIV-1): all belonged to the intravenous drug abuse risk group. Progression to AIDS was according to the Centers for Disease Control 1993 criterion (CDC-1993). In addition, a first drop in CD4 cell count to below 200 microL(-1) was considered as outcome. Patients who reached outcomes during follow-up were considered progressors. Non-progressors were those patients remaining outcome-free after a minimum follow-up of 8 years. Heterozygous at the Fok-I polymorphism were over-represented in the group of patients that progressed to AIDS CDC-1993 (50% of progressors versus 36% of non-progressors, P=0.061; risk ratio (RR)=1.38 (95% confidence interval (CI): 0.98-1.96)) and in the group of patients that showed a drop in CD4 cell count to below 200 microL(-1) (52% of progressors versus 36% of non-progressors, P=0.037; RR=1.44 (95% CI: 1.02-2.03)). Mean time to AIDS CDC-1993 was shorter for those with Ff genotype than for those with FF and ff genotypes (non-Ff genotype patients), (log rank test P=0.035; Cox hazard ratio (HR) for Ff versus non-Ff=1.53 (95% CI: 1.0-2.33), P=0.047). In addition the drop in CD4 cell count to below 200 microL(-1) was reached faster in Ff carriers than in non-Ff patients (log rank test P=0.015; HR for Ff versus non-Ff=1.77 (95% CI: 1.12-2.8), P=0.014). According to these results, HIV-1 seropositive patients carrying the Ff genotype could be considered prone to a faster progression to AIDS.

Vitamin D receptor gene polymorphisms in relation to Vitamin D related disease states

The role in skeletal metabolism of the steroid hormone Vitamin D and its nuclear receptor (VDR) is well known. In addition, however, Vitamin D is also involved in a wide variety of other biological processes including modulation of the immune response and regulation of cell proliferation and differentiation. Variations in the Vitamin D endocrine system have thus been linked to several diseases, including osteoarthritis, diabetes, cancer, cardiovascular disease and tuberculosis. Evidence to support this pleiotropic character of Vitamin D has included epidemiological studies on circulating Vitamin D hormone levels, but also genetic epidemiological studies. Genetic studies provide excellent opportunities to link molecular insights with epidemiological data and have therefore gained much interest. DNA sequence variations which occur frequently in the population are referred to as "polymorphisms" and are usually suspected of having only modest and subtle effects. Recent studies have indicated many polymorphisms to exist in the VDR gene, but the influence of VDR gene polymorphisms on VDR protein function are largely unknown. Sofar, three adjacent restriction fragment length polymorphisms (RFLP) for BsmI, ApaI and TaqI, respectively, at the 3' end of the VDR gene have been the most frequently studied sofar. But because these polymorphisms are probably non-functional, linkage disequilibrium (LD) with one or more truly functional polymorphisms elsewhere in the VDR gene is assumed to explain the associations observed. Research is therefore focussed on documenting additional polymorphisms across the VDR gene to verify this hypothesis, and on trying to understand the functional consequences of the variations. Substantial progress has been made including the discovery of novel polymorphisms in the large promoter region of the VDR gene. Eventually, results of this research will deepen our understanding of variability in the Vitamin D endocrine system and might find applications in risk-assessment of disease and in predicting response-to-treatment.

Association between Vitamin D receptor polymorphisms and the rate of bone loss in elderly women-importance of adjusting for dietary and lifestyle factors

The association between the restriction length polymorphisms of the Vitamin D receptor (VDR) gene and the bone mineral density (BMD) or the rate of bone loss is still under debate. In a longitudinal study of untreated postmenopausal elderly women, we evaluated the relationship between the VDR gene polymorphisms (BsmI, TaqI, ApaI, and FokI) and the rate of bone loss over a 3-year period. We also examined the effect of adjustments for dietary and lifestyle factors on these associations. Before adjustments, the rate of femoral neck bone loss was - 3.76 +/- 1.58% in women with BB genotype and 0.45 +/- 0.65% in women with bb genotype, which was not significantly different. Upon adjustment for dietary and lifestyle factors, statistically significant (P = 0.03) bone loss was observed at femoral neck in women with BB genotype (- 3.66 +/- 2.44%) compared to that of bb genotype (2.39 +/- 1.32%). Similar results were observed with TaqI genotypes. The rates of bone loss at other skeletal sites were not different between VDR genotypes defined by BsmI and TaqI. VDR gene polymorphisms defined by ApaI and FokI were not related to the rate of bone loss.

Association of bone mineral density with vitamin D and estrogen receptor gene polymorphisms during GnRH agonist treatment

AIMS

This study examined whether or not a decrease in bone mineral density (BMD) induced by the use of gonadotropin-releasing hormone agonist (GnRHa) during sexual maturation is affected by vitamin D receptor and/or estrogen receptor gene polymorphisms, like the phenomenon observed during the postmenopausal period.

METHODS

In 43 patients who received GnRHa therapy for 6 months to treat uterine myoma or endometriosis at our department and who were confirmed to have pituitary down-regulation, we measured bone density before and after GnRHa treatment using DXA and analyzed the bone metabolism turnover using bone metabolic markers. Polymorphisms were analyzed by RFLP using FokI and TaqI for the vitamin D receptor gene and PvuII and XbaI for the estrogen receptor gene. The then determined gene polymorphism was analyzed in relation to the percentage decreases in BMD following GnRHa treatment.

RESULTS

The patients were divided by f, t into two groups: (f, t) < 2 (Group V-I) and (f, t) > or = 2 (Group V-II). They were also divided by P, x into two groups (P, x) < 3 (Group E-I) and (P, x) > or = 3 (Group E-II). The BMD change was significantly higher in Group V-II than in Group V-I. Group E-II tended to have a higher BMD change than Group E-I, although this difference was not statistically significant.

CONCLUSION

Patients who often have f and t polymorphism are more likely to show BMD reduction following GnRHa therapy, like the phenomenon seen during the postmenopausal period, than patients with other gene polymorphisms. Measures to avoid BMD reduction are required when using GnRHa in such patients.

Vitamin D receptor initiation codon polymorphism, bone density and inflammatory activity of patients with ankylosing spondylitis

OBJECTIVES

Osteoporosis is a common finding in ankylosing spondylitis (AS) and may contribute to spinal deformity and bone pain. Bone metabolism as well as inflammatory processes are influenced by the vitamin D receptor gene (VDR). We investigated initiation codon ( FokI) and 3'UTR ( BsmI) polymorphisms of the VDR for whether there could be an association with bone mineral density (BMD) in relation to bone metabolism or inflammatory activity in patients with AS.

METHODS

In this study, 104 patients with AS (m/w 71/33, mean age 41+/-12 years) were investigated for their lumbar and femoral BMD by DEXA and in part by QCT measurements and compared to 54 healthy controls. Disease activity indices, serum markers of bone metabolism and inflammation were recorded. FokI and BsmI polymorphisms of the VDR were genotyped using genomic DNA from peripheral leukocytes with present or absent restriction sites defined as alleles " f" and " b" or " F" and " B," respectively.

