Genetic polymorphisms of OPG, RANK, and ESR1 and bone mineral density in Korean postmenopausal women

Osteoprotegerin Gene as a Biomarker in the Development of Osteoporosis in Postmenopausal Women

Osteoporosis is a multifactorial and polygenic disease caused by an imbalance between osteoclastogenesis and osteoblastogenesis, leading to a decrease in bone mineral density and the occurrence of disorders in the microarchitecture and metabolism of bone tissue. In postmenopausal women, there is a significant decrease in the production of estrogens, which play a key role in maintaining proper bone mineral density. Estrogens have an inhibitory effect on the development and activity of osteoclasts by reducing the synthesis of pro-resorption cytokines and stimulating the expression of osteoprotegerin (OPG). Osteoprotegerin is a cytokine that prevents bone loss by inhibiting the process of osteoclastogenesis, reducing bone resorption. The aim of our study was to determine the influence of the rs3102735 (-163A>G), rs3134070 (-245T>G), rs207361 (-950T>C), rs7844539 (6890A>C), and rs2073618 (1181G>C) polymorphisms of the OPG gene on the risk of osteoporosis and osteopenia in postmenopausal Polish women. The study included 802 unrelated women (osteoporosis: n = 317, osteopenia: n = 110, controls: n = 375) at postmenopausal age (54.7 ± 8.6 years). Genetic analysis was performed using real-time PCR. BMD values as well as clinical and bone parameters with the tested polymorphisms were analyzed among the study population. Analysis of the PPARG rs1801282 variants did not show any association with the risk of osteoporosis and osteopenia. However, for the OPG rs207361 polymorphism, we observed a statistically significant association with the risk of osteoporosis, suggesting that the OPG rs207361 variant may be one of the genetic markers associated with the pathogenesis of osteoporosis.

Predictors of decreased bone mineral density in childhood systemic lupus erythematosus: possible role of osteoprotegerin gene polymorphisms

OBJECTIVES

This study aims to explore effects of osteoprotegerin (OPG) gene polymorphisms and other possible factors on bone mineral density (BMD) in children with systemic lupus erythematosus (SLE).

METHODS

Osteoprotegerin gene rs2073617 and rs3134069 were evaluated in 74 SLE patients and 100 controls then genotypes, alleles and haplotypes' frequencies were compared between cases and controls and between patients with BMD z-scores above and below -2 evaluated by dual energy X-ray absorptiometry (DEXA). Disease activity was evaluated by SLE disease activity index (SLEDAI).

RESULTS

The patients aged 14.01 ± 2.6 years and included 57 (77%) females and 27 (36%) patients with BMD z-score below -2. Genotypes, alleles, and haplotypes frequencies did not differ between patients and controls (p>0.05 for all). Rs3134069 GG genotype and G allele (p=0.001, 0.002) and rs2073617 TT genotype and T allele (p=0.01, 0.006) were significantly higher in patients with BMD below -2. Cumulative glucocorticoids dose, disease duration, and SLEDAI scores were higher in patients with BMD below -2 (p=0.01, 0.01, <0.001, respectively). Regression analysis showed T allele of rs2073617, duration of illness (above 36 months), and cumulative SLEDAI (above 10) as independent predictors of decreased BMD (p 0.02, 0.003, and 0.002, respectively).

CONCLUSIONS

This is the first study to demonstrate OPG gene influence on BMD in children with SLE. The studied SNPs are not risk for developing SLE but, rs2073617 T allele is a possible predictor for reduced BMD in SLE. Other predictors include long disease duration and high activity supporting that osteoporosis in SLE is multifactorial.

Integrative analysis of genetic and clinical risk factors for bone loss in a Korean population

PURPOSE

The relative contribution of genetic and clinical factors for bone loss is not well known. This study aimed to investigate the annualized percentage change in total hip bone mineral density (BMD) and the genetic and clinical risk factors for bone loss in a Korean prospective cohort study over a 6-year period.

METHODS

We included 645 men aged ≥50 years and 683 postmenopausal women who had repeated BMD testing between 2007 and 2014. The association between covariates and annualized percentage change in hip BMD was analyzed through the multivariate linear regression analysis. A total of 2614 single-nucleotide polymorphisms (SNPs) from 23 known BMD-related candidate genes and genome-wise association study were investigated.

RESULTS

Hip bone loss increased more rapidly in women than in men with advancing age. Hip bone loss in men increased with lean mass (LM) loss (%/year) (P < 0.001) and current smoking (P = 0.024) and decreased with increasing waist circumference (WC) (P < 0.001), alcohol consumption (P = 0.049), and increase in red blood cell counts (P = 0.031). Decreasing WC (P = 0.009), LM loss (%/year) (P < 0.001), and years since menopause ≤ 3 years (P = 0.003) significantly correlated with hip bone loss in women aged 45-59 years. Hip bone loss in women aged ≥60 years increased with advancing age (P = 0.012), alcohol consumption (P = 0.028), LM loss (%/year) (P = 0.031), and fat mass loss (%/year) (P < 0.001) and decreased with increasing WC (P = 0.025). LRP5 rs498830 (β = 0.127, P = 0.007) and TNFSF11 rs7325635 (β = 0.146, P = 0.001) were the top SNPs related to hip bone loss in men and postmenopausal women, respectively. However, none of the SNPs were associated with hip bone loss after Benjamini-Hochberg adjustment.

CONCLUSION

In this study, decreasing WC and LM were significant risk factors for hip bone loss in both men and women. Those factors were also identified that had sex-specific or age-specific effects on hip bone loss. None of the SNPs were associated with hip bone loss after multiple testing adjustments. The understanding of the modifiable factors contributing to bone loss has been broadened, and this may have implications such as in developing individualized preventive strategy. Further studies are needed to better predict the risk for bone loss in men and women.

Genetic Impact on Bone Modulation-A Review Bridging Bioscience to Genetic Engineering

Genes control approximately 60% to 75% of the variance of peak bone mass/density and a much smaller amount of variance in rate of loss.

Bone mass increases during growth to a peak value and soon after begins to decline. Most of the genetic effect is exerted during growth and so influences peak bone mass; whether there is an additional genetic effect on the rate of bone loss is less clear. So, this article aims to place emphasis on various oral and systemic conditions that are manifested due to altered gene function. Genetic polymorphisms and mutations are simple, although the consequences of the mechanism are complex. The syndromic manifestation due to changes at genetic level will greatly affect the bone quality, which will ultimately affect any treatment prognosis. Hence, a better understanding of molecular mechanisms of bone remodeling helps to identify pathogenic causes of bone, skeletal diseases, and leads to the development of targeted therapies for these diseases. This review highlights notions on the connecting link between science and genetics as well as various oral scenarios where gene could bring about changes, resulting in deformities. There is an intense research awaited in the future which could intervene with the causes that bring about genetic modulations, so as to decrease the mortality rate of humans.

The genetic association between osteoprotegerin (OPG) gene polymorphisms and bone mineral density (BMD) in postmenopausal women: A meta-analysis

BACKGROUND

Osteoporosis is a common skeletal disorder in eldest people, especially in postmenopausal women. The osteoprotegerin (OPG) gene has been reported to be associated with the BMD and pathogenesis of osteoporosis. However, the results were inconsistent and inconclusive in previous studies.

METHODS

A meta-analysis was performed to investigate the effect of four common OPG gene polymorphisms (A163G, G1181C, T245G, and T950C) on BMD in postmenopausal women.

