A haplotype-based analysis of the LRP5 gene in relation to osteoporosis phenotypes in Spanish postmenopausal women

Associations of IDUA and PTCH1 with Bone Mineral Density, Bone Turnover Markers, and Fractures in Chinese Elderly Patients with Osteoporosis

Introduction

Osteoporosis (OP) is a common polygenic disorder in the aging population, and several single nucleotide polymorphisms (SNPs) in the alpha-L-iduronidase (IDUA) gene and patched homolog 1 (PTCH1) gene regulate bone metabolism and affect bone mass. The study aimed at investigating the relationships of rs3755955 and rs6831280 in the IDUA gene and rs28377268 in the PTCH1 gene with bone mineral density (BMD), bone turnover markers (BTMs), and fractures in the elderly Chinese subjects with OP.

Materials and Methods

A cohort of 328 unrelated senile osteoporosis (SOP) patients with or without osteoporotic fractures was recruited. rs3755955, rs6831280, and rs28377268 polymorphisms were identified using SNaPshot technology. BTM levels were determined by electrochemiluminescence (ECL). Bone mineral densities (BMDs) at the lumbar spine (LS) and proximal femur sites were measured by dual-energy X-ray absorptiometry (DEXA) in all subjects. The Hardy-Weinberg equilibrium (HWE) test was performed. HWE P values and comparisons of genotype frequencies were estimated using the chi-square test. Analysis of covariance (ANCOVA) adjusted for confounding factors was performed to investigate associations of SNPs with BMDs and BTMs in subgroups.

Results

The chi-square test indicated that genotype distributions in the control group conformed to HWE (P > 0.05). The distributions of allele and genotype frequencies of rs6831280 between fracture and osteoporotic participants were significantly different (P-allele = 0.002 and P-genotype = 0.012, respectively). Concerning rs6831280, ANCOVA found BMDs at LS 2-4 (L2-4) and total hip (TH) among the study subjects suffering from SOP with GA genotype were lower than in those carrying GG or AA (P-L2-4 = 0.004 and P-TH = 0.027, respectively).

Conclusions

IDUA rs6831280 is associated with BMDs at L2-4 and TH in the elderly Chinese population with SOP and may serve as a marker for the genetic susceptibility to osteoporotic fractures.

LRP5 gene polymorphisms and radiographic joint damage in rheumatoid arthritis patients

Rheumatoid arthritis (RA) is characterized by increased bone resorption and impaired bone formation. Osteoblast function is regulated by the canonical LRP5/Wnt/β-catenin pathway. Bone mineral density and RA joint destruction are partially inherited. In line with this, we found significant associations between LRP5 SNPs (p.A1330V, p.N740N, p.V667M) and RA radiographic damage severity.

INTRODUCTION

Increased bone resorption and impaired bone formation characterize rheumatoid arthritis (RA). Canonical Wnt/β-catenin pathway, signalled by lipoprotein receptor-related protein-5 (LRP5), regulates osteoblast function. Since bone mineral density (BMD) and RA joint destruction are partially inherited, we studied their association with LRP5 single nucleotide polymorphisms (SNPs).

METHODS

Clinical data and peripheral blood for biomarkers assessment and LRP5 genotyping were collected from 208 RA patients. Hands and feet X-rays were scored [modified Sharp/van der Heijde Score (SHS), joint space narrowing (JSN), and erosion scores]. Lumbar spine, total left proximal femur, and left hand BMD were assessed by dual-energy X-ray absorptiometry (DXA).

RESULTS

TT genotypes for p.A1330V and p.N740N LRP5 SNPs associated with total SHS, erosion score, and hands erosion score; the same for p.A1330V with feet JSN score and p.N740N with hands total score. AG genotype for p.V667M associated with sclerostin and hands JSN score. Femoral BMD associated with TC genotype for p.N740N. Multiple test correction precluded a few of these associations. Among V667M-N740N-A1330V haplotypes: GTT associated with higher feet JSN score (OR = 3.80; p = 0.016) and ATT with higher JSN score (OR = 4.60; p = 0.032), hands total score (OR = 5.65; p = 0.022), and total SHS (OR = 6.74; p = 0.024).

