Genetic variants in adult bone mineral density and fracture risk genes are associated with the rate of bone mineral density acquisition in adolescence

From Genomics to Metabolomics: Molecular Insights into Osteoporosis for Enhanced Diagnostic and Therapeutic Approaches

Osteoporosis (OP) is a prevalent skeletal disorder characterized by decreased bone mineral density (BMD) and increased fracture risk. The advancements in omics technologies-genomics, transcriptomics, proteomics, and metabolomics-have provided significant insights into the molecular mechanisms driving OP. These technologies offer critical perspectives on genetic predispositions, gene expression regulation, protein signatures, and metabolic alterations, enabling the identification of novel biomarkers for diagnosis and therapeutic targets. This review underscores the potential of these multi-omics approaches to bridge the gap between basic research and clinical applications, paving the way for precision medicine in OP management. By integrating these technologies, researchers can contribute to improved diagnostics, preventative strategies, and treatments for patients suffering from OP and related conditions.

Polymorphisms in the glucagon-like peptide-1 receptor gene and their interactions on the risk of osteoporosis in postmenopausal Chinese women

Postmenopausal osteoporosis (PMOP) is a prevalent form of primary osteoporosis, affecting over 40% of postmenopausal women. Previous studies have suggested a potential association between single nucleotide polymorphisms (SNPs) in glucagon-like peptide-1 receptor (GLP-1R) and PMOP in postmenopausal Chinese women. However, available evidence remains inconclusive. Therefore, this study aimed to investigate the possible association between GLP-1R SNPs and PMOP in Han Chinese women. Thus, we conducted a case-control study with 152 postmenopausal Han Chinese women aged 45-80 years, including 76 women with osteoporosis and 76 without osteoporosis. Seven SNPs of the GLP-1R were obtained from the National Center of Biotechnology Information and Genome Variation Server. We employed three genetic models to assess the association between GLP-1R genetic variants and osteoporosis in postmenopausal women, while also investigating SNP-SNP and SNP-environment interactions with the risk of PMOP. In this study, we selected seven GLP-1R SNPs (rs1042044, rs2268641, rs10305492, rs6923761, rs1126476, rs2268657, and rs2295006). Of these, the minor allele A of rs1042044 was significantly associated with an increased risk of PMOP. Genetic model analysis revealed that individuals carrying the A allele of rs1042044 had a higher risk of developing osteoporosis in the dominant model (P = 0.029, OR = 2.76, 95%CI: 1.09-6.99). Furthermore, a multiplicative interaction was found between rs1042044 and rs2268641 that was associated with osteoporosis in postmenopausal women (Pinteraction = 0.034). Importantly, this association remained independent of age, menopausal duration, family history of osteoporosis, and body mass index. However, no significant relationship was observed between GLP-1R haplotypes and PMOP. In conclusion, this study suggests a close association between the A allele on the GLP-1R rs1042044 and an increased risk of PMOP. Furthermore, this risk was significantly augmented by an SNP-SNP interaction with rs2268641. These results provide new scientific insights into the development of personalized prevention strategies and treatment approaches for PMOP.

Association between AXIN1 gene polymorphism (rs9921222) of WNT signaling pathway and susceptibility to osteoporosis in Egyptian patients: a case-control study

BACKGROUND

Osteoporosis (OP) is the most prevalent metabolic bone disease. Numerous genetic loci are strongly related to OP. AXIN1 is a significant gene that serves an important role in the WNT signaling pathway. The aim of this study was to explore the association between the AXIN1 genetic polymorphism (rs9921222) and OP susceptibility.

METHODS

A total of 101 subjects were enrolled in the study (50 patients with OP and 51 healthy individuals). Genomic DNA was extracted from whole blood using the QIAamp DNA Blood Mini Kit, and the AXIN1 gene polymorphism (rs9921222) was genotyped by TaqMan allelic discrimination assays. A logistic regression analysis was used to assess the association between genotypes and OP risk.