RESULTS

In male AS patients, FokI genotypes were significantly associated with spinal but not with femoral BMD values ( P=0.01) as independent predictors of low BMD, which was also influenced by BMI, and inflammatory and pain indices. CRP and ESR values were also significantly associated with FokI genotypes. BMD in female patients showed no significant association with either FokI or BsmI genotypes of the VDR.

CONCLUSION

This is the first evidence that the VDR gene may be involved in BMD differences, bone metabolism and inflammatory processes in ankylosing spondylitis. A possible interaction of the vitamin D system, cytokines and bone could define new diagnostic and therapeutic implications in ankylosing spondylitis.

Associations of polymorphisms in the vitamin D receptor gene (BsmI and FokI) with bone mineral density in postmenopausal women in Malta

Previous studies have suggested that variations in the vitamin D receptor (VDR) gene are related to bone mineral density (BMD). In this study, the T-->C transition in the start codon and the G-->A polymorphism at the 3' end of the VDR gene, identified by endonucleases FokI and BsmI, respectively, were analysed and correlated with BMD in postmenopausal Maltese women ( n=104). Genotype frequencies observed for the VDR start codon polymorphism (SCP) were CC: 60.4%; CT: 30.7% and TT: 8.9%, while those observed for the 3' in this study were GG: 16.4%; GA: 51.9%; AA: 31.7%. In postmenopausal women, both lumbar and femoral BMD were observed to be highest in CC homozygotes for the FokI genotype and in GG homozygotes for the BsmI genotype, although in both groups the difference between the genotypes was not statistically significant, even after adjusting BMD for age, BMI and years since menopause. No evidence of linkage disequilibrium between the two alleles was observed.

Establishment of peak bone mass

Among the main areas of progress in osteoporosis research during the last decade or so are the general recognition that this condition, which is the cause of so much pain in the elderly population, has its antecedents in childhood and the identification of the structural basis accounting for much of the differences in bone strength among humans. Nevertheless, current understanding of the bone mineral accrual process is far from complete. The search for genes that regulate bone mass acquisition is ongoing, and current results are not sufficient to identify subjects at risk. However, there is solid evidence that BMD measurements can be helpful for the selection of subjects that presumably would benefit from preventive interventions. The questions regarding the type of preventive interventions, their magnitude, and duration remain unanswered. Carefully designed controlled trials are needed. Nevertheless, previous experience indicates that weight-bearing activity and possibly calcium supplements are beneficial if they are begun during childhood and preferably before the onset of puberty. Modification of unhealthy lifestyles and increments in exercise or calcium assumption are logical interventions that should be implemented to improve bone mass gains in all children and adolescents who are at risk of failing to achieve an optimal peak bone mass.

The role of vitamin D receptor gene polymorphisms in bone biology

The role of vitamin D and its receptor (VDR) in skeletal metabolism is well known but the vitamin D endocrine system seems to play an important role in other metabolic pathways as well, such as those involved in osteoarthritis, the immune response and cancer. One approach to understand the vitamin D endocrine system is to study the influence of variations in the DNA sequence of important proteins of this system. For example, deleterious mutations in the VDR gene cause 1,25-dihydroxyvitamin D-resistant rickets, a rare monogenetic disease. More subtle sequence variations (polymorphisms) in the VDR gene occur much more frequently but their effects are poorly understood. Their influence on the vitamin D endocrine system is currently under scrutiny in relation to a number of so-called complex diseases and traits such as osteoporosis. The interpretation of polymorphic variations in the VDR gene is severely hindered by the fact that several of the polymorphisms used have unknown effects. However, current data indicate that dozens of additional polymorphic variations exist in the VDR gene that could each have different types of consequences. Therefore, efforts are focussed on finding novel sequence variations and to study their interaction in molecular- and cell-biological experiments as well as in genomic epidemiological studies. The ultimate goal of this approach is to identify the combinations of functional sequence variants that modulate the vitamin D endocrine system and confer risk of disease.

Vitamin D receptor gene allelic variants, bone density, and bone turnover in community-dwelling men

The role of vitamin D receptor (VDR) gene polymorphisms in the determination of bone mass and bone turnover is controversial in women. The aim of the study was to determine whether VDR polymorphisms are associated with indices of bone mineral density (BMD) (by dual-energy X-ray absorptiometry and by ultrasound) and/or with bone turnover and muscle strength, factors related to both BMD and fracture risk. For this purpose, we investigated a cohort of community-dwelling men >70 years (n = 271) and a group of healthy control subjects between the ages of 20 and 50 years (n = 137). VDR TaqI, ApaI, and FokI genotypes were determined using enzymatic restriction digestion of polymerase chain reaction (PCR) fragments. In the elderly group, the lowest BMD value at the femoral neck and at the calcaneus was observed in subjects with the "At-At" haplotype genotype, with differences between extreme haplotype groups ("At-At" vs. noncarriers of the "At" allele) ranging from 5.8% to 34.3% (p < or = 0.05). Moreover, at the different subregions of the distal forearm and the tibia, the lowest BMD estimates were consistently associated in both elderly and younger men with the "At" haplotype allele, although this did not approach statistical significance. Elderly subjects with the "At-At" genotype had a significantly higher serum osteocalcin level. BMD was not significantly related to the FokI VDR polymorphism at any of the assessed skeletal sites, nor were any of the biochemical markers associated with the FokI VDR genotype. There were no differences between genotype groups for any of the indices of muscle strength. The present study indicates that the VDR genotype is associated with BMD in healthy community-dwelling elderly men and tends to be associated with biochemical markers, particularly of bone formation, in elderly men.

Lack of association between the SOST gene and bone mineral density in perimenopausal women: analysis of five polymorphisms

Osteoporosis is a common disease characterized by a decrease in bone mass, architectural deterioration of the bone tissue, and an increased risk of fracture. The condition is under strong genetic control, involving a large variety of gene products, but to date the genes responsible remain poorly defined. Although population-based studies have identified polymorphisms in several candidate genes that are associated with bone mineral density (BMD), these account for only a small proportion of the population variance in bone mass. In this study, we looked for evidence of an allelic association between polymorphisms in the SOST gene and BMD. This gene was analyzed because loss-of-function mutations in SOST cause sclerosteosis, a sclerosing bone dysplasia associated with increased bone mass due to increased bone formation. We identified 26 different polymorphisms in the SOST gene and selected 5 of these for association analysis in a case-control study of 619 women with either high or low BMD, drawn from a random population-based survey of 5119 perimenopausal white women. The high BMD group comprised 326 women in whom lumbar spine BMD values adjusted for age, height, and weight were in the highest 16% of the population distribution, and the low BMD group comprised 293 women in whom BMD values were in the lowest 16% of the population distribution. The distribution of genotypes and alleles for each Single Nucleotide Polymorphism (SNP) examined did not differ in the low and high BMD groups. We conclude that, in this population, common allelic variations in the SOST gene do not contribute significantly to the regulation of high or low BMD.

