The association of bone mineral density with vitamin D receptor gene polymorphisms

It starts from the womb: maximizing bone health

The foundation of bone health is established in utero. Bone accrual starts from the developing fetus and continues throughout childhood and adolescence. This process is crucial to achieve peak bone mass. Understanding factors that influence bone accrual before attainment of peak bone mass is thus critical to improve bone health and prevent osteoporosis, thereby reducing the burden of osteoporotic fractures in older women. In this review, we broadly outline factors influencing peak bone mass from pregnancy to infancy, childhood and adolescence with potential diseases and medications that may affect the optimum trajectory to maximizing bone health. It is estimated that a 10% increase in peak bone mass will delay the onset of osteoporosis by 13 years in a woman.

Relationship between vitamin D receptor gene polymorphisms (BsmI, TaqI, ApaI, and FokI) and calcium intake on bone mass in young Japanese women

Background

The high prevalence of low bone mass in young women in Japan has emerged as a serious health issue in recent years. Therefore, the aim of the present study was to reevaluate the relationship between genetic and dietary factors, as well as its influence on bone mass in young Japanese women, with particular emphasis on vitamin D receptor (VDR) gene polymorphisms and calcium intake.

Methods

A total of 499 Japanese women aged 20–24 years were enrolled in the study. The bone mass of the calcaneus was assessed using the quantitative ultrasound method and expressed as the osteo sono-assessment index (OSI). VDR gene polymorphisms (BsmI, TaqI, ApaI, and FokI) were analyzed using DNA extracted from saliva. Calcium intake was assessed using the Food Frequency Questionnaire based on food groups (FFQg) and adjusted with the energy intake. Participants were divided into two groups based on the median calcium intake (250 mg/1000 kcal).

Results

Consequently, bone mass was significantly different among the BsmI and TaqI genotypes after adjusting for body mass index (BMI) (p = 0.030 and 0.019, respectively). In addition, the BsmI AA and ApaI GT genotypes showed significant differences in bone mass between the calcium-intake groups, with low OSI in the low-calcium intake group and high OSI in the high-calcium intake group, respectively, even after adjusting for BMI (p = 0.020 and 0.038, respectively).

Conclusions

These findings may prove instrumental in developing a logical approach towards preventing bone loss in young Japanese women.

Association of vitamin D receptor gene polymorphism (TaqI and Apa1) with bone mineral density in North Indian postmenopausal women

Vitamin D receptor (VDR) gene has an important role as a candidate gene for the regulation of bone mass in osteoporosis. However, its association with bone mineral density (BMD) is controversial and has not been established in different ethnic populations. To enhance the understanding of VDR gene polymorphism in the context of BMD, we investigated the plausible genetic association of TaqI and ApaI polymorphism with BMD in North Indian postmenopausal women with osteoporosis.254 osteoporotic women (Age 55.82 ± 6.91) and 254 postmenopausal non osteoporotic women (Age 54.76 ± 6.26) were included in the study. VDR TaqI and ApaI polymorphism were determined by PCR (polymerase chain reaction) and RFLP (restriction fragment length polymorphism). BMD was assessed by dual energy X-ray absorptiometry (DXA) at the lumbar spine (L₁-L₄), hip, forearm and femoral neck. The average BMD with TT genotype was significantly lower at lumbar spine, hip and forearm. The Frequency of TT genotype and t allele was significantly high in osteoporotic women when compared with controls. The average BMD with Aa genotype was higher in ApaI. Furthermore, comparison of frequency distribution of genotype and allele for VDR ApaI between osteoporotic patients and controls did not show any significant difference. Our findings revealed that TaqI gene TT genotype was associated with low BMD in North Indian osteoporotic women. Moreover, TT genotype and t allele associated significantly with osteoporosis in postmenopausal women. Therefore, VDR TaqI gene is an important determinant of risk factor for osteoporosis.

Causes of low peak bone mass in women

Peak bone mass is the maximum bone mass that accrues during growth and development. Consolidation of peak bone mass normally occurs during early adulthood. Low peak bone mass results from failure to achieve peak bone mass genetic potential, primarily due to bone loss caused by a variety of conditions or processes occurring at younger ages than usual. Recognized causes of low peak bone mass include genetic causes, endocrine disorders, nutritional disorders, chronic diseases of childhood or adolescence, medications, and idiopathic factors.

Use of Genetic Algorithm Combinational Single-nucleotide Polymorphisms Could Modify the Association of Blood Lead Levels and Bone Matrix Density

BACKGROUND

Previous studies have not explored the relationship between a single gene and a single disease. Our study aims to investigate the association of multiple genotypes with blood lead levels and bone matrix density (BMD) by using genetic algorithms.

METHODS

Our research focused on 506 employees (245 males and 261 females) of a lead battery factory in Taiwan. We collected data on their BMD, blood lead level, and 6 SNPs (ACE, alpha-adducin, Bsm, Tag, Apa, and ALAD); these factors were analyzed using discrete binary particle swarm optimization (DBPSO) and logistic regression analysis.

RESULTS

We found no association between blood lead level and bone density, which may be due to the relatively young age of this population (mean age = 45.1 years). However, the genotype that contained both Bsm type bb and ALAD type 1-1 may play an important role in protecting against lower bone density among these employees.

CONCLUSIONS

In conclusion, this study found that the Bsm and ALAD genes influence bone density among lead workers. However, the mechanism and exact relationship between these two genes and bone density require further investigation.

Association between the vitamin D receptor gene polymorphism and osteoporosis

The influence of the vitamin D receptor (VDR) gene for the risk of osteoporosis remains to be elucidated. The aim of the present study was to understand the distribution of various single-nucleotide polymorphisms (SNPs) within the VDR gene and its association with the risk of osteoporosis. In total, 378 subjects without a genetic relationship were recruited to the study between January 2013 and July 2015. The subjects were divided into three groups, which were the normal (n=234), osteoporosis (n=65) and osteoporosis with osteoporotic fracture (n=79) groups. Three pertinent SNPs of the VDR gene rs17879735 (ApaI, Allele A/a, SNP C>A) were examined with polymerase chain reaction-restriction fragment length polymorphism. The bone mineral density (BMD) of the lumbar spine (L2-L4), femoral neck, Ward's and Tro was measured using dual-energy X-ray absorptiometry. The distributions of genotype frequencies aa, AA and Aa were 48.68, 42.86 and 8.46%, separately. Following analysis of each site, BMD, body mass index (BMI) and age, BMD for each site was negatively correlated with age (P<0.01) and positively correlated with BMI (P<0.01). Correction analysis revealed that there were significant differences in the Ward's triangle BMD among each genotype (P<0.05), in which the aa genotype exhibited the lower BMD (P<0.05). No significant difference was identified among the different genotypes in the occurrence of osteoporosis with osteoporotic fracture (P>0.05). In conclusion, these indicated that the VDR gene ApaI polymorphisms had an important role in the osteoporosis risk.

Lack of Influence of Vitamin D Receptor BsmI (rs1544410) Polymorphism on the Rate of Bone Loss in a Cohort of Postmenopausal Spanish Women Affected by Osteoporosis and Followed for Five Years

A longitudinal study was conducted to investigate the relation between a polymorphism in the vitamin D receptor (VDR) gene and changes in bone mineral density (BMD) and quantitative ultrasound of the phalanges (QUS) over a five-year period. The subjects were 456 postmenopausal women with osteoporosis undergoing treatment, aged 59.95±7.97 years (mean±standard deviation [SD]) at baseline. BMD was measured at the hips and lumbar spine by dual-energy X-ray absorptiometry, and QUS was measured by means of amplitude-dependent speed of sound (Ad-SoS) at the phalanges. Lifestyle information was obtained via a questionnaire. The genotype frequencies of the BsmI (rs1544410) gene polymorphism were 29.4%, 47.1%, and 23.5% for bb, Bb, and BB, respectively. After five years, BMD (annual change in %/year) at the femoral neck (FN) showed a significant modification based on the rs1544410 genotype (BB vs Bb); there was an overall decrease in bone mass (-0.70±2.79%/year; P = 0.025). An analysis of covariance with adjustments for age, weight, height, percentage of weight change per year, baseline BMD and calcium intake showed that the observed associations were no longer significant (P = 0.429). No significant associations were found between the QUS measurements and the rs1544410 genotype after the five-year period. Our study limitations includes lack of information about type and length of duration of the osteoporosis treatment. Our results indicate that rs1544410 polymorphisms do not account significantly for the changes in bone mass in Spanish women with osteoporosis undergoing treatment.