RESULTS

We found that AXIN1 rs9921222 had a significant association with the susceptibility of OP under the homozygote model (TT vs. CC: OR = 16.6, CI = 2.03-136.4, p = 0.009), (CT vs. CC: OR = 6.3, CI = 1.23-31.8, p = 0.027), recessive genetic model (TT vs.TC-CC: OR = 13.6, CI = 1.7-110.4, p = 0.015), and the dominant model (TT-TC vs. CC: OR = 9.7, CI = 2.6-36.3, p < 0.001). Allele T was significantly associated with OP risk (T vs. C: OR = 10.5, CI = 3.5-31.15, p = 0.001). There was a statistically significant difference between genotypes in mean platelet volume (p = 0.004), and platelet distribution width (p = 0.025). In addition, lumbar spine bone density, and femur neck bone density were significantly different between genotypes (p < 0.001).

CONCLUSION

AXIN1 rs9921222 was associated with OP susceptibility in the Egyptian population and should be considered a potential determinant risk for OP.

Ethnic disparities in fracture risk assessment using polygenic scores

Whether the PGS developed using data from European ancestry is predictive of fracture risk for minorities remains unclear. This study demonstrated that PGSs based on common BMD-related genetic variants discovered in the European ancestry cohort are predictive of fracture risk in people of Asian but not African ancestry.

PURPOSE

Large-scale genome-wide association studies (GWAS) on bone mineral density (BMD) have been conducted predominantly in European cohorts. Genetic models based on common variants associated with BMD have been evaluated using almost exclusively European data, which could potentially exacerbate health disparities due to different linkage disequilibrium among different ethnic groups.

METHODS

UK Biobank (UKB) is a large-scale population-based observational study starting in 2006 that recruited 502,617 individuals aged between 40 and 69 years with genotypic and phenotypic data available. Based on the summary statistics of two GWAS studies of femoral neck BMD and total body BMD, we derived four PGSs and assessed the association between each PGS and prevalent/incident fractures within each ethnic group separately using Multivariate logistic regressions and Cox proportional hazard models. All models were adjusted for age, sex, and the first four principal components.

RESULTS

We assessed four PGSs derived from European cohorts. Significant associations were observed between PGSs and fracture in European and Asian cohorts but not in the African cohort. Of all four PGSs, [Formula: see text] performed the best. A standard deviation decreases in [Formula: see text] were associated with an increased hazard ratio (HR) of 1.24 (1.22-1.27), 1.28 (0.83-1.99), and 1.34 (1.10-1.64) in European, African, and Asian ancestry, respectively. A low BMD-related PGS is associated with up to 2.35- and 4.31-fold increased fracture risk in European and Asian populations.

CONCLUSIONS

These results showed that PGSs based on common BMD-related genetic variants discovered in the European ancestry cohort are predictive of fracture risk in people of Asian but not African ancestry.

The clinical utility of the BMD-related comprehensive genome-wide polygenic score in identifying individuals with a high risk of osteoporotic fractures

The potential of bone mineral density (BMD)-related genome-wide polygenic score (PGS) in identifying individuals with a high risk of fractures remains unclear. This study suggests that an efficient PGS enables the identification of strata with up to a 1.5-fold difference in fracture incidence. Incorporating PGS into clinical diagnosis is anticipated to increase the population-level screening benefits.

PURPOSE

This study sought to construct genome-wide polygenic scores for femoral neck and total body BMD and to estimate their potential in identifying individuals with a high risk of osteoporotic fractures.

METHODS

Genome-wide polygenic scores were developed and validated for femoral neck and total body BMD. We externally tested the PGSs, both by themselves and in combination with available clinical risk factors, in 455,663 European ancestry individuals from the UK Biobank. The predictive accuracy of the developed genome-wide PGS was also compared with previously published restricted PGS employed in fracture risk assessment.