Strategies for skeletal health in the elderly

Osteoporosis is a common disease in the elderly, and the fractures that result from this disorder affect 40 % of women and 14 % of men over the age of 50 years. The risk of fracture relates to bone mineral density and the risk of falling, among other factors. Low bone mineral density in the elderly can result from either low peak bone mass or accelerated bone loss, or a combination of the two. Nutritional factors play a role in both the attainment of peak bone mass and in the rate of age-related bone loss. The main determinants of peak bone mass are genetic factors, early-life nutrition, diet and exercise. Of the nutritional factors Ca, and particularly milk, are the most important contributors to peak bone mass. Some of these factors may interact; for example, a low dietary Ca in addition to an unfavourable vitamin D receptor gene polymorphism may result in low peak bone mass. The age-related changes in bone mass may also have a genetic basis, but deficiency of oestrogen is a major contributor. In addition, undernutrition is common in the elderly, and lack of dietary protein contributes both to impaired bone mineral conservation and increased propensity to fall. There is a decreased ability of the intestine to adapt to a low-Ca diet with increasing age. Other dietary factors include vitamin K, Zn and fruit and vegetables. Adequate nutritional status, particularly of Ca and vitamin D, is essential for the successful pharmaceutical treatment of osteoporosis. Thus, strategies for enhancing skeletal health in the elderly must begin in early childhood, and continue throughout life.

Genetics of osteoporosis: role of steroid hormone receptor gene polymorphisms

Osteoporosis is a common skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture. In the past years, twin and family study have shown that this disease recognizes a strong genetic component and that genetic factors play an important role in regulating bone mineral density (BMD). While in few isolate conditions osteoporosis can be inherited in a simple Mendelian pattern, due to single gene mutations, in the majority of cases has to be considered a multifactorial polygenic disease in which genetic determinants are modulated by hormonal, environmental and nutritional factors. Given the important role that steroid hormones play in bone cell development and in the maintenance of normal bone architecture, polymorphisms at receptor of the steroid/thyroid hormone receptor superfamily, such as estrogen receptor alpha (ERalpha) and Vitamin D receptor (VDR) have been thoroughly investigated in the last years and appeared to represent important candidate genes. The individual contribution of these genetic polymorphisms to the pathogenesis of osteoporosis remains to be universally confirmed and an important aim in future work will be to define their functional molecular consequences and how these polymorphisms interact with each other and with the environment to cause the osteoporotic phenotype. A further promising application of genetic studies in osteoporosis comes from their pharmacogenomic implications, with the possibility to give a better guidance for therapeutic agents commonly used to treat this invalidating disorder or to identify target molecules for new therapeutic agents.

Fatores de risco da osteoporose: prevenção e detecção através do monitoramento clínico e genético

A osteoporose é uma doença sistêmica caracterizada pela baixa massa óssea e deterioração da micro arquitetura do tecido ósseo. Consequentemente existe um aumento na fragilidade do osso e suscetibilidade à fratura, que é considerada o efeito clínico mais importante deste processo. Muitos estudos que se utilizam de modelos em gêmeos ou pais e seus descendentes têm confirmado o papel da herança genética no pico de massa óssea, na verdade o maior fator de risco da fratura. Neste artigo de revisão, são enfocados os prováveis genes envolvidos no processo de osteoporose, ressaltando a importância das interações entre gene- gene e gene-ambiente. Concernente à influência isolada do ambiente, são abordados os hábitos relacionados ao estilo de vida, à nutrição e ao tabagismo envolvidos no aparecimento dessa doença. Durante os próximos anos, o conhecimento baseado na genética molecular elucidará o processo osteoporótico. Do mesmo modo, os estudos clínicos se expandirão, visando contribuir para a detecção precoce da doença, permitindo assim a aplicação de medidas preventivas e terapêuticas adequadas.

Polymorphism in the type I collagen (COLIA1) gene and risk of fractures in postmenopausal women

Twin and family studies have demonstrated that a large part of a population's variance in bone mineral density (BMD) is attributable to genetic factors. A polymorphism in the collagen type I alpha1 (COLIA1) gene has recently been associated with low bone mass and fracture incidence. We analyzed the relationship between COLIA1 gene polymorphism, lumbar spine and hip BMD, and fracture prevalence in a population of 319 postmenopausal women classified by WHO standards, including 98 nonosteoporotic women (NOPW) and 221 osteoporotic postmenopausal women (OPW), divided into 139 osteoporotic women without fracture (OPWnF) and 82 osteoporotic women with fracture (OPWwF). The COLIA1 genotype was assessed by polymerase chain reaction and BalI endonuclease digestion. Genotype frequencies for the total group were 49.2% GG homozygotes, 39.5% GT heterozygotes, and 11.3% TT homozygotes. We found significant differences in the percentage of homozygous TT between NOPW and OPW (6.1% and 13.6%, respectively). Significantly, the occurrence of genotype TT in OPWnF was 6.2%, and 28% in OPWwF. We observed no associations between the COLIA1 genotype and lumbar spine and hip BMD. The prevalence of fractures varied significantly by genotype: GG, 26.1%; GT, 15.9%; and TT, 58.3%. Logistic regression analysis of fracture prevalence showed that, for prevalent fractures, the women with the TT genotype had a 5.9-fold increased risk when compared with the other genotypes (GG + GT). When prevalence was adjusted for age, body mass index, and BMD, the fracture risk was 4.8 for the TT group vs. the genotype GG, whereas it was 0.6 for the GT genotype. In conclusion, we found the COLIA1 Sp1 TT genotype to be associated with an increased fracture risk in postmenopausal women. Interestingly, this genotype-dependent risk could not be explained completely by BMD differences.

The genetics of osteoporosis

A genetic component clearly contributes to bone mass determination by influencing peak bone mass acquisition or, to a lesser degree, bone loss later in life. The analysis of genetic markers for osteoporosis is complex because multiple genes are involved and because osteoporosis is a multifactorial disease. The influence of a number of candidate gene alleles on bone mass has been studied in various populations. Results have been inconsistent and, at times, contradictory, as illustrated by studies on the vitamin D receptor gene. The most conclusive finding is the association linking the Sp1 polymorphism of type I collagen to bone mineral density and osteoporotic fractures. Polymorphisms of other genes either have very little influence or remain unexplored. In all likelihood, the best predictive value will be obtained by using a combination of several gene polymorphisms.

Genetics of menopause-associated diseases

Menopause is the permanent cessation of menstruation resulting from the loss of ovarian follicular activity. It is estimated that perhaps 50 million women worldwide will go into menopause annually. Atherosclerotic cardiovascular disease, osteoporotic fractures and Alzheimer's dementia are common chronic disorders after menopause, representing major health problems in most developed countries. Apart from being influenced by environmental factors, these chronic disorders recognize a strong genetic component, and there are now considerable clinic evidences that these disorders are related to low hormonal milieu of postmenopausal women. Here, we review up-to-date available data suggesting that genetic variation may contribute to higher susceptibility to four sporadic chronic syndromes such as osteoporosis (OP), osteoarthritis (OA), Alzheimer's disease (AD) and coronary artery disease (CAD). For these four syndromes candidate genes that today appear as major loci in genetic susceptibility encode for proteins specific of a given system, as the vitamin D receptor (VDR) gene for the skeleton and, therefore, OP or angiotensin converting enzyme (ACE) for the cardiovascular system and, therefore, CAD. The investigation of gene polymorphisms in various pathological conditions typical of postmenopause offer an explanation not only of their genetic inheritance but also of their co-segregation in given individuals. In this view, it may be possible to identify a common set of genes whose variants contribute to a common genetic background for these different disorders. Ideal candidates appear genes of the estrogen response cascade [i.e. estrogen receptor (ERs), enzymes involved in estrogen metabolism or co-activators and co-inhibitors]. All together this information may represent the basis both for future recognition of individuals at risk and for the pharmacogenetic driving of drug responsiveness.