CONCLUSION

Significant associations between LRP5 SNPs (p.A1330V, p.N740N, and p.V667M) and the severity of radiographic damage reinforce the evidence of bone destruction heritability in RA.

Genome-wide Survey of Runs of Homozygosity Identifies Recessive Loci for Bone Mineral Density in Caucasian and Chinese Populations

Runs of homozygosity (ROHs), in which both parental alleles are identical, have been proposed to have recessive effects on multiple human complex diseases. Osteoporosis is a common complex disease characterized by low bone mineral density (BMD), which is highly heritable. And recessive loci that contribute to BMD variations have been identified. In this study, we performed a genome-wide ROHs association study using our SNP array data from three GWAS samples including 4,900 subjects from Caucasian and Chinese populations. Significant results were further subjected to replication in 3,747 additional subjects. ROHs associated with BMD were also tested for associations with osteoporotic fractures in a GWAS fracture sample. Combining results from all the samples, we identified 697 autosomal regions with ROHs. Among these, we detected genome-wide significant associations between BMD and 6 ROHs, including ROH1q31.3, 1p31.1, 3q26.1, 11q12.1, 21q22.1 and 15q22.3 (combined P = 6.29 × 10(-5)-3.17 × 10(-8)). Especially, ROH1p31.1 was found to be associated with increased risk of osteoporotic hip fractures (odds ratio [OR] = 3.71, P = 0.032). To investigate the functional relevance of the identified ROHs, we performed cis-expression quantitative trait locus (eQTL) analysis in lymphoblast cell lines. Three ROHs, including ROH1p31.1, 11q12.1, and 15q22.3, were found to be significantly associated with mRNA expression levels of their nearby genes (PeQTL < 0.05). In summary, our findings reveal that ROHs could play as recessive-acting determinants contributing to the pathogenesis of osteoporosis. Further molecular and functional studies are needed to explore and clarify the potential mechanism.

Recent genetic discoveries in osteoporosis, sarcopenia and obesity

Osteoporosis is a skeletal disorder characterized by low bone mineral density (BMD) and an increased susceptibility to fractures. Evidence from genetic studies indicates that BMD, a complex quantitative trait with a normal distribution, is genetically controlled. Genome-wide association studies (GWAS) as well as studies using candidate gene approaches have identified single-nucleotide polymorphisms (SNPs) that are associated with BMD, osteoporosis and osteoporotic fractures. These SNPs have been mapped close to or within genes including those encoding WNT/β-catenin signaling proteins. Understanding the genetics of osteoporosis will help to identify novel candidates for diagnostic and therapeutic targets. Genetic factors are also important for the development of sarcopenia, which is characterized by a loss of lean body mass, and obesity, which is characterized by high fat mass. Hence, in this review, we discuss the genetic factors, identified by genetic studies, which regulate the body components related to osteoporosis, sarcopenia, and obesity.

Replication study of three functional polymorphisms associated with bone mineral density in a cohort of Spanish women

Gene candidate and genome-wide association studies have revealed tens of loci of susceptibility for osteoporosis. Some limitations such as sample size, use of confounding variables, and control for multiple testing and for population stratification, however, represent common problems in these studies that make replication in independent cohorts desirable and even necessary. The main objective of the present study is to replicate previous data on three functional polymorphisms in a cohort of Spanish women. To that end, we performed an association study of three functional polymorphisms previously associated with bone phenotypes in the LRP5, TNFRSF11B, and FGFBP1 genes with low bone mineral density (BMD) in a cohort of 721 Spanish women, most of them postmenopausal. We detected a strong significant association, even when correcting for multiple comparisons, for polymorphism rs312009 in the LRP5 gene with low BMD at the lumbar-spine site. These were women with the CC genotype, which showed the worst bone parameters. Moreover, these women had a higher risk of osteoporosis (adjusted odds ratio 2.82, P = 0.001) than women with the TT/TC genotype. This association seems to be caused because the rs312009 single nucleotide polymorphism (SNP) is located at a binding site for the transcription factor RUNX2 at the 5' region of the LRP5 gene, and the T allele seems to be a better transcriber than the C allele. Regarding the other two SNPs, only the rs4876869 SNP in the TNFRSF11B gene showed a suggestive trend for both skeletal sites. These results underscore the significance of the LRP5 gene in bone metabolism and emphasize the significance of the replication of previous results in independent cohorts.