RESULTS

A total of 23 eligible studies with 12,973 postmenopausal women were enrolled in present study. Individuals who with AA genotype of A163G were found to have slightly higher femoral hip (P = .03, SMD = 0.49, [95% CI] = [0.06, 0.91]) and total hip BMD (P = .002, SMD = -0.25, [95% CI] = [-0.42, -0.09]) than those with AG genotype. Subjects with GG genotype of G1181C was found to have lower BMD than those with CC or GC genotypes in lumbar spine (GG vs GC: P = .0002, SMD = -0.85, [95% CI] = [-1.29, -0.41]; GG vs CC: P = .02, SMD = -0.21, [-0.39, -0.03]) and total hip BMD (GG vs GC: P = .002, SMD = -0.25, [95% CI] = [-0.42, -0.09]; GG vs CC: P = .01, SMD = -0.15, [95% CI] = [-0.26, -0.03]). In addition, the subjects with GC genotype of G1181C was detected to have lower BMD than those with CC genotype in lumbar spine BMD (P < .05). Furthermore, individuals with TT genotype of T950C were shown to have significant lower lumbar spine BMD compared with those with genotype CC in Caucasian (P < .05). The lumbar spine BMD was lower for subjects with TC genotype of T950C than those with CC genotype in both Caucasian and Asian populations (P < .05). In contrast to A163G, G1181C, and T950G, no association was detected between T245G polymorphism and BMD (P > .05).

CONCLUSION

The present meta-analysis demonstrated the OPG A163G, G1181C, and T950G, but not T245G, might influence the BMD in postmenopausal women.

Polymorphism rs2073618 of the TNFRSF11B (OPG) Gene and Bone Mineral Density in Mexican Women with Rheumatoid Arthritis

Osteoporosis (OP) is highly prevalent in rheumatoid arthritis (RA) and is influenced by genetic factors. Single-nucleotide polymorphism (SNP) rs2073618 in the TNFRSF11B osteoprotegerin (OPG) gene has been related to postmenopausal OP although, to date, no information has been described concerning whether this polymorphism is implied in abnormalities of bone mineral density (BMD) in RA. We evaluated, in a case-control study performed in Mexican-Mestizo women with RA, whether SNP rs2073618 in the TNFRSF11B gene is associated with a decrease in BMD. RA patients were classified as follows: (1) low BMD and (2) normal BMD. All patients were genotyped for the rs2073618 polymorphism by PCR-RFLP. The frequency of low BMD was 74.4%. Higher age was observed in RA with low BMD versus normal BMD (62 and 54 years, resp.; p < 0.001). Worse functioning and lower BMI were observed in RA with low BMD (p = 0.003 and p = 0.002, resp.). We found similar genotype frequencies in RA with low BMD versus RA with normal BMD (GG genotype 71% versus 64.4%, GC 26% versus 33%, and CC 3% versus 2.2%, resp.; p = 0.6). We concluded that in Mexican-Mestizo female patients with RA, the rs2073618 polymorphism of the TNRFS11B gene is not associated with low BMD.

Prevalence of polymorphisms in OPG, RANKL and RANK as potential markers for Charcot arthropathy development

Charcot arthropathy is one of the most serious complications of diabetic foot syndrome that leads to amputation of the affected limb. Since there is no cure for Charcot arthropathy, early diagnosis and implementation preventive care are the best available treatment. However, diagnosis is hindered by obscure clinical picture of the disease and lack of molecular markers for its early detection. Results of recent research suggest that OPG-RANKL-RANK axis regulating bone metabolism can be associated with Charcot arthropathy and that SNPs in OPG gene are associated with the disease. Here we report the results of comprehensive analysis of ten SNPs in OPG, RANKL and RANK genes in 260 subjects divided into diabetes, neuropathy and Charcot arthropathy groups. Besides genotype analysis we performed linkage disequilibrium and hierarchical clustering to obtain information about correlation between SNPs. Our results show that OPG 245T/G (rs3134069) and OPG 1217C/T (rs3102734) polymorphisms co-occur in patients with Charcot arthropathy (r2 = 0.99). Moreover, hierarchical clustering revealed a characteristic profile of all SNPs in Charcot arthropathy and neuropathy, which is distinct from control group. Our results suggest that analysis of multiple SNPs can be used as potential marker of Charcot arthropathy and provide insight into possible molecular mechanisms of its development.

Associations between OPG and RANKL polymorphisms, vertebral fractures, and abdominal aortic calcification in community-dwelling older subjects: the Sao Paulo Ageing & Health Study (SPAH)

This is the first study analyzing concomitantly osteoprotegerin (OPG)/receptor activator of nuclear factor kappa B ligand (RANKL) polymorphisms and OPG/RANKL serum levels and their association with bone mineral density (BMD), vertebral fractures, and vascular aortic calcification in a cohort of 800 subjects in community-dwelling older individuals.

INTRODUCTION

Osteoprotegerin (OPG) and RANKL play an important role in osteoclast activation and differentiation as well as in vascular calcification. At present, there are no studies of OPG or RANKL gene polymorphisms in Brazilian older populations. The aim of this study was to evaluate OPG/RANKL polymorphism and their association with vertebral fractures (VFs) and aortic calcification.

METHODS

Eight hundred subjects (497 women/303 men) were genotyped for the OPG 1181G>C (rs2073618), 163C>T (rs3102735), 245T>G (rs3134069), and 209G>A (rs3134070) and RANKL A>G (rs2277438) single-nucleotide polymorphisms (SNPs). VFs were evaluated by spine radiography (Genant's method). Aortic calcification was quantified using Kauppila's method.

RESULTS

The isolated genotype analyses and single-allele frequency data showed association of OPG 163C, 245G, and 209A alleles with presence of VFs (P < 0.05). Multiple logistic regression of subjects with absence of VFs vs. those with VFs (grades II/III) revealed only OPG 209A homozygosity as a risk factor for higher-grade VFs (odds ratio (OR) = 4.17, 95 % CI 1.03-16.93, P = 0.046). Regarding aortic calcification, the isolated genotype analysis frequency data revealed a significant association of OPG 1181G, 163C, 245G, and 209A alleles with absent aortic calcification (P < 0.05). Multiple logistic regression data confirmed that the OPG 209A allele was protective for aortic calcification (OR = 0.63, 95 % CI 0.45-0.88, P = 0.007) and the OPG 1181C allele was a risk factor for aortic calcification (OR = 1.26, 95 % CI 1.00-1.58, P = 0.046).

CONCLUSION

This study showed that the OPG 209AA genotype was a risk factor for higher-grade VFs, the OPG 209A allele was protective for aortic calcification, and the OPG 1181C was a risk factor for aortic calcification, supporting the involvement of OPG polymorphisms in the analyzed phenotypes and the concept that the related pathogenesis is multifactorial.

Genetic control of bone mass

Bone mineral density (BMD) is a quantitative traits used as a surrogate phenotype for the diagnosis of osteoporosis, a common metabolic disorder characterized by increased fracture risk as a result of a decreased bone mass and deterioration of the microarchitecture of the bone. Normal variation in BMD is determined by both environmental and genetic factors. According to heritability studies, 50-85% of the variance in BMD is controlled by genetic factors which are mostly polygenic. In contrast to the complex etiology of osteoporosis, there are disorders with deviating BMD values caused by one mutation with a large impact. These mutations can result in monogenic bone disorders with either an extreme high (sclerosteosis, Van Buchem disease, osteopetrosis, high bone mass phenotype) or low BMD (osteogenesis imperfecta, juvenile osteoporosis, primary osteoporosis). Identification of the disease causing genes, increased the knowledge on the regulation of BMD and highlighted important signaling pathways and novel therapeutic targets such as sclerostin, RANKL and cathepsin K. Genetic variation in genes involved in these pathways are often also involved in the regulation of normal variation in BMD and osteoporosis susceptibility. In the last decades, identification of genetic factors regulating BMD has proven to be a challenge. Several approaches have been tested such as linkage studies and candidate and genome wide association studies. Although, throughout the years, technological developments made it possible to study increasing numbers of genetic variants in populations with increasing sample sizes at the same time, only a small fraction of the genetic impact can yet be explained. In order to elucidate the missing heritability, the focus shifted to studying the role of rare variants, copy number variations and epigenetic influences. This review summarizes the genetic cause of different monogenic bone disorders with deviating BMD and the knowledge on genetic factors explaining normal variation in BMD and osteoporosis risk.