The polymorphism in the caudal-related homeodomain protein Cdx-2 binding element in the human vitamin D receptor gene

The major physiological activity of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is the regulation of calcium absorption in the small intestine, and the level of vitamin D receptor (VDR) is an important factor in this regulation. In a previous study, we indicated-that the caudal-related homeodomain Cdx-2 played an important role in the intestine-specific transcription of the human VDR gene. In this study, the polymorphism was identified in the core sequence 5'-ATAAAAACTTAT-3' in the Cdx-2 binding site in the VDR gene promoter. In 261 Japanese women with genotyped VDR polymorphisms, 48 were genotype Cdx-A (adenine at -3731 nucleotides [nt] relative to the transcription start site of human VDR gene 5-ATAAAAACTTAT), 82 were genotype Cdx-G (guanine at -3731 nt, 5'-GTAAAAACTTAT-3'), and 131 were genotype Cdx-A/G (heterozygote). In postmenopausal Japanese women, the bone mineral density (BMD) in the lumbar spine (L2-L4) with the Cdx-G homozygote was 12% lower than that with the Cdx-A homozygote (p < 0.05). In electrophoretic gel mobility shift assay (EMSA), the oligonucleotide with Cdx-G allele markedly decreased the binding to Cdx-2 compared with that in the Cdx-A allele. The transcriptional activity of the VDR promoter with Cdx-G allele was decreased to 70% of the Cdx-A allele. In addition, in the herpes simplex virus thymidine kinase promoter, the Cdx-2 binding element with the G allele showed significantly lower transcriptional activity than that of the A allele. Thus, the polymorphism in the Cdx-2 binding site of the VDR gene (Cdx-polymorphism) would affect the expression of VDR in the small intestine. In addition, this polymorphism may modulate BMD in postmenopausal Japanese women.

Vitamin D receptor gene polymorphisms are associated with breast cancer risk in a UK Caucasian population

There is increasing evidence that vitamin D can protect against breast cancer. The actions of vitamin D are mediated via the vitamin D receptor (VDR). We have investigated whether polymorphisms in the VDR gene are associated with altered breast cancer risk in a UK Caucasian population. We recruited 241 women following a negative screening mammogram and 181 women with known breast cancer. The VDR polymorphism Bsm I, an intronic 3' gene variant, was significantly associated with increased breast cancer risk: odds ratio bb vs BB genotype = 2.32 (95% CI, 1.23-4.39). The Bsm I polymorphism was in linkage disequilibrium with a candidate translational control site, the variable length poly (A) sequence in the 3' untranslated region. Thus, the 'L' poly (A) variant was also associated with a similar breast cancer risk. A 5' VDR gene variant, Fok I, was not associated with breast cancer risk. Further investigations into the mechanisms of interactions of the VDR with other environmental and/or genetic influences to alter breast cancer risk may lead to a new understanding of the role of vitamin D in the control of cellular and developmental pathways.

Vitamin D receptor initiation codon polymorphism influences genetic susceptibility to type 1 diabetes mellitus in the Japanese population

BACKGROUND

Vitamin D has been shown to exert manifold immunomodulatory effects. Type 1 diabetes mellitus (T1DM) is regarded to be immune-mediated and vitamin D prevents the development of diabetes in the NOD mouse. We studied the association between T1DM and the initiation codon polymorphism in exon 2 of the vitamin D receptor gene in a Japanese population. We also investigated associations between the vitamin D receptor polymorphism and GAD65-antibody (Ab) positivity. We carried out polymerase chain reaction-restriction fragment length polymorphism analysis in 110 Japanese T1DM patients and 250 control subjects. GAD65 antibodies were assessed in 78 patients with T1DM.

RESULTS

We found a significantly higher prevalence of the F allele / the FF genotype in the patients compared to the controls (P = 0.0069 and P = 0.014, respectively). Genotype and allele frequencies differed significantly between GAD65-Ab-positive patients and controls (P = 0.017 and P = 0.012, respectively), but neither between GAD65-Ab-negative patients and controls (P = 0.68 and P = 0.66, respectively) nor between GAD65-Ab-positive and -negative patients (P = 0.19 and P = 0.16, respectively).

CONCLUSIONS

Our findings suggest that the vitamin D receptor initiation codon polymorphism influences genetic susceptibility to T1DM among the Japanese. This polymorphism is also associated with GAD65-Ab-positive T1DM, although the absence of a significant difference between GAD65-Ab-negative patients and controls might be simply due to the small sample size of patients tested for GAD65 antibodies.

Functionally relevant polymorphisms in the human nuclear vitamin D receptor gene

The functional significance of two unlinked human vitamin D receptor (hVDR) gene polymorphisms was evaluated in twenty human fibroblast cell lines. Genotypes at both a Fok I restriction site (F/f) in exon II and a singlet (A) repeat in exon IX (L/S) were determined, and relative transcription activities of endogenous hVDR proteins were measured using a transfected, 1,25-dihydroxyvitamin D(3)-responsive reporter gene. Observed activities ranged from 2--100-fold induction by hormone, with higher activity being displayed by the F and the L biallelic forms. Only when genotypes at both sites were considered simultaneously did statistically significant differences emerge. Moreover, the correlation between hVDR activity and genotype segregated further into clearly defined high and low activity groups with similar genotypic distributions. These results not only demonstrate functional relevance for both the F/f and L/S common polymorphisms in hVDR, but also provide novel evidence for a third genetic variable impacting receptor potency.

An assessment of genetic markers as predictors of bone turnover in healthy adults

In 1992 a significant relationship between bone turnover and the vitamin D receptor (VDR) genotype was reported in Australian subjects of UK-Irish decent. Since then, several groups have investigated the relationship between VDR and other bone-related genotypes, bone mass and bone turnover in several populations. However, the results of these studies are conflicting. Therefore, our aim was to determine bone-related genotypes in a population of healthy Irish adults and relate these genotypes to the rate of bone turnover. One hundred and eighteen healthy Irish adults (aged 19-67 yr) were recruited and fasting blood and first void urines were collected from each subject. Bone-related genotype frequencies in healthy Irish adults were similar to those reported in other Caucasian populations and were in Hardy-Weinberg equilibrium. Estrogen receptor (Pvu II or Xba I), apolipoprotein E and collagen IA1 genotypes were not related to bone turnover. The tt VDR genotype was associated with significantly higher serum osteocalcin (29% and 40%) compared with the Tt and TT genotypes, respectively. The ff VDR genotype was associated with significantly higher urinary pyridinoline (by approximately 44% and approximately 29%) and deoxypyridinoline (by approximately 76% and approximately 58%) levels and higher serum osteocalcin (by approximately 25% and approximately 53%) compared with the Ff or FF genotypes, respectively. These findings suggest that healthy Irish adults with either the tt or ff VDR genotype have higher rates of bone turnover than those with Tt or TT, or Ff or FF genotypes, respectively, and therefore may have a higher risk of low bone mineral density and osteoporosis in later life.