Identification and characterization of the novel Col10a1 regulatory mechanism during chondrocyte hypertrophic differentiation

The majority of human skeleton develops through the endochondral pathway, in which cartilage-forming chondrocytes proliferate and enlarge into hypertrophic chondrocytes that eventually undergo apoptosis and are replaced by bone. Although at a terminal differentiation stage, hypertrophic chondrocytes have been implicated as the principal engine of bone growth. Abnormal chondrocyte hypertrophy has been seen in many skeletal dysplasia and osteoarthritis. Meanwhile, as a specific marker of hypertrophic chondrocytes, the type X collagen gene (COL10A1) is also critical for endochondral bone formation, as mutation and altered COL10A1 expression are often accompanied by abnormal chondrocyte hypertrophy in many skeletal diseases. However, how the type X collagen gene is regulated during chondrocyte hypertrophy has not been fully elucidated. We have recently demonstrated that Runx2 interaction with a 150-bp mouse Col10a1 cis-enhancer is required but not sufficient for its hypertrophic chondrocyte-specific reporter expression in transgenic mice, suggesting requirement of additional Col10a1 regulators. In this study, we report in silico sequence analysis of this 150-bp enhancer and identification of its multiple binding factors, including AP1, MEF2, NFAT, Runx1 and TBX5. Using this enhancer as bait, we performed yeast one-hybrid assay and identified multiple candidate Col10a1-interacting genes, including cyclooxygenase 1 (Cox-1) and Cox-2. We have also performed mass spectrometry analysis and detected EF1-alpha, Fus, GdF7 and Runx3 as components of the specific complex formed by the cis-enhancer and nuclear extracts from hypertrophic MCT (mouse chondrocytes immortalized with large T antigen) cells that express Col10a1 abundantly. Notably, some of the candidate genes are differentially expressed in hypertrophic MCT cells and have been associated with chondrocyte hypertrophy and Runx2, an indispensible Col10a1 regulator. Intriguingly, we detected high-level Cox-2 expression in hypertrophic MCT cells. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays confirmed the interaction between Cox-2 and Col10a1 cis-enhancer, supporting its role as a candidate Col10a1 regulator. Together, our data support a Cox-2-containing, Runx2-centered Col10a1 regulatory mechanism, during chondrocyte hypertrophic differentiation.

4q22.1 contributes to bone mineral density and osteoporosis susceptibility in postmenopausal women of Chinese Han population

Osteoporosis is a multifactorial disease in which genetic determinants are modulated by hormonal, environmental and nutritional factors. An important clinical risk factor in the pathogenesis of osteoporosis is the presence of genetics polymorphism in/around susceptibility genes/regions. This study explored whether the region of 4q22.1, which confers risk of developing osteoporosis in some populations, associated with bone mineral density and osteoporosis susceptibility in postmenopausal women of Han Chinese. We investigated 32 SNPs with minor allele frequencies ≥0.05 between 20 kb upstream and 20 kb downstream (40 kb window) of rs6532023, mapping in the 4q22.1 region, which was reported to be significantly associated with osteoporosis in previous studies. We found that rs6532023 was significantly associated with bone mineral density and osteoporosis (corrected p = 0.015) in our sample, including 440 cases and 640 controls, and allele G was supposed as a risk factor while T worked as a protective factor. Further genotype association analyses suggested a similar pattern (corrected p = 0.040). Additionally, analyses by haplotypes indicated that a haplotype block rs7683315-rs6532023-rs1471400-rs1471403 in the region associated with bone mineral density and osteoporosis (global p = 0.032), and risk haplotype A-G-G-C had almost 1.5-fold increased in the cases. To our knowledge, this is the first report to examine 4q22.1 region polymorphisms and osteoporosis in Han Chinese. Our results provide further evidence for an effect of the region of 4q22.1 on the etiology of osteoporosis and suggest that 4q22.1 may be a genetic risk factor for bone mineral density and osteoporosis.