Polymorphisms in VDR gene in Tunisian postmenopausal women are associated with osteopenia phenotype

OBJECTIVES

Osteopenia is characterized by intermediate values of bone mineral density (BMD) as compared to normal and osteoporotic subjects. BMD, a surrogate phenotype for osteoporosis, is influenced in part by genetic factors. Among the genes associated with BMD, the vitamin D receptor (VDR) was the first gene studied as a potential candidate associated with BMD in adult and postmenopausal bone loss. However, results are controversial.

METHODS

To determine whether VDR polymorphisms ApaI and TaqI are associated with BMD, osteopenia, osteoporosis and low-impact fracture risk in North Africans, these genotypes were analyzed in 566 postmenopausal Tunisian women.

RESULTS

In postmenopausal Tunisian women, the GT ApaI genotype seems to be protective against osteoporosis development (p = 0.02; odds ratio = 0.54). Moreover, the presence of the combined GT/TT genotype of ApaI and TaqI polymorphisms is more frequent in normal BMD women than in osteoporotic women (p = 0.00; odds ratio = 0.41). Interestingly, the GG ApaI genotype is associated with osteopenia development (p = 0.02; odds ratio = 1.86) and also the TT TaqI polymorphism (p = 0.02; odds ratio = 1.53). The GG ApaI genotype is associated with a three times risk of vertebral fracture.

CONCLUSIONS

The ApaI polymorphism showed an association with osteopenia and low-impact vertebral fracture incidence but not with osteoporosis. The TaqI polymorphism is associated specifically with the osteopenia phenotype. The presence of the two polymorphisms increases the risk to develop osteopenia in postmenopausal Tunisian women. Osteopenia seems to be genetically determined. However, osteoporosis is the result of interaction between genetic and environmental factors.

The effect of FokI vitamin D receptor polymorphism on bone mineral density in Jordanian perimenopausal women

CONTEXT:

Osteoporosis is a polygenic, multifactorial disease that is characterized by demineralization of bone, and thus presented with decreasing bone mineral mass. Vitamin D receptor (VDR) gene polymorphisms in the 3’-end region (as determined by the enzymes BsmI and ApaI) have been inconsistently associated with bone mineral mass. Another important VDR start codon polymorphism (as determined by the enzyme FokI) has been found to be related to adult bone mineral density (BMD) in pre-and post-menopausal American women.

AIMS:

This study aims to investigate the prevalence of the FokI VDR gene polymorphism in Jordanian perimenopausal women and study its relationship with bone mineral density.

MATERIALS AND METHODS:

DNA was isolated from 90 controls (Mean age = 50.41 ± 1.29 y), and 120 patients with symptomatic vertebral fractures (Mean age = 49.14 ± 3.19 y). Restriction Fragment Length Polymorphism (RFLP) analysis of FokI was performed on DNA samples.

STATISTICAL ANALYSIS:

Data was analyzed using SPSS v19 and Microsoft Excel 2007.

RESULTS:

The results showed that in controls, the FF (−0.70 ± 0.51) genotype is associated with high lumbar spine BMD Z-score as compared to Ff (−1.25 ± 0.26) and ff (−1.66 ± 0.47) genotypes (P = 0.0095). In patients, the ff genotype was associated with lower lumbar spine BMD in T-score (−2.31 ± 0.17) and Z-score (−1.56 ± 0.09) genotypes (P = 0.031). No significant association was seen in the femoral neck BMD.

CONCLUSION:

FokI polymorphism may be associated with low BMD in our studied population; however, further studies including other polymorphisms and large sample number are needed.

Vitamin D receptor (VDR) gene polymorphism influences the risk of osteoporosis in postmenopausal women of Northwest India

SUMMARY

The influence of VDR gene for the risk of osteoporosis has remained inconclusive. VDR gene polymorphism in relation to BMD in postmenopausal women of Northwest India revealed a susceptibility haplotype AGT. Possession of this haplotype exacerbates the risk of osteoporosis by 2.8 times, which manifests in recessive mode of inheritance.

PURPOSE

The purpose of this study is to understand the influence of coordinated effect of various single nucleotide polymorphisms (SNPs) within vitamin D receptor (VDR) gene for the risk of osteoporosis, which has remained undefined so far.

METHODS

Four pertinent SNPs of VDR gene, i.e., rs2228570, rs1544410, rs17879735, and rs731236 were examined with polymerase chain reaction-restriction fragment length polymorphism in dual energy X-ray absorptiometry verified 188 osteoporotics, 115 osteopenics, and 147 normal postmenopausal women of Northwest India.

RESULTS

Minor allele 'T' of rs2228570 showed significant influence for the risk of osteoporosis (OR 1.60, 95%CI 1.16-2.20, P=0.004) and also in dominant (OR 2.32, 95%CI 1.47-3.64, P=0.0006) and additive model (OR 2.41, 95%CI 1.49-3.87, P=0.0006) after Bonferroni correction. Minor allele (T) of rs2228570 showed an allele dose effect with BMD of L1-L4 (P=0.009) and FN (P=0.036). Disease association analysis exposed a susceptibility haplotype AGT which influences the risk of osteopenia (OR 2.04, 95%CI 1.03-4.08, P=0.036) and osteoporosis (OR 2.90, 95%CI 1.61-5.38, P=0.00005) after adjusting the effects of age, BMI and years since menopause. This haplotype is significantly associated with BMDs at lumbar spine (P=0.0001) and femoral neck (P=0.016).

CONCLUSION

In-depth analysis of this haplotype with other methods of Wald statistics and Akaike information criterion confirmed that carriers of each unit of this haplotype AGT increases the risk of osteoporosis by a factor of 2.80±0.34 (β±SE) which manifests (P=0.1 × 10⁻⁶) in its recessive mode of inheritance.

Genetic variants and associations of 25-hydroxyvitamin D concentrations with major clinical outcomes

CONTEXT

Lower serum 25-hydroxyvitamin D concentrations are associated with greater risks of many chronic diseases across large, prospective community-based studies. Substrate 25-hydroxyvitamin D must be converted to 1,25-dihydroxyvitamin D for full biological activity, and complex metabolic pathways suggest that interindividual variability in vitamin D metabolism may alter the clinical consequences of measured serum 25-hydroxyvitamin D.

OBJECTIVE

To investigate whether common variation within genes encoding the vitamin D-binding protein, megalin, cubilin, CYP27B1, CYP24A1, and the vitamin D receptor (VDR) modify associations of low 25-hydroxyvitamin D with major clinical outcomes.

DESIGN, SETTING, AND PARTICIPANTS

Examination of 141 single-nucleotide polymorphisms in a discovery cohort of 1514 white participants (who were recruited from 4 US regions) from the community-based Cardiovascular Health Study. Participants had serum 25-hydroxyvitamin D measurements in 1992-1993 and were followed up for a median of 11 years (through 2006). Replication meta-analyses were conducted across the independent, community-based US Health, Aging, and Body Composition (n = 922; follow-up: 1998-1999 through 2005), Italian Invecchiare in Chianti (n = 835; follow-up: 1998-2000 through 2006), and Swedish Uppsala Longitudinal Study of Adult Men (n = 970; follow-up: 1991-1995 through 2008) cohort studies.

MAIN OUTCOME MEASURE

Composite outcome of incident hip facture, myocardial infarction, cancer, and mortality over long-term follow-up.