Genetic markers of osteoarticular disorders: facts and hopes

Osteoarthritis and osteoporosis are the two most common age-related chronic disorders of articular joints and skeleton, representing a major public health problem in most developed countries. Apart from being influenced by environmental factors, both disorders have a strong genetic component, and there is now considerable evidence from large population studies that these two disorders are inversely related. Thus, an accurate analysis of the genetic component of one of these two multifactorial diseases may provide data of interest for the other. However, the existence of confounding factors must always be borne in mind in interpreting the genetic analysis. In addition, each patient must be given an accurate clinical evaluation, including family history, history of drug treatments, lifestyle, and environment, in order to reduce the background bias. Here, we review the impact of recent work in molecular genetics suggesting that powerful molecular biology techniques will soon make possible both a rapid accumulation of data on the genetics of both disorders and the development of novel diagnostic, prognostic, and therapeutic approaches.

Acquisition of optimal bone mass in childhood and adolescence

Peak bone mass (PBM), which is achieved by early adulthood, is a key determinant of the lifetime risk of osteoporosis. Because the foundation for skeletal health is established so early in life, osteoporosis prevention begins by optimizing gains in bone mineral throughout childhood and adolescence. Heritable factors account for an estimated 60-80% of the variability in PBM, with diet, physical activity and hormonal status serving as important modifiers of bone accrual. Recent pediatric studies have clarified the tempo and magnitude of gains in bone mineral and the modulating effects of diet, activity and sex steroids. The challenge lies in designing effective means to reverse trends of decreased calcium consumption, increased sodium intake and diminished physical activity among children and adolescents. Equally important is raising the awareness of health care providers to recognize children at risk for suboptimal acquisition of PBM.

Vitamin D receptor polymorphisms and nutritional rickets in Nigerian children

Nutritional rickets is common in Nigeria where vitamin D deficiency is rare and dietary insufficiency of calcium is common. It occurs more commonly in siblings of affected children than of unaffected children. Postulating that vitamin D receptor (VDR) polymorphisms might relate to the susceptibility of some Nigerian children to develop rickets in the setting of low calcium intake, we compared the VDR genotypes, as determined by the presence or absence of Bsm I, Apa I, Taq I, and Fok I restriction enzyme cleavage sites, between 105 children with active nutritional rickets and 94 subjects representative of the community from which the rachitic children came. In the rickets group, the ff genotype was less common than in the community group, and the FF genotype was relatively increased (f allele frequency, 17% in rachitic children and 26% in the community group, p = 0.03). Neither individual allele frequencies for the other polymorphisms nor combinations of genotypes at different sites were different between the rachitic and community groups. Although it is not clear why a presumed better-functioning VDR variant (F allele) is associated with an increased risk of developing rickets, this study raises the possibility that VDR alleles might be important in determining an individual's susceptibility to developing rickets when faced with dietary calcium deficiency.

Association of the vitamin D receptor genotype BB with low bone density in hyperthyroidism

Bone mineral density (BMD) is modulated by genetic and environmental factors or certain diseases. In several conditions such as low calcium intake, an influence of vitamin D receptor (VDR) polymorphisms on BMD has been suggested. In the present study, we investigated the relationship of Bsm I and Fok I polymorphisms of the VDR gene and BMD in patients with hyperthyroidism, a disease that often results in low BMD. Bsm I and Fok I genotypes were determined in 76 postmenopausal hyperthyroid patients and 62 healthy postmenopausal women as controls. Patients and controls were matched for age, time since menopause, and lifestyle factors and were free of estrogen medication. BMD evaluation included axial dual X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (PQCT). Low BMD was defined as -2.5 STD below the young adult mean value. Biochemical parameters investigated were thyroid hormones, osteocalcin, and 25-(OH)-vitamin D3 as well as routine laboratory data. Low BMD was found in 61% of hyperthyroid patients and in only 23% of euthyroid controls. In the group of hyperthyroid patients with low bone density, the BB genotype (VDR Bsm I polymorphisms) was significantly more frequent (39%) than in controls (13%; p = 0.003) and hyperthyroid patients with normal BMD (6%; p = 0.013). The odds ratio (OR) for low BMD in patients with BB genotype was 5.7 (95% CI, 1.7-19.1; p < 0.005) as compared with the Bb and bb genotypes and 5.5 (95% CI, 2.3-13.2; p < 0.0001) for hyperthyroidism alone. The cumulative risk for low BMD in patients with hyperthyroidism and BB genotype was 31.4 (95% CI, 3.9-256; p < 0.0003). VDR Fok I genotypes showed no significant relationship with BMD or other general or bone-specific parameters. Thus, hyperthyroidism and the genetic background of a BB genotype may promote synergistically the development of low BMD in hyperthyroid patients. Screening for the BB genotype in these patients therefore could help to identify those with particularly high risk for the development of low BMD and allow early treatment.

Polymorphism in the vitamin D receptor gene and bone mass in African-American and white mothers and children: a preliminary report

OBJECTIVE

To evaluate the contribution of polymorphisms in the vitamin D receptor (VDR) gene to ethnic variations in bone mass in mother and children from different ethnic origins.

METHODS

VDR genotypes and bone mass in 43 African-American and white women, mean age 38.2 years, and 41 of their children were studied. All children had a whole body bone mass measurement at age 9, and 39 had follow up measurements at age 11, while all the mothers had a single measurement. DNA was extracted from peripheral blood samples, subjected to polymerase chain reactions using primers specific for the VDR gene, and the Bsm1 restriction fragment length polymorphism defined.

RESULTS

There was a significant ethnic difference in the VDR genotype frequencies among the adults and the children. No African-American subjects had the genotype "BB". In contrast, there was a 25% frequency of the "BB" genotype in the white adults and 24% in the white children. After pooling the ethnic groups, the mean bone mass in the "bb" genotype was significantly higher than in the "BB" genotype among the mothers, but this was not found in the children at baseline. However, by age 11, those with the "Bb" or "bb" genotypes had a larger gain in bone mass than those with "BB".

CONCLUSION

These data support the suggestion that the ethnic difference in VDR genotype frequencies, together with the association between the genotypes and bone mass, may help to explain the well known ethnic differences in bone mass. Further, our observations suggest that VDR polymorphism may have an effect on bone mass during puberty as peak bone mass is accumulated.

Polymorphisms in the vitamin D receptor gene and bone mass, bone turnover and osteoporotic fractures

BACKGROUND

Vitamin D is essential for normal bone metabolism. Polymorphisms in exon 2, intron 8 and exon 9 of the vitamin D receptor (VDR) gene have previously been found to be associated with bone mass and bone turnover.