RESULTS

For each unit decrease in PGSs, the genome-wide PGSs were associated with up to 1.17-fold increased fracture risk. Out of four studied PGSs, [Formula: see text] (HR: 1.03; 95%CI 1.01-1.05, p = 0.001) had the weakest and the [Formula: see text] (HR: 1.17; 95%CI 1.15-1.19, p < 0.0001) had the strongest association with an incident fracture. In the reclassification analysis, compared to the FRAX base model, the models with [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] improved the reclassification of fracture by 1.2% (95% CI, 1.0 to 1.3%), 0.2% (95% CI, 0.1 to 0.3%), 1.4% (95% CI, 1.3 to 1.5%), and 2.2% (95% CI, 2.1 to 2.4%), respectively.

CONCLUSIONS

Our findings suggested that an efficient PGS estimate enables the identification of strata with up to a 1.7-fold difference in fracture incidence. Incorporating PGS information into clinical diagnosis is anticipated to increase the benefits of screening programs at the population level.

Frailty and genetic risk predict fracture after lung transplantation

Fractures negatively impact quality of life and survival. We hypothesized that recipient frailty score and genetic profile measured before transplant would predict risk of fracture after lung transplant. We conducted a retrospective cohort study of bone mineral density (BMD) and fracture among lung transplant recipients at a single center. The association between predictors and outcomes were assessed by multivariable time-dependent Cox models or regression analysis. Among the 284 participants, osteoporosis and fracture were highly prevalent. Approximately 59% of participants had posttransplant osteopenia, and 35% of participants developed at least 1 fracture. Low BMD was associated with a polygenic osteoporosis risk score, and the interaction between genetic score and BMD predicted fracture. Pretransplant frailty was associated with risk for spine and hip fracture, which were not associated with chronic lung allograft dysfunction or death. Chest fractures were the most frequent type of fracture and conferred a 2.2-fold increased risk of chronic lung allograft dysfunction or death (time-dependent P < .001). Pneumonia, pleural effusions, and acute rejection frequently occurred surrounding chest fracture. Pretransplant frailty and recipient genotype may aid clinical risk stratification for fracture after transplant. Fracture carries significant morbidity, underscoring the importance of surveillance and osteoporosis prevention.

Multiple polygenic scores improve bone mineral density prediction in an independent sample of Caucasian women

PURPOSE OF THE STUDY

To determine if multiple Genetic Risk Scores (GRSs) improve bone mineral density (BMD) prediction over single GRS in an independent sample of Caucasian women.

STUDY DESIGN

Based on summary statistics of four genome-wide association studies related to two osteoporosis-associated traits, namely BMD and heel quantitative ultrasound derived estimated BMD (eBMD), four GRSs were derived for 1205 individuals in the Genome-Wide Scan for Female Osteoporosis Gene Study. The effect of each GRS on BMD variation was assessed using multivariable linear regression, with conventional risk factors adjusted for. Next, the eBMD-related GRS that explained the most variance in BMD was selected to be entered into a multi-score model, along with the BMD-related GRS. Elastic net regularised regression was used to develop the multiscore model, which estimated the joint effect of two GRSs (GRS_BMD and GRS_eBMD) on BMD variation, after being adjusted for conventional risk factors.

RESULTS

With the same clinical risk factors having been adjusted for, the model that included GRS_BMD performed best by explaining 32.53% of the variance in BMD; the single-score model that included GRS_eBMD explained 34.03% of BMD variance. The model that includes both GRS_BMD and GRS_ eBMD, as well as the clinical risk factors, aggregately explained 35.05% in BMD variation. Compared with the single GRS models, the multiscore model explained significantly more variance in BMD.

CONCLUSIONS

The multipolygenic score model explained a considerable amount of BMD variation. Compared with single score models, multipolygenic score model provided significant improvement in explaining BMD variation.