RESULTS

Interactions between 5 single-nucleotide polymorphisms and low 25-hydroxyvitamin D concentration were identified in the discovery phase and 1 involving a variant in the VDR gene replicated in independent meta-analysis. Among Cardiovascular Health Study participants, low 25-hydroxyvitamin D concentration was associated with hazard ratios for risk of the composite outcome of 1.40 (95% CI, 1.12-1.74) for those who had 1 minor allele at rs7968585 and 1.82 (95% CI, 1.31-2.54) for those with 2 minor alleles at rs7968585. In contrast, there was no evidence of an association (estimated hazard ratio, 0.93 [95% CI, 0.70-1.24]) among participants who had 0 minor alleles at this single-nucleotide polymorphism.

CONCLUSION

Known associations of low 25-hydroxyvitamin D with major health outcomes may vary according to common genetic differences in the vitamin D receptor.

Tea and coffee consumption in relation to vitamin D and calcium levels in Saudi adolescents

BACKGROUND

Coffee and tea consumption was hypothesized to interact with variants of vitamin D-receptor polymorphisms, but limited evidence exists. Here we determine for the first time whether increased coffee and tea consumption affects circulating levels of 25-hydroxyvitamin D in a cohort of Saudi adolescents.

METHODS

A total of 330 randomly selected Saudi adolescents were included. Anthropometrics were recorded and fasting blood samples were analyzed for routine analysis of fasting glucose, lipid levels, calcium, albumin and phosphorous. Frequency of coffee and tea intake was noted. 25-hydroxyvitamin D levels were measured using enzyme-linked immunosorbent assays.

RESULTS

Improved lipid profiles were observed in both boys and girls, as demonstrated by increased levels of HDL-cholesterol, even after controlling for age and BMI, among those consuming 9-12 cups of coffee/week. Vitamin D levels were significantly highest among those consuming 9-12 cups of tea/week in all subjects (p-value 0.009) independent of age, gender, BMI, physical activity and sun exposure.

CONCLUSION

This study suggests a link between tea consumption and vitamin D levels in a cohort of Saudi adolescents, independent of age, BMI, gender, physical activity and sun exposure. These findings should be confirmed prospectively.

Nervous system autoantibodies and vitamin D receptor gene polymorphisms in hemodialysis patients

Cognitive deficits are prevalent in hemodialysis (HD) patients. Vitamin D deficiency and vitamin D receptor (VDR) gene single nucleotide polymorphism (SNPs) have been linked to both neurodegeneration (ND) and neuroprotection, respectively. Autoantibodies (Ab) to myelin basic protein (MBP), glial fibrillary acidic protein (GFAP), and neurofilament (NF) triplet proteins arise secondary to nervous system (NS) damage providing a means to assess neurological injury. Characterization of Ab biomarkers of NS damage in HD patients, their association with VDR SNPs, and nutritional vitamin D (NVD) therapy was performed. VDR genotypes, cytokines, and Ab biomarkers to NS proteins in HD subjects receiving ergocalciferol (n = 40) were compared with nonusers (n = 71). Interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and immunoglobulin G (IgG) titers against NFs, GFAP, and MBP were measured by immunoassay. Subjects were genotyped for VDR SNPs BsmI (rs1544410) and FokI (rs2228570). Subjects (age 63.3 ± 16.1 years, 66% male) who were C allele carriers of BsmI had higher values of NF-68 antibody titers (p = 0.027). Ergocalciferol users (n = 40) compared with nonusers (n = 71) had lower Ab titers to NS proteins; however, only anti-NF-160 and anti-MBP titers were significantly (p < 0.05) higher. IgG against NS proteins in HD patients suggests neuronal and glial insult and a relationship with VDR alleles. NVD may provide some neuroprotection, indicated by anti-NF-160 and anti-MBP, which was markedly lowered in ergocalciferol patients. This preliminary study suggests that Ab detection may be useful in monitoring ND and the potential of NVD for neuroprotection in HD patients.

Strigolactones: a novel class of phytohormones that inhibit the growth and survival of breast cancer cells and breast cancer stem-like enriched mammosphere cells

Several naturally occurring phytohormones have shown enormous potential in the prevention and treatment of variety of different type of cancers. Strigolactones (SLs) are a novel class of plant hormones produced in roots and regulate new above ground shoot branching, by inhibiting self-renewal of undifferentiated meristem cells. Here, we study the effects of six synthetic SL analogs on breast cancer cell lines growth and survival. We show that SL analogs are able to inhibit proliferation and induce apoptosis of breast cancer cells but to a much lesser extent "non-cancer" lines. Given the therapeutic problem of cancer recurrence which is hypothesized to be due to drug resistant cancer stem cells, we also tested the ability of SL analogs to inhibit the growth of mammosphere cultures that are typically enriched with cancer stem-like cells. We show that SLs are potent inhibitors of self-renewal and survival of breast cancer cell lines grown as mammospheres and even a short exposure leads to irreversible effects on mammosphere dissociation and cell death. Immunoblot analysis revealed that SLs analogs induce activation of the stress response mediated by both P38 and JNK1/2 MAPK modules and inhibits PI3K/AKT activation. Taken together this study indicates that SLs may be promising anticancer agents whose activities may be achieved through modulation of stress and survival signaling pathways.

Known VDR polymorphisms are not associated with bone mineral density measures in pediatric Cushing disease

Decreased bone mineral density (BMD) has been documented in adults with Cushing disease (CD), and allelic variants of the vitamin D receptor (VDR) gene have been associated with osteopenia. Genetic factors play an important role in bone accrual and its response to various diseases; among them, the most studied are the allelic variants of the VDR gene. There is debate as to whether described variants in the VDR gene have an effect on BMD. In the current study, we sought to analyze whether BMD differences in patients with CD were associated with the Taq1 and Apal VDR allelotypes. The data showed lack of association between BMD and these widely studied VDR polymorphisms, suggesting that the effect of endogenous hypercortisolism on bone in the context of CD does not depend on VDR genotypes.

Association between vitamin D receptor gene polymorphisms and bone mineral density in Chinese women

Vitamin D receptor (VDR) is implicated in the regulation of bone mineral density (BMD). In this study, we performed a meta-analysis to evaluate the association between the VDR BsmI (rs1544410) and ApaI (rs7975232) polymorphisms and BMD in Chinese women. Literature was retrieved from PubMed and other databases. The studies on the association between VDR BsmI and ApaI genotypes and BMD at the lumbar spine, the femoral neck, the trochanter or the Ward's triangle in Han Chinese women were included in this meta-analysis. Pooled BMD differences and 95% confidence intervals (CIs) were calculated using random- or fixed- effects model. Twenty-five eligible studies, which included 4,075 Chinese women, were identified. No significant difference was observed for either genotype when the meta-analysis was limited to premenopausal women. In postmenopausal women, BMD differences were significant for BB vs. Bb [-0.029 (95% CI -0.056, -0.002) g/m(2), P = 0.037] at the femoral neck, AA vs. Aa [-0.029 (95% CI -0.051, -0.006) g/m(2), P = 0.012] at the lumbar spine, and Aa vs. aa [0.022(95% CI 0.011, 0.033) g/m(2), P = 0.000] at the trochanter. These results suggest a modest but statistically significant association between VDR BsmI and ApaI polymorphisms and BMD in Chinese postmenopausal women, with higher BMD in heterozygous subjects. More epidemiological and mechanistic studies are needed to further investigate the role of VDR gene polymorphisms in regulating BMD and osteoporosis in the future.

Vitamin D receptor gene polymorphisms in a group of postmenopausal Turkish women: association wıth bone mineral density

OBJECTIVE

To determine the frequency of the vitamin D receptor (VDR) gene polymorphisms BsmI, ApaI, TaqI and FokI and their associations with bone mineral density (BMD) in postmenopausal Turkish women.

DESIGN

One hundred and thirty healthy postmenopausal women and 130 premenopausal healthy women acting as controls were included in the study. The BsmI, FokI, ApaI and TaqI polymorphisms in the VDR gene were studied by polymerase chain reaction-restriction fragment length polymorphism method. The BMD of the lumbar vertebrae and femur neck were measured by dual-energy X-ray absorptiometry. Comparisons between the groups were performed using the paired t-test and ANOVA. χ (2) or contingency tables were used to analyze qualitative results.