MATERIALS AND METHODS

We examined the effect of these polymorphisms, separately and in combination, on bone mineral density (BMD), bone turnover, and the prevalence of osteoporotic fractures in 192 osteoporotic patients and 207 normal controls. The four polymorphisms were determined by RFLP using Fok I (T2-C), Bsm I (intron 8), Apa I (intron 8) and Taq I (T1055-C) after PCR.

RESULTS

We did not find any association between the Fok I polymorphism and bone mass, bone turnover or prevalence of osteoporotic fractures. We found that BB + Bb-genotypes were more frequent in patients with osteoporotic fractures (chi2 = 3.50, P = 0. 06). Furthermore, BMD of the intertrochanteric region (P < 0.0001, ANOVA) as well as the total hip (P < 0.01, ANOVA) were higher in individuals with the bb-genotype. The Apa I and the Taq I polymorphisms were not distributed differently among osteoporotic patients and normal controls. Apa I was not associated with differences in BMD. BMD of the intertrochanteric region was higher in individuals with the TT-genotype compared with individuals with the Tt- or tt-genotypes (P < 0.01, ANOVA), while no differences could be demonstrated in BMD of the lumbar spine, femoral neck, trochanter or Wards triangle. Combining the genotypes generally reflected the differences caused by the Bsm I polymorphism.

CONCLUSION

We have found that the B-allele of the Bsm I polymorphism in the 3' untranslated region of the VDR was associated with low BMD at the hip, and tended to be associated with osteoporotic fractures. The translation initiation polymorphism in the VDR does not affect BMD and is not associated with osteoporotic fractures in men or women.

Vitamin D receptor gene start codon polymorphism (FokI) and bone mineral density in healthy male subjects

OBJECTIVE

The genetic factors determining peak bone mineral density (BMD) in men are not well characterized. Recent studies have investigated the relationship between the start codon polymorphism (SCP) of the vitamin D receptor (VDR) gene and BMD in different populations. We have now examined the relationship between SCP of the VDR gene and BMD in a group of healthy Caucasian men from the north-east of England.

SUBJECTS

Ninety-six healthy men (median age 50, range 40.0-77.0 years).

MEASUREMENTS

Analysis of the FokI genotypes of SCP of the VDR and measurements of BMD at the femoral neck and lumbar spine were performed.

RESULTS

FF, Ff and ff VDR FokI genotypes were found to have the highest, intermediate and the lowest lumbar spine BMD, respectively (Mean +/- SD, for FF 1.07 +/- 0.14, Ff 1.05 +/- 0.16 and ff 0.95 +/- 0.10 g/cm2). There was a significant difference in spine BMD between FF and ff genotypes (P < 0.05, analysis of variance [ANOVA]), but no such difference was apparent between Ff and ff (P > 0.05, ANOVA). Interestingly, there was no association between FokI polymorphism and femoral neck BMD (Mean +/- SD, for FF 0.85 +/- 0.12, Ff 0.87 +/- 0.15 and ff 0.83 +/- 0.15 g/cm2). The distribution of FokI VDR genotypes approached Hardy-Weinberg equilibrium and was similar to that reported for women from different ethnic groups, as the prevalence of FF and ff genotypes was 44% and 16%, respectively.

CONCLUSION

The study shows that in this population of healthy men there is a weak association between lumbar spine bone mineral density and FokI restriction fragment length polymorphism at the translation initiation site of the vitamin D receptor gene.

Association of a polymorphism in the TNFR2 gene with low bone mineral density

Previous genetic linkage data suggested that a gene on chromosome 1p36.2-36.3 might be linked to low bone mineral density (BMD). Here, we examine the gene for tumor necrosis factor receptor 2 (TNFR2), a candidate gene within that interval, for association with low BMD in a group of 159 unrelated individuals. We assess two polymorphic sites within the gene, a microsatellite repeat within intron 4, and a three-nucleotide variation in the 3' untranslated region (UTR) of the gene. The latter has five alleles of which the rarest allele is associated with low spinal BMD Z score (p = 0.008). Lowest mean spinal BMD Z scores were observed for individuals having genotypes that were heterozygous for the rarest allele. No homozygotes for the rarest allele were observed. Preliminary analysis suggests that there is a difference in the genotype frequency distribution between the group with low BMD and a control group.

Vitamin D receptor initiation codon polymorphism in Japanese patients with Graves' disease

Recent studies have shown that related genetic influences on bone mineral density (BMD) and bone turnover are related to allelic variations in the vitamin D receptor (VDR) gene. Osteoporosis as a complication of hyperthyroidism is characterized by increased rates of both bone formation and bone resorption. In addition, VDR gene polymorphism influences susceptibility to some autoimmune diseases such as insulin-dependent diabetes mellitus (IDDM) and multiple sclerosis (MS). In the gene encoding the VDR, we investigated the distribution of a VDR-FokI polymorphism that changes the predicted protein sequence. The subjects were 131 female Japanese patients with Graves' disease and 150 female controls. The distribution of genotype frequencies differs between Graves' disease and controls (chi2 = 5.99, degrees of freedom = 2, p = 0.0386). We found overexpression of F allele (69% vs. 61%, p = 0.0472) and homozygote FF (48% vs. 33%, p = 0.0118) in Graves' disease patients compared with controls. We also correlated a VDR-FokI polymorphism with BMD in the distal radius and biochemical markers of bone turnover in patients with Graves' disease in remission. Although generally no significant association was seen between age-adjusted BMD and genotype, patients in remission for >5 years showed significantly lower age-adjusted BMD in Ff heterozygotes than in ff homozygotes (Z = 1.14 ff vs. Z = -0.43 Ff, p < 0.05). Moreover, serum concentrations of bone alkaline phosphatase were significantly greater in Ff homozygotes than in FF homozygotes (78 +/- 12 vs. 59 +/- 10, p < 0.05). The genotypes did not differ in serum concentrations of osteocalcin, urinary hydroxyproline, or urinary deoxypyridinoline. Our results indicate, for the first time, an association between Graves' disease and a VDR polymorphism in the Japanese and suggest that a VDR-FokI polymorphism may affect bone mineral metabolism and can predict risk of osteoporosis as a complication of Graves' disease in patients in remission.

Interaction of the effects between vitamin D receptor polymorphism and exercise training on bone metabolism

Bone metabolism is strongly influenced by heredity and environmental factors. To investigate interaction of the effects between vitamin D receptor polymorphism by Fok I and resistance exercise training on bone metabolism, young male subjects with FF genotype (F, n = 10) and Ff or ff genotypes (f, n = 10) followed 1 mo of weight training, and changes in bone metabolism were compared. An additional 14 subjects served as a sedentary control. Biomarkers of bone formation, bone-specific alkaline phosphatase, and osteocalcin were significantly increased by training in both F and f groups. 1, 25-Dihydroxyvitamin D(3), known to upregulate bone formation, was also increased by the training in the f but not in the F group. Bone resorption assessed by cross-linked NH(2)-terminal telopeptide of type I collagen was significantly suppressed by the training, and the decrease in F was greater and longer lasting than that in f group. In conclusion, stimulation of bone formation and suppression of bone resorption occurred within 1 mo in young men. Despite a significant increase in 1,25-dihydroxyvitamin D(3) in the f group but not in the F group, the response of bone metabolism to the training in the F was similar to or greater than that in f group, suggesting a functional difference between vitamin D receptor genotypes f and F.