Genetic polymorphisms of the Wnt receptor LRP5 are differentially associated with trochanteric and cervical hip fractures

Epidemiological studies suggest that cervical and trochanteric hip fractures have different pathogenesis. We tested the hypothesis that genetic factors have different influences on both types of fractures. Ten polymorphisms of genes known to play an important role in skeletal homeostasis [estrogen receptor alpha (ESR1), aromatase (CYP19A1), type I collagen (COL1A1), and lipoprotein receptor-related protein 5 (LRP5)] were analyzed in 471 Spanish patients with fragility hip fractures. Two polymorphisms of the LRP5 gene (rs7116604 and rs3781600) were associated with the type of fracture (P = 0.0085 and 0.0047, respectively). The presence of rare alleles at each locus was associated with trochanteric fractures over cervical fractures (OR = 1.7 in individuals with at least one rare allele at rs7116604 or rs3781600 loci in comparison with the common homozygotes). Considering individuals bearing the four common alleles as reference, the OR for trochanteric fractures was 1.6 in those with one or two rare alleles and 7.5 in those with three or four rare alleles (P for trend = 0.0074), which is consistent with an allele-dosage effect. There were no significant differences in the frequency distributions of the ESR1, CYP19A1, and COL1A1 genotypes between trochanteric and cervical fractures in either the original group or an extended group of 818 patients. These results suggest that LRP5 alleles influence the type of hip fractures. They support the view that different genetic factors are involved in cervical and trochanteric fractures, which should be taken into consideration in future genetic association studies.

Runx2 contributes to murine Col10a1 gene regulation through direct interaction with its cis-enhancer

We have recently shown that a 150-bp Col10a1 distal promoter (-4296 to -4147 bp) is sufficient to direct hypertrophic chondrocyte-specific reporter (LacZ) expression in vivo. More recently, through detailed sequence analysis we identified two putative tandem-repeat Runx2 binding sites within the 3'-end of this 150-bp region (TGTGGG-TGTGGC, -4187 to -4176 bp). Candidate electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation, and transfection studies demonstrate that these putative Runx2 sites bind Runx2 and mediate upregulated Col10a1/reporter activity in vitro. Transgenic studies using the 5'-sequence without Runx2 sites were not able to drive the cell-specific LacZ reporter activity, suggesting the in vivo requirement of the Runx2 sites located in the 3'-end in mediating Col10a1/reporter expression. Indeed, mutating the Runx2 sites in the context of the 150-bp promoter abolishes its capacity to drive hypertrophic chondrocyte-specific reporter expression in transgenic mice. We have also generated multiple transgenic mouse lines using only the 3'-sequence containing the Runx2 sites to drive the LacZ gene. Interestingly, no hypertrophic chondrocyte-specific blue staining was observed in these transgenic mice. Together, our data support that Runx2 directly interacts with murine Col10a1 cis-enhancer. This interaction is required but not sufficient for cell-specific Col10a1 promoter activity in vivo. Additional cooperative/repressive elements within the 5'- or 3'-sequences of this 150-bp promoter are needed to work with Runx2 together to mediate cell-specific Col10a1 expression. Further delineation of these elements/factors has the potential to identify novel therapeutic targets for multiple skeletal disorders, including osteoarthritis, that show abnormal Col10a1 expression and altered chondrocyte maturation.

Functional relevance of the BMD-associated polymorphism rs312009: novel involvement of RUNX2 in LRP5 transcriptional regulation

LRP5 is an osteoporosis susceptibility gene. Association analyses reveal that individual single-nucleotide polymorphisms (SNPs) determine variation in bone mineral density (BMD) among individuals as well as fracture risk. In a previous study, we identified a lumbar spine BMD-associated SNP, rs312009, located in the LRP5 5' region. A RUNX2 binding site was identified in this region by gel-shift experiments. Here we test the functionality of this SNP and examine whether RUNX2 is indeed a regulator of LRP5 expression. Gene reporter assays were used to test rs312009 functionality. Bioinformatic predictive tools and gel-shift and gene reporter assays were used to identify and characterize additional RUNX2 binding elements in the 3.3-kb region upstream of LRP5. Allelic differences in the transcriptional activity of rs312009 were observed in two osteoblastic cell lines, the T allele being a better transcriber than the C allele. RUNX2 cotransfection in HeLa cells revealed that the LRP5 5' region responded to RUNX2 in a dose-dependent manner and that the previously identified RUNX2 binding site participated in this response. Also, RUNX2 inhibition by RNAi led to nearly 60% reduction of endogenous LRP5 mRNA in U-2 OS cells. Four other RUNX2 binding sites were identified in the 5' region of LRP5. Luciferase experiments revealed the involvement of each of them in the RUNX2 response. The allelic differences observed point to the involvement of rs312009 as a functional SNP in the observed association. To our knowledge, this is the first time that the direct action of RUNX2 on LRP5 has been described. This adds evidence to previously described links between two important bone-regulating systems: the RUNX2 transcription-factor cascade and the Wnt signaling pathway.