RESULTS

Genotypes BB, Bb and bb occurred in premenopausal women with frequencies of 16.92%, 50% and 33.08% and in postmenopausal women with frequencies of 16.92%, 56.15% and 26.92%, respectively. Genotypes FF, Ff, ff occurred in premenopausal women with frequencies of 47.69%, 42.31% and 10% and in postmenopausal women with frequencies of 50.77%, 42.31% and 6.92%, respectively. Genotypes AA, Aa, aa occurred in premenopausal women with frequencies of 23.85%, 56.15% and 20% and in postmenopausal women with frequencies of 26.15%, 46.15% and 27.70%, respectively. Genotypes TT, Tt and tt occurred in premenopausal women with frequencies of 37.69%, 45.38% and 16.92% and in postmenopausal women with frequencies of 39.23%, 45% and 15.38%, respectively. There was no difference in the frequencies of VDR gene polymorphisms between premenopausal and postmenopausal women. BMD measurements were not different between genotypes in premenopausal and postmenopausal women.

CONCLUSIONS

The VDR gene BsmI, FokI, ApaI and TaqI polymorphisms have no major influence on bone mineral density in our group of postmenopausal women.

(Sub)clinical cardiovascular disease is associated with increased bone loss and fracture risk; a systematic review of the association between cardiovascular disease and osteoporosis

Introduction

Both cardiovascular disease and osteoporosis are important causes of morbidity and mortality in the elderly. The co-occurrence of cardiovascular disease and osteoporosis prompted us to review the evidence of an association between cardiovascular (CV) disease and osteoporosis and potential shared common pathophysiological mechanisms.

Methods

A systematic literature search (Medline, Pubmed and Embase) was conducted to identify all clinical studies that investigated the association between cardiovascular disease and osteoporosis. Relevant studies were screened for quality according to guidelines as proposed by the Dutch Cochrane Centre and evidence was summarized.

Results

Seventy studies were included in this review. Due to a large heterogeneity in study population, design and outcome measures a formal meta-analysis was not possible. Six of the highest ranked studies (mean n = 2,000) showed that individuals with prevalent subclinical CV disease had higher risk for increased bone loss and fractures during follow-up compared to persons without CV disease (range of reported risk: hazard ratio (HR) 1.5; odds ratio (OR) 2.3 to 3.0). The largest study (n = 31,936) reported a more than four times higher risk in women and more than six times higher risk in men. There is moderate evidence that individuals with low bone mass had higher CV mortality rates and incident CV events than subjects with normal bone mass (risk rates 1.2 to 1.4). Although the shared common pathophysiological mechanisms are not fully elucidated, the most important factors that might explain this association appear to be, besides age, estrogen deficiency and inflammation.

Conclusions

The current evidence indicates that individuals with prevalent subclinical CV disease are at increased risk for bone loss and subsequent fractures. Presently no firm conclusions can be drawn as to what extent low bone mineral density might be associated with increased cardiovascular risk.

Candidate gene association studies

Candidate gene association studies aim to establish or characterise association between the genetic -variation occurring within a specific gene or locus and a phenotype. If the phenotype is quantitative, then the effect size is often measured as the difference between the genotype specific means or a per allele effect. When the phenotype is binary and the disease is either present or absent, the effect is summarised as a genotype specific risk or relative risk. This chapter focuses on methodology employed when a single or small number of genetic loci are being investigated for an association with a specific phenotype.

BsmI, TaqI, ApaI, and FokI polymorphisms in the vitamin D receptor gene and periodontitis: a meta-analysis of 15 studies including 1338 cases and 1302 controls

AIM

A meta-analysis was conducted in order to investigate the potential association of vitamin D receptor (VDR) gene polymorphisms with susceptibility to aggressive and chronic periodontal disease.

MATERIAL AND METHODS

A database search yielded a total of 15 studies involving 1338 cases and 1302 controls. Four polymorphisms were included in the meta-analysis: VDR TaqI (rs731236), VDR BsmI (rs1544410), VDR FokI (rs2228570), and VDR ApaI (rs7975232). Odds ratios (ORs) along with their 95% confidence intervals (CIs) were computed to compare the distribution of alleles and genotypes between cases and controls.

RESULTS AND CONCLUSIONS

The combined results based on all studies showed that (1) chronic periodontitis cases had a significantly lower frequency of bb genotype of BsmI [OR=0.63, 95% CI=0.42, 0.94; p=0.02] in Asians; (2) chronic periodontitis cases had a significantly higher frequency of AA genotype of ApaI (OR=2.20, 95% CI=1.39, 3.48; p<0.001) in Asians; (3) chronic periodontitis cases had a weak significantly higher frequency of TT genotype of TaqI (OR=1.86, 95% CI=1.002, 3.46; p=0.049) in Asians. After Bonferroni's correction, we found that in Asians chronic periodontitis cases still had a significantly higher frequency of AA genotype of ApaI. No significant difference was found in any genotype of FokI. No association was found for all the VDR gene polymorphisms examined as far as the aggressive form of the disease is concerned. Future studies need to focus on the possible biological consequences and mechanisms of the VDR genetic variants. The current findings confirm that VDR gene is a candidate gene for periodontitis.

BsmI, TaqI, ApaI and FokI polymorphisms in the vitamin D receptor (VDR) gene and risk of fracture in Caucasians: a meta-analysis

CONTEXT

Vitamin D receptor (VDR) gene polymorphisms have been strongly associated with bone mineral density in some studies. However, in a recent meta-analysis, no relationship of the VDR BsmI or TaqI polymorphism and fracture risk was found in the meta-analysis of published data.

OBJECTIVE AND DESIGN

Our meta-analysis studied whether a relationship exists between BsmI, TaqI, ApaI and FokI polymorphisms in the VDR gene and risk of fracture.

DATA SOURCES

Relevant studies were identified from the following electronic databases: MEDLINE, EMBASE and Current Contents before January 2010.

DATA SYNTHESIS

This meta-analysis included 17 studies with a total of 21 eligible comparisons, which included 2112 fracture cases and 4521 controls. All of these studies reported on Caucasians. The combined results based on all studies showed that fracture cases had a significantly lower frequency of bb genotype of BsmI [odds ratio (OR) = 0.87, 95% confidence interval (CI)=0.76, 0.98]. When stratifying by fracture type, we found that (1) hip fracture cases had a significantly lower frequency of bb genotype of BsmI (OR=0.82, 95% CI=0.70, 0.97); (2) hip fracture cases had a significantly lower frequency of Tt genotype of TaqI (OR=0.65, 95% CI=0.43, 0.97); (3) hip fracture cases had a significantly higher frequency of tt genotype of TaqI (OR=1.74, 95% CI=1.05, 2.91); (4) vertebral fracture cases had a significantly higher frequency of Aa genotype of ApaI (OR=1.63, 95% CI=1.03, 2.59). No significant difference was found in any genotype of FokI.

CONCLUSION

Our meta-analysis suggests that there is a modest but statistically significant association between the BsmI bb genotypes and fracture.

Relation of bone mineral density to vitamin D receptor gene polymorphism and lifestyle factors in Japanese female workers aged 22-44 years: a cross-sectional study

Bone mineral density (BMD) reflects both genetic and lifestyle factors. The aim of this cross-sectional study was to investigate the influence of vitamin D receptor (VDR) gene polymorphism and lifestyle factors on BMD in premenopausal female workers. The subjects were 162 premenopausal female employees aged 22-44 y who worked at a large-scale integrated manufacturing facility in Japan. BMD was measured at the nondominant radius by dual energy X-ray absorptiometry. Lifestyle information was obtained by a questionnaire at the same time and genomic DNA was isolated from peripheral leukocytes. BMD was positively correlated with age, weight, and body mass index (BMI). The genotype frequencies of VDR gene polymorphism detected by TaqI analysis were 77.2, 22.8, and 0.0% for TT, Tt, and tt, respectively. Analysis of covariance with adjustment for age and BMI showed that the mean BMD was significantly lower in subjects with the Tt genotype than in those with the TT genotype. Subjects who drank alcohol also showed a significantly lower BMD if they had the Tt genotype than if they had the TT genotype. According to multiple linear regression analysis, the independent determinants of BMD were age, BMI, and VDR gene polymorphism. Our data show that BMD is negatively correlated with the Tt genotype of the VDR gene, but positively correlated with age and BMI. These findings suggest that analysis of VDR gene polymorphism may be useful for identifying individuals who are susceptible to osteoporosis so that early preventive measures can be provided.