Osteoporosis and polymorphisms of osteoprotegerin gene in postmenopausal women - a pilot study

Objectives

Osteoprotegerin (OPG) has an important role in bone remodeling, and it has been proposed that the OPG gene might be a candidate gene for osteoporosis predisposition. Several studies have already assessed the connection between OPG gene polymorphism and bone mineral density (BMD). In this study we wanted to analyze the association of two polymorphisms in the OPG gene with BMD and bone turnover markers in women with and without osteoporosis.

Material and methods

In 22 postmenopausal women with osteoporosis (aged 65.6 ±12.6) and 59 women without osteoporosis (aged 60.8 ±8.7) we analyzed the association of two polymorphisms in the OPG gene with BMD, measured by dual energy absorptiometry and with bone turnover markers (crosslaps and osteoprotegerin). A163G, G209A, T245G and G1181C polymorphisms were determined.

Results

No significant differences in age, anthropometry, number of fractures, osteocalcin and cross-laps were found between women with and without osteoporosis. Women with osteoporosis were significantly longer in postmenopause. Significantly more women with osteoporosis had AG polymorphism (p = 0.038) compared to women without osteoporosis, while no significant difference was found in prevalence of TT and GG polymorphism between patients with and without osteoporosis. No relationship was found between investigated polymorphism and bone turnover markers. A significant negative correlation between total hip BMD and crosslaps (p = 0.046) as well as between total hip T score and crosslaps (p = 0.044) was found in women without osteoporosis

Conclusions

Postmenopausal women with osteoporosis had AG polymorphism more frequently than women without osteoporosis. Our results indicate that A163G polymorphism could have an impact on higher bone loss in postmenopausal women.

Polymorphisms in genes in the RANKL/RANK/OPG pathway are associated with bone mineral density at different skeletal sites in post-menopausal women

Association between 22 single nucleotide polymorphisms (SNPs) in the TNFSF11, TNFRSF11A, and TNFRSF11B genes in the RANKL/RANK/OPG pathway with bone mineral density (BMD) in 881 post-menopausal women. Our results suggest that TNFSF11 and TNFRSF11A, but not TNFRSF11B, genetic polymorphisms influence BMD mainly in the femoral neck in post-menopausal Chinese women.

INTRODUCTION

The aim of this study was to assess the relationship of polymorphisms in the TNFSF11, TNFRSF11A, and TNFRSF11B genes in the RANKL/RANK/OPG pathway with bone mineral density (BMD) in a cohort of Chinese post-menopausal women.

METHODS

A cross-sectional study was conducted in 881 post-menopausal women aged 50-89 years. All participants underwent lumbar spinal (LS) and femoral neck (FN) BMD evaluation by dual-energy X-ray absorptiometry. Twenty-two TNFSF11, TNFRSF11A, and TNFRSF11B SNPs were genotyped. We tested whether a single SNP or a haplotype was associated with BMD variations.

RESULTS

Two SNPs in the TNFSF11 gene (rs2277439 and rs2324851) and one in the TNFRSF11A gene (rs7239261) were found to be significantly associated with FN BMD (p = 0.014, 0.013, and 0.047, respectively). Haplotype TGACGT of TNFSF11 rs9525641-rs2277439-rs2324851-rs2875459-rs2200287-rs9533166 was a genetic risk factor toward a lower FN BMD (beta = -0.1473; p = 0.01126). In contrary, haplotype TAGCGT of TNFSF11 rs9525641-rs2277439-rs2324851-rs2875459-rs2200287-rs9533166 was genetic protective factor for LS BMD (beta = 0.3923; p = 0.04917).

CONCLUSIONS

Our findings suggest that TNFSF11 and TNFRSF11A, but not TNFRSF11B, genetic polymorphisms influence BMD mainly in the femoral neck in post-menopausal Chinese women. This contributes to the understanding of the role of genetic variation in this pathway in determining bone health.

Association of osteoporosis susceptibility genes with bone mineral density and bone metabolism related markers in Koreans: the Chungju Metabolic Disease Cohort (CMC) study

In this study, we evaluated the association between bone mineral density (BMD) and 10 single-nucleotide polymorphisms (SNPs) within eight osteoporosis susceptibility genes that were previously identified in genome-wide association studies (GWASs). A total of 494 men and 493 postmenopausal women participating in the Chungju Metabolic Disease cohort study in Korea were included. The following 10 SNPs were genotyped: ZBTB40 rs6426749, MEF2C rs1366594, ESR1 rs2941740, TNFRSF11B rs3134070, TNFRSF11B rs2073617, SOX6 rs711785, LRP5 rs599083, TNFSF11 rs227438, TNFSF11 rs9594782, and FOXL1 rs10048146; and the association between these SNPs and bone metabolism-related markers was assessed. Two SNPs, TNFSF11 rs2277438 and FOXL1 rs1004816, were associated with lumbar spine BMD. TNFSF11 rs2277438 in men and SOX6 rs7117858 and FOXL1 rs10048146 in postmenopausal women were found to be associated with lumbar BMD. ZBTB40 rs6426749, MEF2C rs1366594, and LRP5 rs599083 showed significant associations with femur neck BMD. These three SNPs in men and MEF2C rs1366594 and ESR1 rs2941740 in postmenopausal women were associated with femur neck BMD. A significant association between MEF2C rs1366594 and serum calcium levels was observed in men. Serum phosphorus levels were related to SOX6 rs7117858. Serum PTH levels were significantly associated with TNFRSF11B rs3134070 in men, and SOX6 rs711858 in postmenopausal women. In conclusion, our study independently confirmed associations between several SNPs: ZBTB40, MEF2C, ESR1, SOX6, LRP5, TNFSF11, and FOXL1 and bone marrow density in the Korean population.

Osteoporosis risk prediction for bone mineral density assessment of postmenopausal women using machine learning

PURPOSE

A number of clinical decision tools for osteoporosis risk assessment have been developed to select postmenopausal women for the measurement of bone mineral density. We developed and validated machine learning models with the aim of more accurately identifying the risk of osteoporosis in postmenopausal women compared to the ability of conventional clinical decision tools.

MATERIALS AND METHODS

We collected medical records from Korean postmenopausal women based on the Korea National Health and Nutrition Examination Surveys. The training data set was used to construct models based on popular machine learning algorithms such as support vector machines (SVM), random forests, artificial neural networks (ANN), and logistic regression (LR) based on simple surveys. The machine learning models were compared to four conventional clinical decision tools: osteoporosis self-assessment tool (OST), osteoporosis risk assessment instrument (ORAI), simple calculated osteoporosis risk estimation (SCORE), and osteoporosis index of risk (OSIRIS).

RESULTS

SVM had significantly better area under the curve (AUC) of the receiver operating characteristic than ANN, LR, OST, ORAI, SCORE, and OSIRIS for the training set. SVM predicted osteoporosis risk with an AUC of 0.827, accuracy of 76.7%, sensitivity of 77.8%, and specificity of 76.0% at total hip, femoral neck, or lumbar spine for the testing set. The significant factors selected by SVM were age, height, weight, body mass index, duration of menopause, duration of breast feeding, estrogen therapy, hyperlipidemia, hypertension, osteoarthritis, and diabetes mellitus.