GATA4 and estrogen receptor alpha bind at SNPs rs9921222 and rs10794639 to regulate AXIN1 expression in osteoblasts

Osteoporosis is a serious public health problem that affects 200 million people worldwide. Genome-wide association studies have revealed the association between several single nucleotide polymorphisms (SNPs) near WNT/β-catenin signaling genes and bone mineral density (BMD). The activation of β-catenin by WNT ligands is required for osteoblast differentiation. SNP rs9921222 is an intronic variant of AXIN1 (a scaffold protein in the destruction complex that regulates β-catenin signaling) that correlates with BMD. However, the biological mechanism of SNP rs9921222 has never been reported. Here, we show that the genotype of SNP rs9921222 correlates with the expression of AXIN1 in human osteoblasts. RNA and genomic DNA were analyzed from primary osteoblasts from 111 different individuals. Homozygous TT at rs9921222 correlates with a higher expression of AXIN1 than homozygous CC. Regional association analysis showed that rs9921222 is in high linkage disequilibrium (LD) with SNP rs10794639. In silico transcription factor analysis predicted that rs9921222 is within a GATA4 motif and rs10794639 is adjacent to an estrogen receptor alpha (ERα) motif. Mechanistically, GATA4 and ERα bind at SNPs rs9921222 and rs10794639 as detected by ChIP-qPCR. Luciferase assays demonstrate that rs9921222 is the causal SNP to alter ERα and GATA4 binding. GATA4 promoted the expression, and in contrast, ERα suppressed the expression of AXIN1 via the histone deacetylase complex member SIN3A. Functionally, the level of AXIN1 negatively correlates with the level of transcriptionally active β-catenin. In summary, we have discovered a molecular mechanism of the SNP rs9921222 to regulate AXIN1 through GATA4 and ERα binding in human osteoblasts.

The Polygenic and Monogenic Basis of Paediatric Fractures

PURPOSE OF REVIEW

Fractures are frequently encountered in paediatric practice. Although recurrent fractures in children usually unveil a monogenic syndrome, paediatric fracture risk could be shaped by the individual genetic background influencing the acquisition of bone mineral density, and therefore, the skeletal fragility as shown in adults. Here, we examine paediatric fractures from the perspective of monogenic and complex trait genetics.

RECENT FINDINGS

Large-scale genome-wide studies in children have identified ~44 genetic loci associated with fracture or bone traits whereas ~35 monogenic diseases characterized by paediatric fractures have been described. Genetic variation can predispose to paediatric fractures through monogenic risk variants with a large effect and polygenic risk involving many variants of small effects. Studying genetic factors influencing peak bone attainment might help in identifying individuals at higher risk of developing early-onset osteoporosis and discovering drug targets to be used as bone restorative pharmacotherapies to prevent, or even reverse, bone loss later in life.

Machine learning approaches for the prediction of bone mineral density by using genomic and phenotypic data of 5130 older men

The study aimed to utilize machine learning (ML) approaches and genomic data to develop a prediction model for bone mineral density (BMD) and identify the best modeling approach for BMD prediction. The genomic and phenotypic data of Osteoporotic Fractures in Men Study (n = 5130) was analyzed. Genetic risk score (GRS) was calculated from 1103 associated SNPs for each participant after a comprehensive genotype imputation. Data were normalized and divided into a training set (80%) and a validation set (20%) for analysis. Random forest, gradient boosting, neural network, and linear regression were used to develop BMD prediction models separately. Ten-fold cross-validation was used for hyper-parameters optimization. Mean square error and mean absolute error were used to assess model performance. When using GRS and phenotypic covariates as the predictors, all ML models' performance and linear regression in BMD prediction were similar. However, when replacing GRS with the 1103 individual SNPs in the model, ML models performed significantly better than linear regression (with lasso regularization), and the gradient boosting model performed the best. Our study suggested that ML models, especially gradient boosting, can improve BMD prediction in genomic data.