Evaluation of the effects of vitamin D receptor and estrogen receptor 1 gene polymorphisms on bone mineral density in postmenopausal women

The aim of this study is to evaluate the effects of estrogen receptor 1 (ESR1) and vitamin D receptor (VDR) gene polymorphisms on bone mineral density (BMD) in a group of previously untreated osteoporotic women. Effects of demographic, environmental, and hormonal factors were also evaluated in this context. Fifty women who did not have a prior diagnosis or treatment of osteoporosis were compared with 50 nonosteoporotic postmenopausal women. Demographic and morphometric characteristics, medical history, dietary habits, exercise history, and sunlight exposure were recorded. The diagnosis of osteoporosis was made with regard to BMD measurements with DEXA. Blood samples were obtained for serum biochemistry, bone turnover markers, and VDR and ESR1 gene polymorphism analysis. Polymorphic sites of VDR and ESR1 genes were amplified by polymerase chain reaction and examined using restriction fragment length polymorphism. Bb genotype was significantly higher in the osteoporotic group when compared to controls (p=0.022). Each 1 U decrease in the body mass index (BMI) increased the risk of osteoporosis by 8% independent of the genotype. We could not observe a significant effect of ESR1 polymorphism on BMD or osteoporosis risk. The interaction of ApaI and BsmI genotypes were found to be significant (p=0.041) and the AaBb genotype, when corrected for BMI, was shown to increase the risk of osteoporosis five times (p=0.005). However, the results demonstrated insignificant p values when correction for multiple testing was performed with the Bonferroni method in the logistic regression model. A predominance of Bb genotype of the VDR gene was evident in this group of postmenopausal Turkish women. Moreover, the combined genotype AaBb conferred a five times increased risk for osteoporosis when corrected for clinical variables.

Polymorphism in vitamin D receptor is associated with bone mineral density in patients with adolescent idiopathic scoliosis

Low bone mass and osteopenia have been reported in the axial and peripheral skeleton of adolescent idiopathic scoliosis (AIS) patients. Furthermore, several recent studies have shown that gene polymorphisms are related to osteoporosis. However, no study has yet linked polymorphisms in the vitamin D receptor (VDR) gene and bone mass in AIS. Accordingly, the authors examined the association between bone mass and VDR gene polymorphisms in 198 girls diagnosed with AIS. The VDR BsmI (rs1544410), FokI (rs2228670) and Cdx2 (rs11568820) polymorphisms and bone mineral density at the lumbar spine (LSBMD) and femoral neck (FNBMD) were analyzed and compared to their levels in healthy controls. Mean LSBMD and FNBMD in AIS patients were lower than in age- and sex-matched healthy controls (P = 0.0022 and P = 0.0013, respectively). A comparison of genotype frequencies in AIS patients and controls revealed a significant difference for the BsmI polymorphism only (P = 0.0054). Furthermore, a significant association was found between the VDR BsmI polymorphism and LSBMD. In particular, LSBMD in AIS patients with the AA genotype was found to be significantly lower than in patients with the GA (P < 0.05) or GG (P < 0.01) genotypes. However, no significant association was found between LSBMD or FNBMD and the VDR FokI or Cdx2 polymorphisms. These results suggest that the VDR BsmI polymorphism is associated with LSBMD in girls with AIS.

Pharmacogenetic risk factors for altered bone mineral density and body composition in pediatric acute lymphoblastic leukemia

BACKGROUND

This study investigates pharmacogenetic risk factors for bone mineral (apparent) density (BM(A)D) and body composition in pediatric acute lymphoblastic leukemia

DESIGN AND METHODS

We determined the influence of SNPs in 4 genes (vitamin-D receptor (VDR: BsmI/ApaI/TaqI and Cdx-2/GATA), collagen type I alpha 1 (SpI), estrogen receptor 1 (ESR1: PvuII/XbaI), glucocorticoid receptor (BclI)) on body composition, BM(A)D and fracture risk during dexamethasone-based pediatric acute lymphoblastic leukemia treatment. Body composition and BMD were measured repeatedly during and after treatment using dual energy X-ray absorptiometry.

RESULTS

Non-carriers of VDR 5'-end (Cdx-2/GATA) haplotype 3 revealed a significant larger fat gain than carriers (Delta%fat: non-carriers: +1.76SDS, carriers: +0.77SDS, P<0.001). At diagnosis and during therapy, lumbar spine BMD was significantly higher in non-carriers of VDR 5'-end (Cdx-2/GATA) haplotype 3 than in carriers. The other SNPs did not influence BMD or fracture risk during/after treatment. The year after treatment completion, lean body mass increased in non-carriers of ESR1 (PvuII/XbaI) haplotype 3 and decreased in carriers (Delta lean body mass: non-carriers:+0.28SDS, carriers: -0.55SDS, P<0.01).

CONCLUSIONS

Only VDR 5'-end (Cdx-2/GATA) haplotype 3 was identified as protective factor against excessive fat gain and as a risk factor for lower lumbar spine BMD during treatment. Carrying ESR1 (PvuII/XbaI) haplotype 3 negatively influenced recovery of lean body mass after pediatric acute lymphoblastic leukemia treatment.

Association between bone mineral density and lifestyle factors or vitamin D receptor gene polymorphism in adult male workers: a cross-sectional study

OBJECTIVES

The aim of this cross-sectional study was to investigate the association between bone mineral density (BMD) and lifestyle factors, as well as the influence of vitamin D receptor (VDR) gene polymorphism, in adult male workers.

METHODS

The subjects were 524 male employees aged 23-49 years (37.3 +/- 5.4 years, mean +/- standard deviation) working at a large-scale integrated manufacturing facility in Japan. BMD was measured at the nondominant radius by dual-energy X-ray absorptiometry. Lifestyle information was obtained by a questionnaire at the same time, and genomic DNA was isolated from peripheral leukocytes.

RESULTS

The genotype frequencies of VDR gene polymorphism detected by Taq I digestion were 81.3%, 17.9%, and 0.8% for TT, Tt, and tt, respectively. BMD was 0.56 +/- 0.06 g/cm(2). Analysis of covariance with adjustment for age and body mass index (BMI) revealed that subjects who had a past history of exercise, current exercise from 3 to 7 days a week or daily alcohol intake showed significantly higher BMD than subjects without these features (0.56 +/- 0.06 versus 0.54 +/- 0.06, 0.58 +/- 0.06 versus 0.55 +/- 0.06, and 0.57 +/- 0.06 versus 0.55 +/- 0.06, respectively) (P < 0.05). Subjects who ate only 2 meals a day or smoked >/=21 cigarettes a day showed significantly lower BMD if they had the Tt or tt genotype than if they had the TT genotype (0.51 +/- 0.04 versus 0.56 +/- 0.06 and 0.51 +/- 0.05 versus 0.57 +/- 0.06, respectively) (P < 0.05).

CONCLUSIONS

These findings suggest that the influence of lifestyle on BMD differs according to VDR gene polymorphism in adult male workers.

Update on the pharmacogenetics of the vitamin D receptor and osteoporosis

Vitamin D and calcium are essential for normal skeletal growth and for maintaining the mechanical and structural integrity of the skeleton. Reduced intake of calcium and vitamin D may be associated with reduced bone mass and osteoporosis while a chronic and severe vitamin D deficiency may lead to osteomalacia. Given the importance of vitamin D in bone homeostasis, common polymorphisms in the vitamin D receptor gene were the first to be investigated as possible determinants of bone mass and fracture risk. Even though results are still conflicting and the molecular mechanisms by which these polymorphisms influence receptor activity remain in part to be investigated, an additional important issue is represented by their potential pharmacogenomic and pharmacogenetic implications. This review analyzes major pharmacogenetic studies of polymorphisms in the vitamin D receptor gene and osteoporosis.