CONCLUSION

Considering various predictors associated with low bone density, the machine learning methods may be effective tools for identifying postmenopausal women at high risk for osteoporosis.

Gene-gene interaction between RBMS3 and ZNF516 influences bone mineral density

Osteoporosis is characterized by low bone mineral density (BMD), a highly heritable trait that is determined, in part, by the actions and interactions of multiple genes. Although an increasing number of genes have been identified to have independent effects on BMD, few studies have been performed to identify genes that interact with one another to affect BMD. In this study, we performed gene-gene interaction analyses in selected candidate genes in individuals with extremely high versus low hip BMD (20% tails of the distributions), in two independent U.S. Caucasian samples. The first sample contained 916 unrelated subjects with extreme hip BMD Z-scores selected from a population composed of 2286 subjects. The second sample consisted of 400 unrelated subjects with extreme hip BMD Z-scores selected from a population composed of 1000 subjects. Combining results from these two samples, we found one interacting gene pair (RBMS3 versus ZNF516) which, even after Bonferroni correction for multiple testing, showed consistently significant effects on hip BMD. RMBS3 harbored two single-nucleotide polymorphisms (SNPs), rs6549904 and rs7640046, both of which had significant interactions with an SNP, rs4891159, located on ZNF516 (p = 7.04 × 10(-11) and 1.03 × 10(-10) ). We further validated these results in two additional samples of Caucasian and African descent. The gene pair, RBMS3 versus ZNF516, was successfully replicated in the Caucasian sample (p = 8.07 × 10(-3) and 2.91 × 10(-3) ). For the African sample, a significant interaction was also detected (p = 0.031 and 0.043), but the direction of the effect was opposite to that observed in the three Caucasian samples. By providing evidence for genetic interactions underlying BMD, this study further delineates the genetic architecture of osteoporosis.

Association of genetic polymorphisms of RANK, RANKL and OPG with bone mineral density in Chinese peri- and postmenopausal women

OBJECTIVES

To explore the influence of 14 single nucleotide polymorphisms (SNPs) in receptor activator of nuclear factor-kappa B (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) on bone mineral density (BMD) in a Chinese female population.

DESIGN AND METHODS

A cross-sectional study was conducted in 108 perimenopausal and 127 postmenopausal women aged 43-65 years. All participants underwent lumbar spinal and nondominant femoral BMD evaluation by dual energy X-ray absorptiometry. Fourteen RANK, RANKL and OPG genotypes were determined by chip-based MALDI-TOF mass spectrometry. The differences between the BMDs of the RANK genotypes were analyzed.

RESULTS

Five SNPs (rs6993813, rs4355801, rs1032129 and rs2073618 in OPG and rs3018362 in RANK) were significantly associated with BMD or with BMD adjusted for body weight or years since menopause, mostly at the femoral neck but also partly at the total hip (p<0.05). The risk allele frequencies observed in our sample were different from those found in Europeans but the effects of these risk alleles on BMD values had the same direction in our cohort as in Europeans, except for rs3018362 with G as the risk allele, which was contrary to other studies. None of the SNPs in RANKL were associated with BMD at any anatomical site.

CONCLUSIONS

Our findings suggest that OPG and RANK but not RANKL genetic polymorphisms influence BMD mainly in the femoral neck in peri- and postmenopausal Chinese women. This contributes to the understanding of the role of genetic variation in this pathway in determining bone health.

Genetic polymorphism of the OPG gene associated with breast cancer

Background

The receptor activator of NF-κB (RANK), its ligand (RANKL) and osteoprotegerin (OPG) have been reported to play a role in the pathophysiological bone turnover and in the pathogenesis of breast cancer. Based on this we investigated the role of single nucleotide polymorphisms (SNPs) within RANK, RANKL and OPG and their possible association to breast cancer risk.

Methods

Genomic DNA was obtained from Caucasian participants consisting of 307 female breast cancer patients and 396 gender-matched healthy controls. We studied seven SNPs in the genes of OPG (rs3102735, rs2073618), RANK (rs1805034, rs35211496) and RANKL (rs9533156, rs2277438, rs1054016) using TaqMan genotyping assays. Statistical analyses were performed using the χ²-tests for 2 x 2 and 2 x 3 tables.

Results

The allelic frequencies (OR: 1.508 CI: 1.127-2.018, p=0.006) and the genotype distribution (p=0.019) of the OPG SNP rs3102735 differed significantly between breast cancer patients and healthy controls. The minor allele C and the corresponding homo- and heterozygous genotypes are more common in breast cancer patients (minor allele C: 18.4% vs. 13.0%; genotype CC: 3.3% vs. 1.3%; genotype CT: 30.3% vs. 23.5%). No significantly changed risk was detected in the other investigated SNPs. Additional analysis showed significant differences when comparing patients with invasive vs. non-invasive tumors (OPG rs2073618) as well as in terms of tumor localization (RANK rs35211496) and body mass index (RANKL rs9533156 and rs1054016).

Conclusions

This is the first study reporting a significant association of the SNP rs3102735 (OPG) with the susceptibility to develop breast cancer in the Caucasian population.

Sex-specific effects of estrogen and androgen on gene expression in human monocyte-derived osteoclasts

Estrogen and androgen are both critical for the maintenance of bone, but the target cells, mechanisms, and responses could be sex-specific. To compare sex-specific actions of estrogen and androgen on osteoclasts, human peripheral blood mononuclear precursor cells from adult Caucasian males (n = 3) and females (n = 3) were differentiated into osteoclasts and then treated for 24 h with 17β-estradiol (10 nM) or testosterone (10 nM). Gene expression was studied with a custom designed qPCR-based array containing 94 target genes related to bone and hormone action. In untreated osteoclasts, 4 genes showed significant gender differences. 17β-estradiol significantly affected 12 genes in osteoclasts from females and 6 genes in osteoclasts from males. Fifteen of the 18 17β-estradiol-responsive genes were different in the cells from the two sexes; 2 genes affected by 17β-estradiol in both sexes were regulated oppositely in the two sexes. Testosterone significantly affected 6 genes in osteoclasts from females and 2 genes in osteoclasts from males; all except one were different in the two sexes. 17β-estradiol and testosterone largely affected different genes, suggesting that conversion of testosterone to 17β-estradiol had a limited role in the responses. The findings indicate that although osteoclasts from both sexes respond to 17β-estradiol and testosterone, the effects of both 17β-estradiol and testosterone differ in the two sexes, highlighting the importance of considering gender in the design of therapy.

"Single nucleotide polymorphisms of the OPG/RANKL system genes in primary hyperparathyroidism and their relationship with bone mineral density"

Background

Primary hyperparathyroidism (PHPT) affects mainly cortical bone. It is thought that parathyroid hormone (PTH) indirectly regulates the activity of osteoclasts by means of the osteoprotegerin/ligand of the receptor activator of nuclear factor-κβ (OPG/RANKL) system. Several studies have confirmed that OPG (osteoprotegerin) and RANKL (ligand of the receptor activator of nuclear factor-κβ) loci are determinants of bone mineral density (BMD) in the general population. The aim of this study is to analyze the relationship between fractures and BMD and the rs3102735 (163 A/G), rs3134070 (245 T/G) and rs2073618 (1181 G/C) SNPs of the OPG and the rs2277438 SNP of the RANKL, in patients with sporadic PHPT.

Methods

We enrolled 298 Caucasian patients with PHPT and 328 healthy volunteers in a cross-sectional study. We analyzed anthropometric data, history of fractures or renal lithiasis, biochemical determinants including markers for bone remodelling, BMD measurements in the lumbar spine, total hip, femoral neck and distal radius, and genotyping for the SNPs to be studied.