Vitamin D receptor gene polymorphism is associated with birth height, growth to adolescence, and adult stature in healthy caucasian men: a cross-sectional and longitudinal study

Vitamin D receptor (VDR) polymorphism has been associated with bone mineral density (BMD), but recent data indicate association to parameters of body constitution and growth. We investigated VDR gene polymorphism, defined by BsmI and TaqI, in 90 healthy Caucasian males and any relation with parameters of body constitution at birth, and to parameters of body constitution, BMD and bone area, at age 16.9 +/- 0.3 yr (mean +/- SD) and at age 19.2 +/- 0.7. Using PCR and the restriction enzyme BsmI and TaqI, the allelic variants BB, Bb, and bb, and TT, Tt, and tt were identified. Height (cm) and weight (kg) were measured using standardized equipment, and BMD of the total body, lumbar spine, and femoral neck, and bone area (cm2) of the total body, humerus, femur was measured using dual-energy x-ray absorptiometry. BsmI and TaqI genotypes were related in 89 of the 90 cases; hence, the same associations were found for both genotypes. Boys with the BB genotype were shorter at birth (P = 0.01) and grew less from birth to age 16.9 +/- 0.3 (P = 0.01) than their Bb and bb counterparts. Both during puberty (age 16.9 +/- 0.3) and after puberty (age 19.3 +/- 0.7), the BB boys were shorter (P = 0.005-0.008) and had lower bone area of the humerus, femur, and total body (P < 0.05) than the Bb and bb boys. The allelic variants were not related to BMD at any site. A prediction model including parental height, birth height, birth weight, and VDR alleles could predict up to 39% of the total variation in adult height in our population. The VDR allelic variants alone contributed to 8% of the total variation.

Genetic epidemiological approaches to the search for osteoporosis genes

Important progress has been made in the identification of specific environmental factors and estimation of hereditary components in bone density, quantitative ultrasound (QUS), and bone turnover indices. By contrast, the search for specific genes that regulate bone mass has progressed rather slowly, and the results are more difficult to interpret and reproduce. This article reviews the genetics of osteoporosis and problems plaguing genetic research. It is argued that the search for genes involved in the expression of osteoporotic phenotypes should be based on linkage studies in relatively homogeneous populations. Strategies for increasing the power of studies, such as making use of information from extended pedigrees and multivariate analysis, are discussed. With the advent of a comprehensive human genetic linkage map, a complete identification of genes for osteoporosis appears feasible. Understanding the genetic mechanisms and their interactions with environmental factors should allow more focused and cost-effective osteoporosis prevention and treatment strategies.

The polymorphic N terminus in human vitamin D receptor isoforms influences transcriptional activity by modulating interaction with transcription factor IIB

The human vitamin D receptor (hVDR) is a ligand-regulated transcription factor that mediates the actions of the 1,25-dihydroxyvitamin D3 hormone to effect bone mineral homeostasis. Employing mutational analysis, we characterized Arg-18/Arg-22, hVDR residues immediately N-terminal of the first DNA binding zinc finger, as vital for contact with human basal transcription factor IIB (TFIIB). Alteration of either of these basic amino acids to alanine also compromised hVDR transcriptional activity. In contrast, an artificial hVDR truncation devoid of the first 12 residues displayed both enhanced interaction with TFIIB and transactivation. Similarly, a natural polymorphic variant of hVDR, termed F/M4 (missing a FokI restriction site), which lacks only the first three amino acids (including Glu-2), interacted more efficiently with TFIIB and also possessed elevated transcriptional activity compared with the full-length (f/M1) receptor. It is concluded that the functioning of positively charged Arg-18/Arg-22 as part of an hVDR docking site for TFIIB is influenced by the composition of the adjacent polymorphic N terminus. Increased transactivation by the F/M4 neomorphic hVDR is hypothesized to result from its demonstrated enhanced association with TFIIB. This proposal is supported by the observed conversion of f/M1 hVDR activity to that of F/M4 hVDR, either by overexpression of TFIIB or neutralization of the acidic Glu-2 by replacement with alanine in f/M1 hVDR. Because the f VDR genotype has been associated with lower bone mineral density in diverse populations, one factor contributing to a genetic predisposition to osteoporosis may be the F/f polymorphism that dictates VDR isoforms with differential TFIIB interaction.

[Multiple genetic typing (vitamin D receptors and estrogens) in the assessment of the risk of fractures]

BACKGROUND

Several studies suggested that some vitamin D receptor (VDR) and estrogen receptor (ER) polymorphisms influence bone mass. However, others did not confirm these results. This study was undertaken to determine if the genotypes revealed by the combined analysis of VDR and ER polymorphisms are associated with clinically significant differences in peak bone mass and the risk of osteoporotic fractures.

PATIENTS AND METHODS

Restriction fragment length polymorphisms of VDR were determined with the enzymes Bsml, Apal, Taql, and Fokl. Enzymes Xbal and Pvull were used as polymorphic markers of the ER. The study group comprised 149 young control women (18-34 years), 66 postmenopausal controls, 99 women with hip fracture and 76 women with osteoporotic vertebral fractures. Bone mineral density (BMD) was measured by DEXA.

RESULTS

We did not find significant differences in lumbar spine or hip BMD among young women with different genotypes (determined with either single or multiple polymorphic markers). Likewise, there were no differences in the frequency distributions of VDR or ER alleles between control and fractured women. The study had a 77% power to detect a fracture odds ratio of 2 in case of genotypes present in at least 15% of the population.

CONCLUSIONS

These results suggest that the polymorphic markers used in this study do not have enough discriminant power to be clinically useful in the assessment of fracture risk.

Vitamin D receptor gene polymorphisms and the risk of fractures in older women. For the Study of Osteoporotic Fractures Research Group