Vitamin D receptor gene polymorphism and osteoporosis in the Turkish population

Osteoporosis is one of the most important medical problems facing the aging population. It is defined as a decrease in the bone mass leading to an unacceptably high risk of fractures. Osteoporosis is a multifactorial disease. It is well established that genetic factors are involved in the pathogenesis of osteoporosis. Polymorphism of the vitamin D receptor (VDR) gene has been reported to play a major role in variations for genetic regulation of bone mass. Its role within various ethnic populations is not clear. The purpose of this project was to determine the frequencies of VDR genotypes in Turkey. Three polymorphisms of the VDR gene were analyzed using the polymerase chain reaction-restriction fragment length polymorphism technique. The sample for our study was comprised of postmenopausal women in Turkey, 100 of whom were diagnosed with osteoporosis. They were compared with 146 healthy controls. BsmI genotype frequencies in Turks resemble Caucasians rather than Asians, and Taq genotype frequencies in Turks neither resemble Caucasians nor Asians. The genotype frequencies of VDR were not statistically different between patients with osteoporosis and the control group. Among VDR haplotypes, bbAATT and bbTtAa are more frequent in the osteoporosis group than the control group.

Atherosclerosis and osteoporosis: age-dependent degenerative processes or related entities?

Osteoporosis and atherosclerosis, two multifactorial and degenerative entities, are major public health problems. These diseases accompany the aging process and share common risk factors. Furthermore, several common pathophysiological factors have been suggested. These include similar molecular pathways involving bone and vascular mineralization, estrogen deficiency, parathyroid hormone, homocysteine, lipid oxidation products, inflammatory process, as well as vitamin D and K. Moreover, the use of statins, biphosphonates, beta-blockers and experimental dual-purpose therapies based on the biological linkage of the above entities may simultaneously benefit bone loss and vascular disease. This review considers a potential link between osteoporosis and atherosclerosis beyond aging. These common factors may lead to appropriate treatment strategies.

Genetics of bone loss in rheumatoid arthritis--role of vitamin D receptor polymorphisms

RA is a systemic inflammatory arthritis that leads to local and systemic bone loss. Osteoporosis or the systemic bone loss associated with RA increases the risk for fragility fractures, which can affect quality of life dramatically in RA patients. Although traditional and RA-related risk factors have been defined and studied for osteoporosis associated with RA, genetic factors such as polymorphic variants in the traditional candidate genes for osteoporosis, such as the vitamin D receptor (VDR), type 1 collagen A1 (COLIA1) and oestrogen receptor-alpha (ESR1), have not been well elucidated in RA patients. This review summarizes the currently available literature on the association of VDR polymorphisms with local and systemic bone loss in RA. It also discusses potential targets for genetic research in this area, such as polymorphisms in genes, such as IL-6 (IL6) and TNF receptor type 2 (TNFRSF1B), which control the inflammatory response in RA and may influence bone loss in RA. Defining such genetic factors, in addition to traditional and RA-related risk factors for osteoporosis in RA, may facilitate early identification of patients at high risk for fractures who can then be targeted for treatment.

Pharmacogenetics of osteoporosis and the prospect of individualized prognosis and individualized therapy

PURPOSE OF REVIEW

Description of recent progress in genetics and pharmacogenetics of osteoporosis.

RECENT FINDINGS

Osteoporosis and its consequence of fragility fracture are characterized by highly complex phenotypes, which include bone mineral density, bone strength, bone turnover markers, and nonskeletal traits. Recent developments in the genome-wide studies using high-throughput single-nucleotide polymorphisms have yielded reliable findings. Four genome-wide studies have identified 40 single-nucleotide polymorphisms in various chromosomes that were modestly associated with either bone mineral density or fracture risk. Clinical response, including adverse reactions, to antiosteoporosis therapy (such as bisphosphonates and selective estrogen receptor modulators) is highly variable among treated individuals. Candidate gene studies have found that common polymorphic variations within the collagen I alpha 1 and vitamin D receptor genes were associated with variability in response to antiosteoporosis treatment. Moreover, a recent genome-wide study identified four single-nucleotide polymorphisms that were associated with bisphosphonate-related osteonecrosis of the jaw with relative risk being between 10 and 13.

SUMMARY

The evaluation of osteoporosis and fracture risk is moving from a risk stratification approach to a more individualized approach, in which an individual's absolute risk of fracture is evaluable as a constellation of the individual's environmental exposure and genetic makeup. Therefore, the identification of gene variants that are associated with osteoporosis phenotypes or response to therapy can eventually help individualize the prognosis, treatment and prevention of fracture and its adverse outcomes.

Ethical, legal and social issues of genetic studies with African immigrants as research subjects

There is growing interest in exploring gene-environment interactions in the etiology of diseases in immigrants from sub-Saharan Africa. Our experience working with the Sudanese immigrant population in Omaha, NE, makes clear the pressing need for geneticists and federal and local funding agencies to address the ethical, legal and social implications of genetic research with such vulnerable populations. Our work raises several questions. How does one design research with African immigrant participants to assure it is ethical? Many immigrants may not understand the purposes, risks and benefits involved in research because of low literacy rates, one of the results of civil wars, or concepts of biologic science foreign to their cultures. Is it possible to obtain truly informed consent? Do African immigrants perceive genetic research using them as subjects as racist? Is genetic research on minorities "biopiracy" or "bio-colonialism?" In our experience, some Sudanese immigrants have challenged the legality and ethics of genetic studies with profit-making as an end. We have concluded that it is essential to educate African immigrant or any other non-English-speaking immigrant participants in research using lay language and graphic illustrations before obtaining consent. Cultural proficiency is important in gaining the trust of African immigrants; profit-sharing may encourage their participation in genetic research to benefit all; involvement of African immigrant community leaders in planning, delivery and evaluation using the community-based participatory research approach will facilitate healthcare promotion, health literacy education, as well as genetic research. It is crucial to address the ethical, legal and social implications of genetic studies with African immigrants as research subjects.

Physical work capacity in older adults: implications for the aging worker

BACKGROUND

In many developed countries, the workforce is rapidly aging. Occupational demands however, have not decreased despite the fact that workers see a decline in physical work capacity with age. The purpose of this review is to examine the physiological adaptations to aging, the impact of aging on performance and the benefits of physical fitness in improving functional work capacity in aging individuals.

METHODS

An extensive search of the scientific literature was performed, acquiring published articles which examined the physiological changes associated with age-related decrements in the physical work capacity of healthy aging adults. The databases accessed included AARP Ageline, AccessScience, Annual Reviews, CISTI, Cochrane Library, Clinical Evidence, Digital Dissertations (Proquest), Embase, HealthSTAR, Medline, PubMed, Scopus, and PASCAL and included relevant information sites obtained on the world wide web.

RESULTS

While a great deal of variation exists, an average decline of 20% in physical work capacity has been reported between the ages of 40 and 60 years, due to decreases in aerobic and musculoskeletal capacity. These declines can contribute to decreased work capacity, and consequential increases in work-related injuries and illness. However, differences in habitual physical activity will greatly influence the variability seen in individual physical work capacity and its components. Well-organized, management-supported, work-site health interventions encouraging physical activity during work hours could potentially decrease the incidence of age-related injury and illness.

CONCLUSIONS

Age-associated functional declines and the accompanying risk of work-related injury can be prevented or at least delayed by the practice of regular physical activity. Older workers could optimally pursue their careers until retirement if they continuously maintain their physical training.

Pharmacogenetics of bone treatments: the VDR and ERalpha gene story

Osteoporosis is a common skeletal disease with a strong genetic component characterized by reduced bone mass and increased risk of fragility fractures. Although osteoporosis is a worldwide problem, there are many differences in human ethnics regarding both disease morbidity and drug treatment efficacy. Polymorphisms of vitamin D receptor (VDR) and estrogen receptor-alpha (ERalpha) loci are proposed as genetic determinants of bone quality, skeletal geometry and bone turnover markers. Furthermore, varying responsiveness to vitamin D and estrogen-based treatments may reflect allele variation in their signaling pathway genes (e.g., VDR or ERalpha). Because of their specific ethnic distribution, VDR and ERalpha polymorphisms may be involved in reported human differences of osteoporosis treatment responses.