Results

Regarding the age of diagnosis, BMI, menopause status, frequency of fractures or renal lithiasis, we found no differences between genotypes in any of the SNPs studied in the PHPT group. Significant lower BMD in the distal radius with similar PTH levels was found in the minor allele homozygotes (GG) compared to heterozygotes and major allele homozygotes in both OPG rs3102735 (163 A/G) and OPG rs3134070 (245 T/G) SNPs in those with PHPT compared to control subjects. We found no differences between genotypes of the OPG rs2073618 (1181 G/C) SNP with regard to BMD in the PHPT subjects. In the evaluation of rs2277438 SNP of the RANKL in PHPT patients, we found a non significant trend towards lower BMD in the 1/3 distal radius and at total hip in the minor allele homocygotes (GG) genotype group versus heterocygotes and major allele homocygotes (AA).

Conclusions

Our study provides the first evaluation of the relationship between SNPs of the OPG/RANK system and sporadic PHPT. Subjects with PHPT and minor homocygote genotype (GG) for the OPG rs3102735 (163 A/G) and OPG rs3134070 (245 T/G) SNPs have lower BMD in the distal radius, and this association does not appear to be mediated by differences in PTH serum levels.

Influence of polymorphisms in the RANKL/RANK/OPG signaling pathway on volumetric bone mineral density and bone geometry at the forearm in men

We sought to determine the influence of single-nucleotide polymorphisms (SNPs) in RANKL, RANK, and OPG on volumetric bone mineral density (vBMD) and bone geometry at the radius in men. Pairwise tag SNPs (r (2) ≥ 0.8) for RANKL (n = 8), RANK (n = 44), and OPG (n = 22) and five SNPs near RANKL and OPG strongly associated with areal BMD in genomewide association studies were previously genotyped in men aged 40-79 years in the European Male Ageing Study (EMAS). Here, these SNPs were analyzed in a subsample of men (n = 589) who had peripheral quantitative computed tomography (pQCT) performed at the distal (4%) and mid-shaft (50%) radius. Estimated parameters were total and trabecular vBMD (mg/mm(3)) and cross-sectional area (mm(2)) at the 4% site and cortical vBMD (mg/mm(3)); total, cortical, and medullary area (mm(2)); cortical thickness (mm); and stress strain index (SSI) (mm(3)) at the 50% site. We identified 12 OPG SNPs associated with vBMD and/or geometric parameters, including rs10505348 associated with total vBMD (β [95% CI] = 9.35 [2.12-16.58], P = 0.011), cortical vBMD (β [95% CI] = 5.62 [2.10-9.14], P = 0.002), cortical thickness (β [95% CI] = 0.08 [0.03-0.13], P = 0.002), and medullary area (β [95% CI] = -2.90 [-4.94 to -0.86], P = 0.005) and rs2073618 associated with cortical vBMD (β [95% CI] = -4.30 [-7.78 to -0.82], P = 0.015) and cortical thickness (β [95% CI] = -0.08 [-0.13 to -0.03], P = 0.001). Three RANK SNPs were associated with vBMD, including rs12956925 associated with trabecular vBMD (β [95% CI] = -7.58 [-14.01 to -1.15], P = 0.021). There were five RANK SNPs associated with geometric parameters, including rs8083511 associated with distal radius cross-sectional area (β [95% CI] = 8.90 [0.92-16.88], P = 0.029). No significant association was observed between RANKL SNPs and pQCT parameters. Our findings suggest that genetic variation in OPG and RANK influences radius vBMD and geometry in men.

TNFRSF11B gene haplotype and its association with bone mineral density variations in postmenopausal Mexican-Mestizo women

OBJECTIVE

Osteoporosis is a complex health disease characterized by low bone mineral density (BMD), which is determined by an interaction of genetics with metabolic and environmental factors. The tumor necrosis factor receptor superfamily, member 11b (TNFRSF11B) gene, has been investigated in relation to BMD. Three polymorphisms in/nearby TNFRSF11B have been associated with BMD variations in some populations. The aim of this study was to investigate the possible association among three SNPs of TNFRSF11B and their haplotypes with the presence of BMD variations in postmenopausal Mexican Mestizo women.

SUBJECTS AND METHODS

One thousand unrelated postmenopausal women of Mexican-Mestizo ethnic origin, who attended the outpatient clinic for routine, general medical evaluation, were invited and 750 women accepted to participate in the study. A structured questionnaire for risk factors was applied and BMD was measured in total hip and lumbar spine by dual-energy X-ray absorptiometry. DNA was obtained from blood leukocytes. Three single-nucleotide polymorphisms in TNFRSF11B gene were studied: rs4355801, rs2073618, and rs6993813. Real-time PCR allelic discrimination was used for genotyping. Deviations from Hardy-Weinberg equilibrium were tested. Pairwise linkage disequilibrium between single nucleotide polymorphisms was calculated by direct correlation r(2), and haplotype analysis was conducted.

RESULTS

Of the subjects, 31% had osteoporosis, 45.1% had osteopenia, and 23.9% had normal BMD. Genotype and allele distributions showed no significant differences; however, A-G-T haplotype was associated with variations in femoral neck BMD (P=0.022).

CONCLUSIONS

In our study population, analysis of the haplotypes of TNFRSF11B is a better genetic marker for variations in BMD.

Insights into the genetics of osteoporosis from recent genome-wide association studies

Osteoporosis, which is characterised by reduced bone mineral density (BMD) and an increased risk of fragility fractures, is the result of a complex interaction between environmental factors and genetic variants that confer susceptibility. Heritability studies have shown that BMD and other osteoporosis-related traits such as ultrasound properties of bone, skeletal geometry and bone turnover have significant inheritable components. Although previous linkage and candidate gene studies have provided few replicated loci for osteoporosis, genome-wide association approaches have produced clear and reproducible findings. To date, 20 genome-wide association studies (GWASs) for osteoporosis and related traits have been conducted, identifying dozens of genes. Further meta-analyses of GWAS data and deep resequencing of rare variants will uncover more novel susceptibility loci and ultimately provide possible therapeutic targets for fracture prevention.

TNFRSF11B gene polymorphisms 1181G > C and 245T > G as well as haplotype CT influence bone mineral density in postmenopausal women

OBJECTIVES

Osteoprotegerin (OPG) inhibits osteoclast function by acting as a decoy receptor for receptor activator of nuclear factor-κB ligand (RANKL), thus being an important candidate gene for osteoporosis. Three recent genome-wide association studies also identified the TNFRSF11B gene, coding for OPG, as playing a key role in bone mineral density (BMD) regulation. As variations in the TNFRSF11B gene could alter the susceptibility to osteoporosis, the aim of study was to investigate association of two TNFRSF11B gene polymorphisms with BMD and serum OPG concentration in postmenopausal women.

STUDY DESIGN

478 postmenopausal women were genotyped for the presence of TNFRSF11B gene polymorphisms 245T > G (rs3134069) and 1181G > C (rs2073618). BMDs and serum OPG concentrations were measured.

RESULTS

Two common haplotypes GT and CT occurred in 41.2% and 52.4% of subjects. In osteoporotic postmenopausal women, lumbar spine BMD was associated with polymorphisms 245T > G and 1181G > C, as well as with CT haplotype (p values 0.013, 0.006 and 0.006, respectively). Additionally, femoral neck BMD showed the association with 245T > G (p = 0.047). No other statistically significant associations with BMD were found for the studied SNPs and haplotypes. No association with serum OPG concentration was shown in any of the studied groups.

CONCLUSIONS

Our results suggest that, in postmenopausal osteoporosis, polymorphisms 245T > G and 1181G > C, as well as haplotype CT in TNFRSF11B gene influence BMD.