Wnt receptors, bone mass, and fractures: gene-wide association analysis of LRP5 and LRP6 polymorphisms with replication

OBJECTIVE

Genes explaining the susceptibility to osteoporosis have not been fully elucidated. Our objective was to explore the association of polymorphisms capturing common variations of the lipoprotein receptor-related protein (LRP) 5 and 6 genes, encoding two Wnt receptors, with femoral neck bone mineral density (BMD) and osteoporotic fractures of the spine and the hip.

DESIGN

Cross-sectional, case-control, and replication genetic association study.

METHODS

Thirty-nine tagging and functional single nucleotide polymorphisms (SNPs) were analyzed in a group of 1043 postmenopausal women and 394 women with hip fractures. The results were replicated in a different group of 342 women.

RESULTS

Three SNPs of the LRP6 gene were associated with BMD (nominal uncorrected P values <0.05) in the discovery cohort. One showed a significant association after multiple test correction; two of them were also associated in the replication cohort, with a combined standardized mean difference of 0.51 (P=0.009) and 0.47 (P<0.003) across rs11054704 and rs2302685 genotypes. In the discovery cohort, several LRP5 SNPs were associated with vertebral fractures (odds ratio (OR) 0.67; P=0.01), with hip fractures (unadjusted ORs between 0.59 and 1.21; P=0.005-0.033, but not significant after multiple test adjustment or age adjustment), and with height and the projected femoral neck area, but not with BMD. Transcripts of LRP5 and LRP6 were similarly abundant in bone samples.

CONCLUSIONS

In this study, we found common polymorphisms of LRP5 associated with osteoporotic fractures, and polymorphisms of the LRP6 gene associated with BMD, thus suggesting them as likely candidates to contribute to the explaination of the hereditary influence on osteoporosis.

Molecular genetic studies of gene identification for osteoporosis: the 2009 update

Osteoporosis is a complex human disease that results in increased susceptibility to fragility fractures. It can be phenotypically characterized using several traits, including bone mineral density, bone size, bone strength, and bone turnover markers. The identification of gene variants that contribute to osteoporosis phenotypes, or responses to therapy, can eventually help individualize the prognosis, treatment, and prevention of fractures and their adverse outcomes. Our previously published reviews have comprehensively summarized the progress of molecular genetic studies of gene identification for osteoporosis and have covered the data available to the end of September 2007. This review represents our continuing efforts to summarize the important and representative findings published between October 2007 and November 2009. The topics covered include genetic association and linkage studies in humans, transgenic and knockout mouse models, as well as gene-expression microarray and proteomics studies. Major results are tabulated for comparison and ease of reference. Comments are made on the notable findings and representative studies for their potential influence and implications on our present understanding of the genetics of osteoporosis.

Analysis of three functional polymorphisms in relation to osteoporosis phenotypes: replication in a Spanish cohort

Osteoporosis is a complex disease involving many putative genetic factors. Association analysis of functional SNPs in candidate genes is an important tool for their identification. However, this approach is affected by limited power, population stratification, and other drawbacks that lead to discordant results. Replication in independent cohorts is essential. We performed association analyses of three functional polymorphisms previously associated with bone phenotypes--namely, Ala222Val in MTHFR, Ile1062Val in LRP6, and -13910C>T in LCT--in a cohort of 944 postmenopausal Spanish women, all of them with lumbar spine (LS) bone mineral density (BMD) data and most with femoral neck (FN) BMD and fracture data. We found significant differences between genotypes only for the MTHFR polymorphism and vertebral factures, with an OR of 2.27 (95% CI 1.17-4.38) for the TT vs. CC/CT genotypes, P = 0.018. We present genotype and allele frequency data for LCT -13910C>T for a Spanish population, where the T allele (conferring lactase persistence) has a frequency of 38.6%. Genotype frequencies were consistent with observed clines in Europe and with the prevalence of lactase nonpersistence. The LCT -13910C>T polymorphism was significantly associated with height and weight, such that T allele carriers were 0.88 cm taller (95% CI 0.08-1.59 cm, P = 0.032, adjusted by age) than CC individuals and TT homozygotes were 1.91 kg heavier than CC/CT individuals (95% CI 0.11-3.71 kg, P = 0.038, adjusted by age). In conclusion, no significant association was observed between the studied polymorphisms and LS BMD or FN BMD in postmenopausal Spanish women, and only MTHFR Ala222Val was associated with vertebral fractures.