Opportunities and Challenges in Functional Genomics Research in Osteoporosis: Report From a Workshop Held by the Causes Working Group of the Osteoporosis and Bone Research Academy of the Royal Osteoporosis Society on October 5th 2020

The discovery that sclerostin is the defective protein underlying the rare heritable bone mass disorder, sclerosteosis, ultimately led to development of anti-sclerostin antibodies as a new treatment for osteoporosis. In the era of large scale GWAS, many additional genetic signals associated with bone mass and related traits have since been reported. However, how best to interrogate these signals in order to identify the underlying gene responsible for these genetic associations, a prerequisite for identifying drug targets for further treatments, remains a challenge. The resources available for supporting functional genomics research continues to expand, exemplified by "multi-omics" database resources, with improved availability of datasets derived from bone tissues. These databases provide information about potential molecular mediators such as mRNA expression, protein expression, and DNA methylation levels, which can be interrogated to map genetic signals to specific genes based on identification of causal pathways between the genetic signal and the phenotype being studied. Functional evaluation of potential causative genes has been facilitated by characterization of the "osteocyte signature", by broad phenotyping of knockout mice with deletions of over 7,000 genes, in which more detailed skeletal phenotyping is currently being undertaken, and by development of zebrafish as a highly efficient additional in vivo model for functional studies of the skeleton. Looking to the future, this expanding repertoire of tools offers the hope of accurately defining the major genetic signals which contribute to osteoporosis. This may in turn lead to the identification of additional therapeutic targets, and ultimately new treatments for osteoporosis.

USF3 modulates osteoporosis risk by targeting WNT16, RANKL, RUNX2, and two GWAS lead SNPs rs2908007 and rs4531631

Osteoporotic fractures cause major morbidity and mortality in the aging population. Genome-wide association studies (GWAS) have identified USF3 as the novel susceptibility gene of osteoporosis. However, the functional role in bone metabolism and the target gene of the basic helix-loop-helix transcription factor USF3 are unclear. Here, we show that USF3 enhances osteoblast differentiation and suppresses osteoclastogenesis in cultured human osteoblast-like U-2OS cells. Mechanistic studies revealed that transcription factor USF3 antagonistically interacts with anti-osteogenic TWIST1/TCF12 heterodimer in the WNT16 and RUNX2 promoter, and counteracts CREB1 and JUN/FOS in the RANKL promoter. Importantly, the osteoporosis GWAS variant g.1744A>G (rs2908007A>G) located in the WNT16 promoter confers G-allele-specific transcriptional modulation by USF3, TWIST1/TCF12 and TBX5/TBX15, and USF3 transactivates the osteoclastogenesis suppressor WNT16 promoter activity and antagonizes the repression of WNT16 by TWIST1 and TCF12. The risk G allele of osteoporosis GWAS variant g.3260A>G (rs4531631A>G) in the RANKL promoter facilitates the binding of CREB1 and JUN/FOS and enhances transactivation of the osteoclastogenesis contributor RANKL that is inhibited by USF3. Our findings uncovered the functional mechanisms of osteoporosis novel GWAS-associated gene USF3 and lead single nucleotide polymorphisms rs2908007 and rs4531631 in the regulation of bone formation and resorption.

Increased Burden of Common Risk Alleles in Children With a Significant Fracture History