Genetic variation in the TNFRSF11A gene encoding RANK is associated with susceptibility to Paget's disease of bone

RANK (receptor activator of nuclear factor-κB), encoded by TNFRSF11A, is a key protein in osteoclastogenesis. TNFRSF11A mutations cause Paget's disease of bone (PDB)-like diseases (ie, familial expansile osteolysis, expansile skeletal hyperphosphatasia, and early-onset PDB) and an osteoclast-poor form of osteopetrosis. However, no TNFRSF11A mutations have been found in classic PDB, neither in familial nor in isolated cases. To investigate the possible relationship between TNFRSF11A polymorphisms and sporadic PDB, we conducted an association study including 32 single-nucleotide polymorphisms (SNPs) in 196 Belgian sporadic PDB patients and 212 control individuals. Thirteen SNPs and 3 multimarker tests (MMTs) turned out to have a p value of between .036 and 3.17 × 10(-4) , with the major effect coming from females. Moreover, 6 SNPs and 1 MMT withstood the Bonferroni correction (p < .002). Replication studies were performed for 2 nonsynonymous SNPs (rs35211496 and rs1805034) in a Dutch and a British cohort. Interestingly, both SNPs resulted in p values ranging from .013 to 8.38 × 10(-5) in both populations. Meta-analysis over three populations resulted in p = .002 for rs35211496 and p = 1.27 × 10(-8) for rs1805034, again mainly coming from the female subgroups. In an attempt to identify the underlying causative SNP, we performed functional studies for the coding SNPs as well as resequencing efforts of a 31-kb region harboring a risk haplotype within the Belgian females. However, neither approach resulted in significant evidence for the causality of any of the tested genetic variants. Therefore, further studies are needed to identify the real cause of the increased risk to develop PDB shown to be present within TNFRSF11A.

Genetics of osteoporosis

Osteoporosis is a common disease with a strong genetic component characterized by reduced bone mass, defects in the microarchitecture of bone tissue, and an increased risk of fragility fractures. Twin and family studies have shown high heritability of bone mineral density (BMD) and other determinants of fracture risk such as ultrasound properties of bone, skeletal geometry, and bone turnover. Osteoporotic fractures also have a heritable component, but this reduces with age as environmental factors such as risk of falling come into play. Susceptibility to osteoporosis is governed by many different genetic variants and their interaction with environmental factors such as diet and exercise. Notable successes in identification of genes that regulate BMD have come from the study of rare Mendelian bone diseases characterized by major abnormalities of bone mass where variants of large effect size are operative. Genome-wide association studies have also identified common genetic variants of small effect size that contribute to regulation of BMD and fracture risk in the general population. In many cases, the loci and genes identified by these studies had not previously been suspected to play a role in bone metabolism. Although there has been extensive progress in identifying the genes and loci that contribute to the regulation of BMD and fracture over the past 15 yr, most of the genetic variants that regulate these phenotypes remain to be discovered.

Genetic epidemiology of age-related osteoporosis and its clinical applications

Osteoporosis is an important and complex disorder that is highly prevalent worldwide. This disease poses a major challenge to modern medicine and its treatment is associated with high costs. Numerous studies have endeavored to decipher the pathogenesis of this disease. The clinical assessment of patients often incorporates information about a family history of osteoporotic fractures. Indeed, the observation of an increased risk of fracture in an individual with a positive parental history of hip fracture provides strong evidence for the heritability of osteoporosis. The onset and progression of osteoporosis are generally controlled by multiple genetic and environmental factors, as well as interactions between them, with rare cases determined by a single gene. In an attempt to identify the genetic markers of complex diseases such as osteoporosis, there has been a move away from traditional linkage mapping studies and candidate gene association studies to higher-density genome-wide association studies. The advent of high-throughput technology enables genotyping of millions of DNA markers in the human genome, and consequently the identification and characterization of causal variants and loci that underlie osteoporosis. This Review presents an overview of the major findings since 2007 and clinical applications of these genome-wide linkage and association studies.

Genetic variation in the RANKL/RANK/OPG signaling pathway is associated with bone turnover and bone mineral density in men

The aim of this study was to determine if single-nucleotide polymorphisms (SNPs) in RANKL, RANK, and OPG influence bone turnover and bone mineral density (BMD) in men. Pairwise tag SNPs (r(2) > or = 0.8) were selected for RANKL, RANK, and OPG and their 10-kb flanking regions. Selected tag SNPs plus five SNPs near RANKL and OPG, associated with BMD in published genome-wide association studies (GWAS), were genotyped in 2653 men aged 40 to 79 years of age recruited for participation in a population-based study of male aging, the European Male Ageing Study (EMAS). N-terminal propeptide of type I procollagen (PINP) and C-terminal cross-linked telopeptide of type I collagen (CTX-I) serum levels were measured in all men. BMD at the calcaneus was estimated by quantitative ultrasound (QUS) in all men. Lumbar spine and total-hip areal BMD (BMD(a)) was measured by dual-energy X-ray absorptiometry (DXA) in a subsample of 620 men. Multiple OPG, RANK, and RANKL SNPs were associated with bone turnover markers. We also identified a number of SNPs associated with BMD, including rs2073618 in OPG and rs9594759 near RANKL. The minor allele of rs2073618 (C) was associated with higher levels of both PINP (beta = 1.83, p = .004) and CTX-I (beta = 17.59, p = 4.74 x 10(-4)), and lower lumbar spine BMD(a) (beta = -0.02, p = .026). The minor allele of rs9594759 (C) was associated with lower PINP (beta = -1.84, p = .003) and CTX-I (beta = -27.02, p = 6.06 x 10(-8)) and higher ultrasound BMD at the calcaneus (beta = 0.01, p = .037). Our findings suggest that genetic variation in the RANKL/RANK/OPG signaling pathway influences bone turnover and BMD in European men.

Polymorphisms and haplotypes across the osteoprotegerin gene associated with bone mineral density and osteoporotic fractures

Osteoprotegerin plays a key role in bone remodelling. We studied the association between 24 polymorphisms and haplotypes on the OPG gene and bone mineral density and fractures. After multiple-testing correction, one SNP and two block-haplotypes were significantly associated with FN BMD. Two other block-haplotypes were associated with fracture.

INTRODUCTION AND HYPOTHESIS

Osteoprotegerin (OPG) plays a key role in bone remodelling. Here we studied the association between polymorphisms and haplotypes on the OPG gene and bone mineral density (BMD) and fractures.

METHODS

Twenty-four single nucleotide polymorphisms (SNPs) were selected to cover six haplotypic blocks and were genotyped in 964 postmenopausal Spanish women. Haplotypes were established with HaploStats. Association was analysed by GLM (for BMD) and logistic regression (for fractures) both at single SNP and haplotype levels.

RESULTS

Upon adjustment for multiple testing (p < 0.0073), one of the SNPs (SNP #17, rs1032129) remained significantly associated with FN BMD (p = 0.001). Four block-haplotypes stood multiple-testing correction. Two remained associated with FN BMD and two with fracture. The association of block-4 haplotype "AC" (of SNPs #18 and #17) with FN BMD (p = 0.0002) was stronger than that of SNP#17 alone and was the best result overall. A global assessment of the results indicated that all the alleles and haplotypes with a protective effect, at p < 0.05, belonged to a frequent long-range haplotype.

CONCLUSIONS

In conclusion, these results provide a detailed picture of the involvement of common variants and haplotypes of the OPG gene in bone phenotypes.