The association between vitamin D receptor gene polypmorphisms and bone mineral density is controversial. The relationship between vitamin D receptor genotype and risk of fracture is uncertain. To determine whether vitamin D receptor polymorphisms were associated with the risk of hip, vertebral, and other (nonhip, nonvertebral) fractures in elderly women, we conducted a case-cohort study within a prospective study of 9704 community-dwelling women aged 65 years and older. Vitamin D receptor allele and genotype frequencies in women who experienced first incident hip (n = 181), vertebral (n = 127), and other (n = 223) fractures were compared with those of control women selected randomly from the cohort. Average length of follow-up was 6.5, 3.7, and 5.4 years for women in hip, vertebral, and other fracture analyses, respectively. Vitamin D receptor polymorphisms were determined by polymerase chain reaction amplification of genomic DNA using TaqI and ApaI restriction site endonuclease digestion. All nonvertebral fractures were confirmed by X-ray reports; hip fractures were validated by review of X-ray films. Vertebral fractures were defined by morphometry using lateral spine radiography at baseline and an average of 3.7 years later. Allele or genotype frequencies did not differ between fracture cases and their respective controls. Vitamin D receptor genotype (defined by TaqI, ApaI, or the combination of TaqI and ApaI) was not significantly associated with the risk of hip, vertebral, or other fractures. For example, compared with the referent group of women with TT genotype, those with Tt and tt genotypes had similar age- and weight-adjusted risks of fracture at the hip (hazard ratios 0.9, 95% confidence interval [CI] 0.6-1.3, and 0.8, 95% CI 0.5-1.2, respectively), spine (odds ratios 1.1, 95% CI 0.7-1.8, and 0.7, 95% CI 0.4-1.3, respectively), or other skeletal site (hazard ratios 1.0, 95% CI 0. 7-1.4, and 1.0, 95% CI 0.7-1.5, respectively). These findings were not altered in additional analyses including those adjusted for and stratified by age, ethnic ancestry, calcaneal bone density, dietary calcium intake, use of calcium supplements, use of vitamin D supplements, and oral estrogen use. We conclude that Vitamin D receptor polymorphisms defined by TaqI and ApaI are not associated with the risk of fracture in older women. Our results suggest that determination of these vitamin D receptor polymorphisms is not a clinically useful test for the prediction of fracture risk in elderly women.

FokI polymorphism at translation initiation site of the vitamin D receptor gene predicts bone mineral density and vertebral fractures in postmenopausal Italian women

A novel T/C polymorphism (ATG to ACG) at the translation initiation site of the vitamin D receptor (VDR) gene, defined by FokI restriction endonuclease, has been recently associated with variation in bone mineral density (BMD) and rates of bone loss in a group of postmenopausal Mexican-American women. The presence of the restriction site, designated as f, allows protein translation to initiate from the first ATG, while the allele lacking the site, indicated as F, initiates translation at a second ATG. In this study, we investigated the role of FokI polymorphism in a group of 400 postmenopausal women of Italian descent stratified for BMD into osteoporotic (n = 164), osteopenic (n = 117), and normal (n = 119) groups. There were 159 (41%) FF homozygotes, 55 (14%) ff homozygotes, and 186 (45%) Ff heterozygotes. In the whole population, we observed a weak association between FokI polymorphism and lumbar BMD (p = 0.06, analysis of covariance [ANCOVA]) but not with femoral neck BMD (p = 0.5, ANCOVA). Interestingly, the effect of FokI genotypes on lumbar BMD was influenced by the years since menopause such that differences in BMD related to different VDR allelic variants were greater among women in the first 5 years of menopause (p = 0.04, ANCOVA), progressively declining afterward. In addition, a significantly higher prevalence of ff genotype in osteoporotic than in osteopenic and normal women was observed (p = 0.04, Chi-square test). Finally, ff genotype resulted significantly over-represented in the group of women with a vertebral fracture as compared with controls (p = 0.003, Chi-square test), equivalent to a relative risk of 2.58 (95% confidence intervals 1.36-4.91). We conclude that in this population, FokI polymorphism at the VDR gene locus accounts for a part of the heritable component of BMD at the lumbar spine.

The vitamin D receptor (VDR) start codon polymorphism in primary hyperparathyroidism and parathyroid VDR messenger ribonucleic acid levels

Vitamin D regulates parathyroid cell proliferation and secretion of PTH. Increased prevalence of the polymorphic vitamin D receptor (VDR) alleles b, a, and T has been reported in sporadic primary hyperparathyroidism (PHPT), suggesting that these genetic variants may predispose to the disease. Recently, another polymorphism in the VDR gene was related to bone mineral density, and this VDR-FokI polymorphism causes different lengths of the VDR, implying possible functional consequences. The VDR-FokI polymorphism was studied in 182 postmenopausal women with sporadic PHPT and in matched controls. No significant differences in distribution of the VDR-FokI genotypes could be detected between the groups, although there was a tendency toward overrepresentation of the F allele in the PHPT patients (P = 0.05). There were no significant associations with age, serum calcium, serum PTH, bone mineral density, or parathyroid tumor weight. The VDR genotypes were unrelated to VDR and PTH messenger ribonucleic acid levels in the parathyroid adenomas of 42 PHPT patients. In 23 PHPT patients, the Ca2+-PTH set-points were determined in vivo and were unrelated to the VDR alleles. We suggest that the VDR-FokI polymorphism has at most a minor pathogenic importance in the development of PHPT.

Vitamin D receptor gene Fok1 polymorphism predicts calcium absorption and bone mineral density in children

The vitamin D receptor (VDR) gene has been implicated as one of the major genetic components of osteoporosis. We evaluated the relationship between markers of mineral status and restriction fragment length polymorphisms of the VDR gene in 72 healthy children age 7-12 years. Using stable isotope techniques and dual-energy X-ray absorptiometry, we measured dietary calcium absorption, bone calcium deposition rates, and total body bone mineral density (BMD). The Fok1 polymorphism at the VDR translation initiation site was significantly associated with BMD (p = 0.02) and calcium absorption (p = 0.04). Children who were FF homozygotes had a mean calcium absorption that was 41.5% greater than those who were ff homozygotes and 17% greater absorption than Ff heterozygotes. BMD was 8.2% greater in the FF genotype than the ff genotype and 4.8% higher than the Ff genotype. These results suggest a substantial relationship between the VDR gene and bone metabolism at one or more levels, including dietary absorption of calcium and BMD in growing children.

The vitamin d receptor gene and calcium metabolism

Dietary Ca(2+) is essential for the development and maintenance of bone mineral mass. The vitamin D endocrine system plays a fundamental role in the regulation of Ca(2+) homeostasis, and mutations affecting genes implicated in vitamin D metabolism or vitamin D receptor (VDR) functions are responsible for severe alterations in skeletal growth. In addition, vitamin D is also implicated in the pathophysiology and treatment of adult bone disorders associated with impaired mineralization of bone matrix. Very recently, common polymorphisms in the 3'- and 5'-end region of the VDR gene have been suggested as possible determinants of bone mineral mass and, hence, of the risk of osteoporosis. None of these polymorphisms appear to be associated unequivocally with bone mineral mass or biochemical variables of Ca(2+) and phosphate metabolism, except perhaps VDR 3'-end polymorphisms before puberty. As these associations are so inconsistent, interactions with environmental factors, particularly dietary intake, and with other polymorphisms have to be considered.

Heritable and nutritional influences on bone mineral mass

Osteoporosis is the net result of the maximal amount of bone mineral mass achieved by the end of pubertal growth (peak bone mass) minus post-menopausal and elderly bone losses. Peak bone mineral mass is determined from early childhood by both heritable and environmental factors. Recent developments in the molecular epidemiology of osteoporosis have shown the interest, but also the limitations, of specific molecular markers, such as the vitamin D receptor gene polymorphisms Bsm 1 and Fok 1, to explain bone mineral density differences across the population. Importantly, however, interactions between VDR gene polymorphisms and environmental factors, particularly dietary calcium, have provided new insights into the complex determination of bone mineral mass.