Extreme presentations of common disease in children are often presumed to be of Mendelian etiology, but their polygenic basis has not been fully explored. We tested whether children with significant fracture history and no osteogenesis imperfecta (OI) are at increased polygenic risk for fracture. A childhood significant fracture history was defined as the presence of low-trauma vertebral fractures or multiple long bone fractures. We generated a polygenic score of heel ultrasound-derived speed of sound, termed "gSOS," which predicts risk of osteoporotic fracture. We tested if individuals from three cohorts with significant childhood fracture history had lower gSOS. A Canadian cohort included 94 children with suspected Mendelian osteoporosis, of which 68 had negative OI gene panel. Two Finnish cohorts included 59 children with significant fracture history and 22 with suspected Mendelian osteoporosis, among which 18 had no OI. After excluding individuals with OI and ancestral outliers, we generated gSOS estimates and compared their mean to that of a UK Biobank subset, representing the general population. The average gSOS across all three cohorts (n = 131) was -0.47 SD lower than that in UK Biobank (n = 80,027, p = 1.1 × 10^-5 ). The gSOS of 78 individuals with suspected Mendelian osteoporosis was even lower (-0.76 SD, p = 5.3 × 10^-10 ). Among the 131 individuals with a significant fracture history, we observed 8 individuals with gSOS below minus 2 SD from the mean; their mean lumbar spine DXA-derived bone mineral density Z-score was -1.7 (SD 0.8). In summary, children with significant fracture history but no OI have an increased burden of common risk alleles. This suggests that a polygenic contribution to disease should be considered in children with extreme presentations of fracture. © 2020 American Society for Bone and Mineral Research.

Identification of PIEZO1 polymorphisms for human bone mineral density

Bone mineral density (BMD) is a key indicator for diagnosis and treatment for osteoporosis; the reduction of BMD could increase the risk of osteoporotic fracture. It was very recently found that Piezo1 mediated mechanically evoked responses in bone and further participated in bone formation in mice. Here, we performed cross phenotype meta-analysis for human BMD at lumbar spine (LS), femoral neck (FN), distal radius/forearm (FA) and heel and screened out 14 top SNPs for PIEZO1, these SNPs were overlapped with putative enhancers, DNase-I hypersensitive sites and active promoter flanking regions. We found that the signal of the best SNP rs62048221 was mainly from heel ultrasound estimated BMD (-0.02 SD per T allele, P = 8.50E-09), where calcaneus supported most of the mechanical force of body when standing, walking and doing physical exercises. Each copy of the effect allele T of SNP rs62048221 was associated with a decrease of 0.0035 g/cm² BMD (P = 4.6E-27, SE = 0.0003) in UK Biobank data within 477,760 samples. SNP rs62048221 was located at the enhancer region (HEDD enhancer ID 2331049) of gene PIEZO1, site-directed ChIP assays in human mesenchymal stem cells (hMSCs) showed significant enrichment of H3K4me1 and H3K27ac in this region, luciferase assays showed that rs62048221 could significantly affect the activity of the enhancer where it resides. Our results first suggested that SNP rs62048221 might mediate the PIEZO1 expression level via modulating the activity of cis-regulatory elements and then further affect the BMD.

Osteoporosis genome-wide association study variant c.3781 C>A is regulated by a novel anti-osteogenic factor miR-345-5p

Upstream transcription factor family member 3 (USF3) c.3781C>A (rs1026364) in the 3'-untranslated region (3'-UTR) has been firmly associated with bone mineral density (BMD) in genome-wide association study (GWAS). However, the molecular mechanism by which it influences BMD and osteoporosis is unknown. Bioinformatics analyses suggested that the risk c.3781A allele creates a target site for hsa-miR-345-5p binding. Luciferase assay validated that the c.3781A allele displayed significantly lower luciferase activities than the c.3781C allele in the human osteoblast cell line hFOB1.19, osteosarcoma cell lines U-2OS and Saos-2, and embryonic kidney cell line 293T. Furthermore, hsa-miR-345-5p regulated USF3 expression on both messenger RNA and protein levels in hFOB1.19 and U937 cells with heterozygous A/C genotype. Transfection of hsa-miR-345-5p antagomiR in heterozygous hFOB1.19 cells significantly increased the expression of osteogenic marker genes RUNX2, OSTERIX, COL1A1, ALP, OPN, OCN, and alkaline phosphatase activity and matrix mineralization level. Importantly, we found that hsa-miR-345-5p also inhibits osteoblast maturation in cell lines U-2OS with hsa-miR-345-5p nonbinding C/C genotype by targeting RUNX3 and SMAD1. Our findings uncovered a novel pathogenetic mechanism of osteoporosis by GWAS variant c.3781C>A-mediated disruption of hsa-miR-345-5p binding at the 3'-UTR of USF3 and the functional role of hsa-miR-345-5p in osteogenic differentiation.