Gene-gene interactions in RANK/RANKL/OPG system influence bone mineral density in postmenopausal women

Receptor activator of nuclear factor kappaB (RANK) is one of the proteins in regulation of osteoclastogenesis via RANK/RANKL/OPG. Gene that codes for RANK protein (TNFRSF11A) was associated with osteoporotic fractures in a recent genome-wide association study. As variations in the RANK gene could alter its expression and activity, the aim of our study was to evaluate the influence of four RANK gene polymorphisms on bone mineral density (BMD) and biochemical markers. We evaluated 467 postmenopausal women and 117 elderly men. All subjects were genotyped for the presence of RANK polymorphisms -670G>C, +34694C>T, +34901G>A and +35966insdelC. BMD and biochemical markers were measured. Significant associations of +35966insdelC with BMD at lumbar spine (BMD-ls), total hip (BMD-th) and femoral neck (BMD-fn) were found in postmenopausal women (p=0.020, 0.024 and 0.034), but not in men. Significant gene-gene interaction was proved for two RANK polymorphisms in combination with OPG and RANKL polymorphisms studied previously in postmenopausal women. Firstly, RANK/RANKL (+34901G>A/-290C>T) combination was associated with BMD-fn, BMD-th and BMD-ls (p=0.034, 0.016 and 0.050), and secondly, RANK/OPG combination (+35966insdelC/K3N) showed influence on BMD-fn and BMD-ls (p=0.043 and 0.039). Our results suggest that gene-gene interactions between RANK and OPG, and RANK and RANKL influence BMD in postmenopausal women.

Genetics of osteoporosis: accelerating pace in gene identification and validation

Osteoporosis is characterized by low bone mineral density and structural deterioration of bone tissue, leading to an increased risk of fractures. It is the most common metabolic bone disorder worldwide, affecting one in three women and one in eight men over the age of 50. In the past 15 years, a large number of genes have been reported as being associated with osteoporosis. However, only in the past 4 years we have witnessed an accelerated pace in identifying and validating osteoporosis susceptibility loci. This increase in pace is mostly due to large-scale association studies, meta-analyses, and genome-wide association studies of both single nucleotide polymorphisms and copy number variations. A comprehensive review of these developments revealed that, to date, at least 15 genes (VDR, ESR1, ESR2, LRP5, LRP4, SOST, GRP177, OPG, RANK, RANKL, COLIA1, SPP1, ITGA1, SP7, and SOX6) can be reasonably assigned as confirmed osteoporosis susceptibility genes, whereas, another >30 genes are promising candidate genes. Notably, confirmed and promising genes are clustered in three biological pathways, the estrogen endocrine pathway, the Wnt/beta-catenin signaling pathway, and the RANKL/RANK/OPG pathway. New biological pathways will certainly emerge when more osteoporosis genes are identified and validated. These genetic findings may provide new routes toward improved therapeutic and preventive interventions of this complex disease.

Association between osteoprotegerin gene polymorphism and bone mineral density in patients with adolescent idiopathic scoliosis

Generalized low bone mass and osteopenia have been reported in the axial and peripheral skeleton of adolescent idiopathic scoliosis (AIS) patients. Recently, many studies have shown that gene polymorphisms are related to osteoporosis. However, no studies have linked the association between gene polymorphisms and bone mass of AIS. Therefore, this study examined the association between the bone mass and RANKL, RANK, and OPG gene polymorphisms in 198 girls diagnosed with AIS. OPG 163 A --> G, 209 G --> A, 245 T --> G, and 1181 G --> C polymorphisms; RANK 421 C --> T and 575 C --> T polymorphisms; and RANKL rs12721445 and rs2277438 polymorphisms, as well as the bone mineral density at the lumbar spine (LSBMD) and femoral neck (FNBMD) were analyzed. The 163 A --> G, 209 G --> A, and 245 T --> G polymorphisms in the OPG gene were in complete linkage. No RANK 421 C --> T and 575 C --> T polymorphisms or RANKL rs12711445 polymorphism were observed. There was a significant association between the OPG gene 1181 G --> C polymorphism and LSBMD. LSBMD in AIS with the CC genotype was found to be significantly higher than in AIS with the GC (P < 0.05) or GG (P < 0.01) genotype. However, there was no significant association between LSBMD or FNBMD and the OPG gene 245 T --> G polymorphism or the RANKL rs2277438 polymorphism. These results suggest that the OPG gene 1181 G --> C polymorphism is associated with LSBMD in girls with AIS.

Genetics of osteoporosis

Osteoporosis is a frequent skeletal disorder, particularly among postmenopausal women. It affects approximately 30% of women and 12% of men above 50 years of age. It is characterized by reduced bone mass and alterations in bone microarchitecture that result in impaired bone strength and a propensity to fracture. Decreased bone mass is the consequence of an imbalance in the bone remodeling process, resulting from complex interactions between acquired and genetic factors. The former include physical activity, nutrition and other lifestyle habits, as well as the skeletal effects of some diseases and drug therapies. Genetic factors have been extensively studied during the past 15 years. We will review some important studies that exemplify the advances and the difficulties in this research field.

Association of aromatase and estrogen receptor gene polymorphisms with hip fractures

Two polymorphisms of the aromatase and estrogen receptor genes appeared to interact to influence the risk of hip fractures in women.

INTRODUCTION

Allelic variants of the aromatase gene have been associated with bone mineral density and vertebral fractures. Our objective was to analyze the relationship between two polymorphisms of the aromatase and estrogen receptor genes and hip fractures.

METHODS

We studied 498 women with hip fractures and 356 controls. A C/G polymorphism of the aromatase gene and a T/C polymorphism of the estrogen receptor alpha gene were analyzed using Taqman assays. Aromatase gene expression was determined in 43 femoral neck samples by real-time RT-PCR.

RESULTS

There were no significant differences in the overall distribution of genotypes between the fracture and control groups. However, among women with a TT genotype of the estrogen receptor, the CC aromatase genotype was more frequent in women with fractures than in controls (39 vs. 23%, p = 0.009). Thus, women homozygous for T alleles of estrogen receptor and C alleles of aromatase were at increased risk of fracture (odds ratio 2.0; 95% confidence interval 1.2-3.4). The aromatase polymorphism was associated with RNA levels in bone tissue, which were three times lower in samples with a CC genotype (p = 0.009).

CONCLUSIONS

These common polymorphisms of the aromatase and estrogen receptor genes appear to interact, influencing the risk of hip fractures in women.

Multiple genetic loci for bone mineral density and fractures

BACKGROUND

Bone mineral density influences the risk of osteoporosis later in life and is useful in the evaluation of the risk of fracture. We aimed to identify sequence variants associated with bone mineral density and fracture.

METHODS

We performed a quantitative trait analysis of data from 5861 Icelandic subjects (the discovery set), testing for an association between 301,019 single-nucleotide polymorphisms (SNPs) and bone mineral density of the hip and lumbar spine. We then tested for an association between 74 SNPs (most of which were implicated in the discovery set) at 32 loci in replication sets of Icelandic, Danish, and Australian subjects (4165, 2269, and 1491 subjects, respectively).

RESULTS

Sequence variants in five genomic regions were significantly associated with bone mineral density in the discovery set and were confirmed in the replication sets (combined P values, 1.2x10(-7) to 2.0x10(-21)). Three regions are close to or within genes previously shown to be important to the biologic characteristics of bone: the receptor activator of nuclear factor-kappaB ligand gene (RANKL) (chromosomal location, 13q14), the osteoprotegerin gene (OPG) (8q24), and the estrogen receptor 1 gene (ESR1) (6q25). The two other regions are close to the zinc finger and BTB domain containing 40 gene (ZBTB40) (1p36) and the major histocompatibility complex region (6p21). The 1p36, 8q24, and 6p21 loci were also associated with osteoporotic fractures, as were loci at 18q21, close to the receptor activator of the nuclear factor-kappaB gene (RANK), and loci at 2p16 and 11p11.