Replication study of candidate genes/loci associated with osteoporosis based on genome-wide screening

Osteoporosis is a major public health problem characterized by low bone mineral density (BMD). This replication study confirmed 38 single-nucleotide polymorphisms (SNPs) out of 139 SNPs previously reported in three recent genome-wide association studies (GWASs) in an independent US white sample. Ten SNPs achieved combined p < 3.6 x 10(-4).

INTRODUCTION

BMD is under strong genetic control. This study aims to verify the potential associations between BMD and candidate genes/loci reported by GWAS of FHS100K, Icelandic deCODE, and UK-NL.

METHODS

Eight promising (at the genome-wide significant level after Bonferroni correction) and 131 available sub-promising (at the most stringent p value, p < 5.5 x 10(-5) in the three GWASs reports) SNPs were selected. By using genotypic information from Affymetrix 500 K SNP arrays, we tested their associations with BMD in 1,000 unrelated US whites. Fisher's combined probability method was used to quantify the overall evidence of association. BMD was measured by dual energy X-ray absorptiometry.

RESULTS

Two promising SNPs, rs3762397 and rs3736228, were replicated in the current study with p < 0.05. Besides, 36 sub-promising SNPs were replicated at the same significant level. Ten SNPs achieved significant combined p < 3.6 x 10(-4) (0.05/139 SNPs, corrected for multiple testing).

CONCLUSIONS

Osteoporosis susceptibility of 38 SNPs was replicated in 1,000 unrelated US whites. This study showed promise for replication of some initial genome-wide association signals.

The role of cigarette smoking and statins in the development of postmenopausal osteoporosis: a pilot study utilizing the Marshfield Clinic Personalized Medicine Cohort

SUMMARY

A cohort of postmenopausal osteoporotic females and controls with normal bone mineral density, the interleukin 6 (IL6) -634G > C (rs1800796) C allele of the promoter region showed association with osteoporosis. The lipoprotein receptor-related protein 5 (LRP5) gene showed association between C135242T C/T alleles and osteoporosis only in smokers, suggesting a role for environmental interaction.

INTRODUCTION

A nested case-control study within a population-based cohort was undertaken to assess the relative impact of cigarette smoking, statin use, genetic polymorphisms, and one-way interaction of these factors on development of osteoporosis in postmenopausal women.

METHODS

Genotyping of 14 single-nucleotide polymorphisms (SNPs) corresponding to vitamin D receptor gene, estrogen receptor 1, collagen type 1 alpha 1, IL6, transcription growth factor beta, apolipoprotein E, and LRP5 genes was performed in cases (n = 309) with osteoporosis and controls (n = 293) with normal bone mineral density drawn from a homogeneous Caucasian population. SNPs were chosen based on known functional consequences or prior evidence for association and genotyped using matrix-assisted laser desorption ionization time-of-flight technology.

RESULTS

Cases differed from controls relative to body mass index, age, and smoking but not statin use. After adjusting for age, the IL6 -634G > C (rs1800796) allele showed association with osteoporosis (odds ratio (OR) for CC + CG = 2.51, p = 0.0047)), independent of statin use or smoking status. On stratification for smoking, association with LRP5 C135242T (rs545382) and osteoporosis emerged (OR 2.8 in smokers for CT alleles, p = 0.03)), suggestive of potential environmental interaction.

CONCLUSION

Evidence suggested a role for genetic variation in IL6 and LRP5 in conferring risk for osteoporosis in Caucasian women, with the latter manifest only in smokers.

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.