Evolutionary Perspectives on the Developing Skeleton and Implications for Lifelong Health

Osteoporosis is a significant cause of morbidity and mortality in contemporary populations. This common disease of aging results from a state of bone fragility that occurs with low bone mass and loss of bone quality. Osteoporosis is thought to have origins in childhood. During growth and development, there are rapid gains in bone dimensions, mass, and strength. Peak bone mass is attained in young adulthood, well after the cessation of linear growth, and is a major determinant of osteoporosis later in life. Here we discuss the evolutionary implications of osteoporosis as a disease with developmental origins that is shaped by the interaction among genes, behavior, health status, and the environment during the attainment of peak bone mass. Studies of contemporary populations show that growth, body composition, sexual maturation, physical activity, nutritional status, and dietary intake are determinants of childhood bone accretion, and provide context for interpreting bone strength and osteoporosis in skeletal populations. Studies of skeletal populations demonstrate the role of subsistence strategies, social context, and occupation in the development of skeletal strength. Comparisons of contemporary living populations and archeological skeletal populations suggest declines in bone density and strength that have been occurring since the Pleistocene. Aspects of western lifestyles carry implications for optimal peak bone mass attainment and lifelong skeletal health, from increased longevity to circumstances during development such as obesity and sedentism. In light of these considerations, osteoporosis is a disease of contemporary human evolution and evolutionary perspectives provide a key lens for interpreting the changing global patterns of osteoporosis in human health.

Use of Mendelian Randomization to Examine Causal Inference in Osteoporosis

Epidemiological studies have identified many risk factors for osteoporosis, however it is unclear whether these observational associations reflect true causal effects, or the effects of latent confounding or reverse causality. Mendelian randomization (MR) enables causal relationships to be evaluated, by examining the relationship between genetic susceptibility to the risk factor in question, and the disease outcome of interest. This has been facilitated by the development of two-sample MR analysis, where the exposure and outcome are measured in different studies, and by exploiting summary result statistics from large well-powered genome-wide association studies that are available for thousands of traits. Though MR has several inherent limitations, the field is rapidly evolving and at least 14 methodological extensions have been developed to overcome these. The present paper aims to discuss some of the limitations in the MR analytical framework, and how this method has been applied to the osteoporosis field, helping to reinforce conclusions about causality, and discovering potential new regulatory pathways, exemplified by our recent MR study of sclerostin.

Influence of Estrogen Receptor Alpha Polymorphism on Bone Mineral Density in Iranian Children

BACKGROUND

Bone mass acquisition in childhood is directly linked to adult bone mineral density (BMD) and fracture risk. BMD is a heritable trait, more than 70% of its variability among a population is affected by genetic factors.

OBJECTIVES

In the present study, we wanted to investigate the association between estrogen receptor alpha (ESR1) polymorphisms, PvuII (rs2234693) and XbaI (rs9340799), and bone area, bone mineral content (BMC), and BMD of the lumbar spine, femoral neck, and also of the total body less the head in Iranian children.

METHODS

The ESR1 gene PvuII and XbaI genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism. Bone area, BMC, BMD, and bone mineral apparent density (BMAD) were assessed by dual-energy X-ray absorptiometry (DEXA). Linear regression was carried out to examine the effects of the ESR1 (PvuII and XbaI) polymorphisms on DEXA outputs when adjusted for confounding factors (i.e., age, sex, BMI, and pubertal stage) in 3 models.

RESULTS

ESR1 (PvuII) gene polymorphisms (CT vs. CC) showed significant effects on the BMC of the total body less the head in all 3 models. For ESR1 (XbaI), individuals with the AG genotype had higher lumbar spine BMD and lumbar spine BMAD compared to other genotypes.