CONCLUSIONS

We have discovered common sequence variants that are consistently associated with bone mineral density and with low-trauma fractures in three populations of European descent. Although these variants alone are not clinically useful in the prediction of risk to the individual person, they provide insight into the biochemical pathways underlying osteoporosis.

Osteoprotegerin Lys3Asn polymorphism and the risk of fracture in older women

CONTEXT

Osteoprotegerin (OPG) is a soluble decoy receptor for receptor activator nuclear factor kappa-beta that blocks osteoclastic bone resorption.

OBJECTIVE

We investigated the association between a Lys3Asn polymorphism in the OPG gene and bone mineral density (BMD), and the risk of fracture in 6695 women aged 65 yr and older participating in the Study of Osteoporotic Fractures.

DESIGN

BMD was measured using either single-photon absorptiometry (Osteon Osteoanalyzer; Dove Medical Group, Los Angeles, CA) or dual-energy x-ray absorptiometry (Hologic QDR 1000; Hologic, Inc., Bedford, MA). Incident fractures were confirmed by physician adjudication of radiology reports. Genotyping was performed using an immobilized probe-based assay.

RESULTS

Women who were homozygous for the minor G (Lys) allele had significantly lower BMD at the intertrochanter, distal radius, lumbar spine, and calcaneus than those with the C (Asn) allele. There were 701 incident hip fractures during 13.6-yr follow-up (91,249 person-years), including 362 femoral neck and 333 intertrochanteric hip fractures. Women with the C/C (Asn-Asn) genotype had a 51% higher risk of femoral neck fracture (95% confidence interval, 1.13-2.02) and 26% higher risk of hip fracture (95% confidence interval, 1.02-1.54) than those with the G/G (Lys-Lys) genotype. These associations were independent of BMD. Intertrochanteric fractures were not associated with the Lys3Asn polymorphism.

CONCLUSION

These results require confirmation but suggest a role for the OPG Lys3Asn polymorphism in the genetic susceptibility to hip fractures among older white women.

Estrogen receptor alpha CA dinucleotide repeat polymorphism is associated with rate of bone loss in perimenopausal women and bone mineral density and risk of osteoporotic fractures in postmenopausal women

The association between a newly identified CA repeat polymorphism of the estrogen receptor alpha gene (ESR1) with osteoporosis was investigated. Postmenopausal women with <18 CA repeats had low BMD, increased rate of bone loss and increased fracture risk.

INTRODUCTION

Studies have shown that intronic dinucleotide repeat polymorphisms in some genes are associated with disease risk by modulating mRNA splicing efficiency. D6S440 is a newly identified intronic CA repeat polymorphism located downstream of the 5'-splicing site of exon 5 of ESR1.

METHODS

The associations of D6S440 with bone mineral density (BMD), rate of bone loss and fracture risk were evaluated in 452 pre-, 110 peri- and 622 postmenopausal southern Chinese women using regression models.

RESULTS

Post- but not premenopausal women with less CA repeats had lower spine and hip BMD. The number of CA repeats was linearly related to hip BMD in postmenopausal women (beta=0.008; p=0.004). Postmenopausal women with CA repeats <18 had higher risks of having osteoporosis (BMD T-score< -2.5 at the spine: OR 2.46, 95% CI 1.30-4.65; at the hip: OR 3.79(1.64-8.74)) and low trauma fractures (OR 2.31(1.29-4.14)) than those with >or= 18 repeats. Perimenopausal women with <18 CA repeats had significantly greater bone loss in 18 months at the hip than those with >or= 18 repeats (-1.96% vs. -1.61%, p = 0.029).

CONCLUSIONS

ESR1 CA repeat polymorphism is associated with BMD variation, rate of bone loss and fracture risk, and this may be a useful genetic marker for fracture risk assessment.

Molecular genetic studies of gene identification for osteoporosis

This review comprehensively summarizes the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of September 2007. It is intended to constitute a sequential update of our previously published reviews covering the available data up to the end of 2004. Evidence from candidate gene-association studies, genome-wide linkage and association studies, as well as functional genomic studies (including gene-expression microarray and proteomics) on osteogenesis and osteoporosis, are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. The major results of all studies are tabulated for comparison and ease of reference. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Dimorphic effects of Notch signaling in bone homeostasis

Notch signaling is a key mechanism in the control of embryogenesis. However, its in vivo function during mesenchymal cell differentiation, and, specifically, in bone homeostasis, remains largely unknown. Here, we show that osteoblast-specific gain of Notch function causes severe osteosclerosis owing to increased proliferation of immature osteoblasts. Under these pathological conditions, Notch stimulates early osteoblastic proliferation by upregulating the genes encoding cyclin D, cyclin E and Sp7 (osterix). The intracellular domain of Notch1 also regulates terminal osteoblastic differentiation by directly binding Runx2 and repressing its transactivation function. In contrast, loss of all Notch signaling in osteoblasts, generated by deletion of the genes encoding presenilin-1 and presenilin-2 in bone, is associated with late-onset, age-related osteoporosis, which in turn results from increased osteoblast-dependent osteoclastic activity due to decreased osteoprotegerin mRNA expression in these cells. Together, these findings highlight the potential dimorphic effects of Notch signaling in bone homeostasis and may provide direction for novel therapeutic applications.

Pathogenesis of calciphylaxis: Hans Selye to nuclear factor kappa-B

The clinical syndrome of calciphylaxis is characterized by arteriolar medial calcification, thrombotic cutaneous ischemia, necrotic skin ulceration, and a high mortality rate. This review integrates calciphylaxis risk factors with the molecular processes governing osseous and extraosseous mineralization. As the pathogenesis of calciphylaxis is better understood, targeted therapies aimed at disease prevention and reversal will follow.

Association between osteoprotegerin (OPG), receptor activator of nuclear factor-kappaB (RANK), and RANK ligand (RANKL) gene polymorphisms and circulating OPG, soluble RANKL levels, and bone mineral density in Korean postmenopausal women

OBJECTIVE

To investigate the association between osteoprotegerin (OPG), receptor activator of nuclear factor-kappaB (RANK), and RANK ligand (RANKL) gene polymorphisms and circulating OPG, soluble RANKL (sRANKL) levels, and bone mineral density (BMD) in Korean postmenopausal women.

DESIGN

The OPG gene A163G, G209A, T245G, and G1181C polymorphisms, the RANK gene C421T and C575T polymorphisms, and the RANKL rs12721445 and rs2277438 polymorphisms were analyzed in 385 Korean postmenopausal women. Levels of serum OPG, soluble RANKL, osteocalcin, C-telopeptide of type I collagen, parathyroid hormone, calcium, and phosphorus and BMD at the lumbar spine and femoral neck were measured.

RESULTS

The A163G, G209A, and T245G polymorphisms in the OPG gene were in complete linkage. The RANK C421T and C575T polymorphisms and the RANKL rs12711445 polymorphism were not observed. An association with BMD was found only for the OPG G1181C polymorphism, and BMD at the lumbar spine in women with the CC genotype was significantly higher than in women with the GC or GG genotype, with a C allele dose effect. In itself, the RANKL rs2277438 polymorphism was not related to BMD, but by combining the RANKL genotypes with the GC genotypes of the OPG G1181C polymorphism, the association with BMD at the lumbar spine became significant. No significant differences in the levels of any biochemical marker among genotypes of these polymorphisms were found.

CONCLUSIONS

The OPG gene G1181C polymorphism, alone and in combination with the RANKL rs2277438 polymorphism, was identified as a genetic factor associated with BMD of the lumbar spine in Korean women.