Genotypes and clinical aspects associated with bone mineral density in Argentine postmenopausal women

The aim of this study was to determine genotypes and clinical aspects associated with bone mineral density (BMD) in postmenopausal women from Córdoba, Argentina. Polymorphisms were assessed by RFLP-PCR technique using BsmI and FokI for vitamin D receptor gene (VDR) and XbaI and PvuII for estrogen receptor-alpha gene (ERalpha) as restrictases. Sixty-eight healthy, 54 osteopenic, and 64 osteoporotic postmenopausal women were recruited. Femoral neck and lumbar spine BMD were inversely correlated with age in the entire analyzed population. Height was lower in osteopenic and osteoporotic women as compared to healthy women (P < 0.05). Weight and body mass index (BMI) were the lowest in osteoporotic women (P < 0.01 versus healthy group). Serum procollagen type I Nterminal propeptide (PINP) was higher in osteoporotic women as compared to the other groups. Distribution of VDR and ERalpha genotypes was similar in the three groups. Genotype bb (VDR) was associated with low values of lumbar BMD in the healthy group (P < 0.05 versus genotype Bb), and with low values of femoral BMD (P < 0.05 versus genotype BB) in osteoporotic women. BB*Pp interaction was associated with the highest femoral neck BMD (P < 0.05), whereas the bb*xx interaction was associated with the lowest femoral neck BMD in the total population analyzed (P < 0.05). In conclusion, parameters such as age, height, weight, BMI, serum PINP, VDR genotypes, and interactions between VDR and ERalpha genotypes could be useful to predict a decrease in BMD in Argentine postmenopausal women.

Osteoporosis, schizophrenia and antipsychotics: the need for a comprehensive multifactorial evaluation

Osteoporosis is recognised as a major public health issue leading to bone fractures, pain and disability. Awareness of an elevated risk of osteoporosis in individuals with schizophrenia is increasing. An accelerated decrease in bone mineral density (BMD) in patients with schizophrenia may be disease related or drug induced. A drug-induced decrease in BMD has been attributed mostly to hyperprolactinaemia and its consequences. However, as demonstrated in this review, decreased BMD and osteoporosis are multifactorial processes, and abnormal bone structure and functions are not limited to BMD. Multiple dynamic processes may lead to impairment of bone homeostasis and eventually to bone abnormalities. Many of these processes may be abnormal in treated as well as untreated patients with schizophrenia. Despite many publications, the epidemiology of abnormal bone structure, mineralisation and dynamics in patients with schizophrenia is still not fully determined. Comprehensive studies of bone dynamics in individuals with first-episode schizophrenia, as well as in patients treated with various current medications, are needed in order to characterise the problem(s) and then to develop relevant treatment and prevention strategies.

Genetics and osteoporosis

Over the past 10 years, many advances have been made in understanding the mechanisms by which genetic factors regulate susceptibility to osteoporosis. It has become clear from studies in man and experimental animals that different genes regulate BMD at different skeletal sites and in men and women. Linkage studies have identified several chromosomal regions that regulate BMD, but only a few causative genes have been discovered so far using this approach. In contrast, significant advances have been made in identifying the genes that cause monogenic bone diseases, and polymorphic variation is some of these genes has been found to contribute to the genetic regulation of BMD in the normal population. Other genes that have been investigated as possible candidates for susceptibility to osteoporosis because of their role in bone biology, such as vitamin D, have yielded mixed results. Many candidate gene association studies have been underpowered, and meta-analysis has been used to try to confirm or refute potential associations and gain a better estimate of their true effect size in the population. Most of the genetic variants that confer susceptibility to osteoporosis remain to be discovered. It is likely that new techniques such as whole-genome association will provide new insights into the genetic determinants of osteoporosis and will help to identify genes of modest effect size. From a clinical standpoint, genetic variants that are found to predispose to osteoporosis will advance our understanding of the pathophysiology of the disease. They could be developed as diagnostic genetic tests or form molecular targets for design of new drugs for the prevention and treatment of osteoporosis and other bone diseases.

Steroid hormone receptor gene polymorphisms and osteoporosis: a pharmacogenomic review

Osteoporosis is a common skeletal disorder with a strong genetic component. In recent years, significant progress has been made in understanding the genetic basis of osteoporosis. Given the biological significance of signalling through steroid hormone receptors, bone biology and calcium homeostasis, alleles of steroid hormone receptor genes have been postulated to contribute to the well-documented genetic predisposition to osteoporosis; and in different studies, these alleles have been associated with variation in bone mass and fracture risk. Even though results are still conflicting and the molecular mechanisms by which these polymorphisms influence receptor activity remain, in part, to be investigated, an additional important issue is represented by potential pharmacogenomic (the investigation of variations of DNA or RNA characteristics as related to drug response) or pharmacogenetic (the influence of variations of DNA sequence on drug response) implications. In fact, steroid hormone receptors actually mediate the action of several compounds known to positively or negatively affect bone homeostasis, such as vitamin D, estrogen and glucocorticoids. This review analyses major pharmacogenetic studies of polymorphisms in steroid hormone receptor genes.

Impact of genetic variation on metabolic response of bone to diet

There is compelling evidence to suggest that both the development of bone to peak bone mass at maturity and subsequent loss depend on the interaction between genetic, hormonal, environmental and nutritional factors. The major part (≤80%) of the age-specific variation in bone turnover and bone density is genetically determined. However, the notion of genetic determinant is of little value unless the specific genes that are involved can be identified. Most work in this area of osteoporosis research has focused on the candidate gene approach, which has identified several candidate genes for osteoporosis, including genes encoding the vitamin D receptor (VDR), oestrogen receptors (α and β), apolipoprotein E, collagen type I α 1 and methylenetetrahydrofolate reductase, amongst many others. However, in general, findings from numerous studies of the association between such genes and various bone variables have been inconsistent. In addition to possible gene—gene interactions it is likely that there are interactions between these genes and certain environmental factors, especially nutrition, that may mediate expression of bone-related phenotypes. While these potential interactions add a level of complexity to our understanding of these apparent genetic effects on bone, identification of a role for genetic factors without knowledge of their interaction with nutrients can do little to advance prevention and treatment of osteoporosis. This information is especially important because, unlike genotype, diet and nutrition can be modified. The aim of the present review is to critically evaluate current knowledge relating to candidate genes for osteoporosis, with particular emphasis on their interaction with nutrients and dietary factors in determining bone health.

Caffeine decreases vitamin D receptor protein expression and 1,25(OH)2D3 stimulated alkaline phosphatase activity in human osteoblast cells

Of the various risk factors contributing to osteoporosis, dietary/lifestyle factors are important. In a clinical study we reported that women with caffeine intakes >300 mg/day had higher bone loss and women with vitamin D receptor (VDR) variant, tt were at a greater risk for this deleterious effect of caffeine. However, the mechanism of how caffeine effects bone metabolism is not clear. 1,25-Dihydroxy vitamin D(3) (1,25(OH)(2)D(3)) plays a critical role in regulating bone metabolism. The receptor for 1,25(OH)(2)D(3), VDR has been demonstrated in osteoblast cells and it belongs to the superfamily of nuclear hormone receptors. To understand the molecular mechanism of the role of caffeine in relation to bone, we tested the effect of caffeine on VDR expression and 1,25(OH)(2)D(3) mediated actions in bone. We therefore examined the effect of different doses of caffeine (0.2, 0.5, 1.0 and 10mM) on 1,25(OH)(2)D(3) induced VDR protein expression in human osteoblast cells. We also tested the effect of different doses of caffeine on 1,25(OH)(2)D(3) induced alkaline phosphatase (ALP) activity, a widely used marker of osteoblastic activity. Caffeine dose dependently decreased the 1,25(OH)(2)D(3) induced VDR expression and at concentrations of 1 and 10mM, VDR expression was decreased by about 50-70%, respectively. In addition, the 1,25(OH)(2)D(3) induced alkaline phosphatase activity was also reduced at similar doses thus affecting the osteoblastic function. The basal ALP activity was not affected with increasing doses of caffeine. Overall, our results suggest that caffeine affects 1,25(OH)(2)D(3) stimulated VDR protein expression and 1,25(OH)(2)D(3) mediated actions in human osteoblast cells.

FokI polymorphism of the vitamin D receptor gene correlates with parameters of bone mass and turnover in a female population of the Italian island of Lampedusa

One of the most promising genetic approaches to dissecting a multifactorial disease is represented by genetically isolated population studies. We studied a genetic marker in a cohort of women living on the Mediterranean island of Lampedusa, a geographically isolated population. Lampedusa, located between the African coast and Sicily, consists of a young genetic isolate (<20 generations) with an exponential growth in the last generations. We analyzed the association between the FokI vitamin D receptor (VDR) gene polymorphism, previously proposed as a predictor of bone mass, with parameters of bone mass and turnover in a cohort of pre- and postmenopausal women living on Lampedusa. In 424 women (277 postmenopausal and 147 premenopausal), allelic frequencies were 49% for the F allele and 51% for the f allele. Using analysis of covariance, we found that subjects with ff genotype exhibited a significantly (P < 0.001) lower lumbar spine bone mass, by dual-energy X-ray absorptiometry, and lower values of bone ultrasonographic parameters (speed of sound and broadband ultrasound attenuation) relative to those with Ff and FF genotypes. Conversely, osteocalcin and serum cross-laps were significantly higher in ff and Ff compared to FF genotype. Our data suggest that FokI VDR polymorphism may contribute to the determination of bone mass and turnover in both pre- and postmenopausal women in this geographically isolated population.

Evolution and translation of research findings: from bench to where?

The credibility and replication of research findings evolve over time, as data accumulate. However, translation of postulated research promises to real-life biomedical applications is uncommon. In some fields of research, we may observe diminishing effects for the strength of research findings and rapid alternations of exaggerated claims and extreme contradictions--the "Proteus Phenomenon." While these phenomena are probably more prominent in the basic sciences, similar manifestations have been documented even in clinical trials and they may undermine the credibility of clinical research. Significance-chasing bias may be in part responsible, but the greatest threat may come from the poor relevance and scientific rationale and thus low pre-study odds of success of research efforts. Given that we currently have too many research findings, often with low credibility, replication and rigorous evaluation become as important as or even more important than discovery. Credibility, replication, and translation are all desirable properties of research findings, but are only modestly correlated. In this essay, I discuss some of the evidence (or lack thereof) for the process of evolution and translation of research findings, with emphasis on the biomedical sciences.

Vitamin D receptor gene BsmI and TaqI polymorphisms and fracture risk: a meta-analysis

INTRODUCTION

Fracture is the major clinical outcome of osteoporosis. The vitamin D receptor (VDR) gene is thought to be a candidate gene for osteoporosis. Many genetic studies have suggested an association of VDR polymorphisms and osteoporosis, but evidence remains conflicting.

MATERIALS AND METHODS

We searched published studies from 1996 to September 2005 through PubMed and evaluated the genetic effect of the BsmI and TaqI polymorphism of VDR on fracture risk in a meta-analysis. Thirteen studies with a total of 20 eligible comparisons (1632 fracture cases and 5203 controls) were analyzed with fixed and random effects models.

RESULT

No evidence of relationship between the VDR BsmI or TaqI polymorphism and fracture risk was observed with any genetic model. The odds ratio (95% confidence interval) of b-allele versus B-allele was 0.98 (0.86-1.12) with random effects calculations. There was significant between-study heterogeneity. Small studies did not differ significantly from larger ones.

CONCLUSION

No relationship of the VDR BsmI or TaqI polymorphism and fracture risk was found in the meta-analysis of published data.

Vitamin D receptor polymorphisms and diseases

The vitamin D endocrine system is central to the control of bone and calcium homeostasis. Thus, alterations in the vitamin D pathway lead to disturbances in mineral metabolism. Furthermore, a role for vitamin D has been suggested in other diseases, like cancer, diabetes and cardiovascular disease. Expression and nuclear activation of the vitamin D receptor (VDR) are necessary for the effects of vitamin D. Several genetic variations have been identified in the VDR. DNA sequence variations, which occur frequently in the population, are referred to as "polymorphisms" and can have biological effects. To test whether there is a linkage between VDR polymorphisms and diseases, epidemiological studies are performed. In these studies, the presence of a variation of the gene is studied in a population of patients, and then compared to a control group. Thus, association studies are performed, and a link among gene polymorphisms and diseases can be established. Since the discovery of VDR polymorphisms a number of papers have been published studying its role in bone biology, renal diseases, diabetes, etc. The purpose of this review is to summarize the vast amount of information regarding vitamin D receptor polymorphisms and human diseases, and discuss its possible role as diagnostic tools.

Genetics of osteoporosis

Osteoporosis is a common disease with a strong genetic component. In recent years, some progress has been made in understanding the genetic basis of osteoporosis. Genetic factors contribute to osteoporosis by influencing not only bone mineral density but also bone size, bone quality, and bone turnover. Meta-analysis has been used to define the role of several candidate genes in osteoporosis. Some quantitative trait loci that regulate bone mass identified by linkage studies in humans and experimental animals have been replicated in multiple populations. Genes that cause monogenic bone diseases also contribute to regulation of bone mass in the normal population. Genome-wide association studies and functional genomics approaches have recently begun to apply to genetic studies of osteoporosis. In the future, not only single gene but also the entire gene networks involved in osteoporosis and regulation of bone mass will systematically be discovered through integrative genomics.

Correlation of estrogen receptor beta gene polymorphisms with spinal bone mineral density in peri- and post-menopausal Greek women

Estrogens play a significant role in bone physiology. Their action is mainly exerted through their receptors. Estrogen receptor alpha (ERalpha) plays a major role in bone homeostasis and there is evidence suggesting that estrogen receptor beta (ERbeta) has also an effect on BMD. We investigated the possible effect of two ERbeta gene polymorphisms on spinal bone mineral density (BMD) and metabolic bone markers in Greek women. Spine BMD as well as biochemical bone markers were measured in 147 healthy peri- and post-menopausal women [mean age (S.D.) 54 (7.9) years]. Genotyping was performed for two restriction fragment length polymorphisms (RFLPs) of ERbeta gene, RsaI in exon 5 and AluI in exon 8. For each polymorphism studied the cohort was divided into two groups: the "wild-type" group (RR and AA, respectively) and the "carrier" group including subjects with at least one allele with the restriction site (Rr&rr and Aa&aa, respectively). The distribution of RsaI genotypes was RR: 91.2% (n = 134), Rr: 8.2% (n = 12), and rr: 0.6% (n = 1) and of AluI genotypes AA: 36.7% (n = 54), Aa: 57.2% (n = 84), and aa: 6.1% (n = 9). No linkage disequilibrium was found between the two polymorphic sites studied. Spine BMD did not differ significantly in the two groups of either polymorphism, after adjusting for age, weight, height, and years since menopause [mean BMD (S.D.) for RR 0.841 (0.17) g/cm(2) versus Rr&rr 0.798 (0.13) g/cm(2), p = 0.25, and mean BMD (S.D.) for AA 0.828 (0.16)g/cm(2) versus Aa&aa 0.848 (0.17) g/cm(2), p = 0.32]. No significant differences were noted in metabolic bone markers except for a marginal difference of RR versus Rr/rr in urinary hydroxyproline/creatinine ratio [median (IQR) 3.88 (6.04) micromol/mmol in RR versus 8.2 (4.32) micromol/mmol in Rr/rr, p = 0.05]. Furthermore, no interaction between the two polymorphisms on BMD was found. In conclusion, in a Greek female post-menopausal population, the two ERbeta gene polymorphisms were not associated with BMD, or metabolic bone markers.