CONCLUSIONS

It seems that the PvuII and XbaI polymorphisms of ESR1 could be associated with BMC and BMD variation in Iranian children and adolescents.

Association Between Age at Puberty and Bone Accrual From 10 to 25 Years of Age

Importance

Bone health in early life is thought to influence the risk of osteoporosis in later life.

Objective

To examine whether puberty timing is associated with bone mineral density accrual up to adulthood.

Design, Setting, and Participants

This cohort study used data from the Avon Longitudinal Study of Parents and Children, a prospective population-based birth cohort initiated in 1991 to 1992 in southwest England. The participants were 6389 healthy British people who underwent regular follow-up, including up to 6 repeated bone density scans from ages 10 to 25 years. Data analysis was performed from June 2018 to June 2019.

Exposures

Age at puberty from estimated age at peak height velocity (years).

Main Outcomes and Measures

Gains per year in whole-body bone mineral density (grams per square centimeter), assessed by dual-energy x-ray absorptiometry at ages 10, 12, 14, 16, 18, and 25 years and modeled using linear splines.

Results

A total of 6389 participants (3196 [50.0%] female) were included. The mean (SD) age at peak height velocity was 13.5 (0.9) years for male participants and 11.6 (0.8) years for female participants. Male participants gained bone mineral density at faster rates than did female participants, with the greatest gains in both male participants (0.139 g/cm2/y; 95% CI, 0.127-0.151 g/cm2/y) and female participants (0.106 g/cm2/y; 95% CI, 0.098-0.114 g/cm2/y) observed between the year before and 2 years after peak height velocity. When aligned by chronological age, per 1-year older age at puberty was associated with faster subsequent gains in bone mineral density; the magnitudes of faster gains were greatest between ages 14 and 16 years in both male participants (0.013 g/cm2/y; 95% CI, 0.011-0.015 g/cm2/y) and female participants (0.014 g/cm2/y; 95% CI, 0.014-0.015 g/cm2/y), were greater in male participants (0.011 g/cm2/y; 95% CI, 0.010-0.013 g/cm2/y) than in female participants (0.003 g/cm2/y; 95% CI, 0.003-0.004 g/cm2/y) between ages 16 and 18 years, and were least in both male participants (0.002 g/cm2/y; 95% CI, 0.001-0.003 g/cm2/y) and female participants (0.000 g/cm2/y; 95% CI, -0.001 to 0.000 g/cm2/y) between ages 18 and 25 years. Despite faster gains, older age at puberty was associated with persistently lower bone mineral density, changing from 0.050 g/cm2 (95% CI, -0.056 to -0.045 g/cm2) lower at age 14 years to 0.047 g/cm2 (95% CI, -0.051 to -0.043 g/cm2) lower at age 25 years in male participants and from 0.044 g/cm2 (95% CI, -0.046 to -0.041 g/cm2) to 0.034 g/cm2 (95% CI, -0.036 to -0.032 g/cm2) lower at the same ages in female participants.

Conclusions and Relevance

People with older pubertal age should be advised on how to maximize bone mineral density and minimize its decrease in later life to help prevent fracture and osteoporosis.

LncRNA ZBTB40-IT1 modulated by osteoporosis GWAS risk SNPs suppresses osteogenesis

Previous genome-wide linkage and association studies have identified an osteoporosis-associated locus at 1p36 that harbors SNPs rs34920465 and rs6426749. The 1p36 locus also comprises the WNT4 gene with known role in bone metabolism and functionally unknown ZBTB40/lncRNA ZBTB40-IT1 genes. How these might interact to contribute to osteoporosis susceptibility is not known. In this study, we show that lncRNA ZBTB40-IT1 is able to suppress osteogenesis and promote osteoclastogenesis by regulating the expression of WNT4, RUNX2, OSX, ALP, COL1A1, OPG and RANKL in U-2OS and hFOB1.19 cell lines, whereas ZBTB40 plays an opposite role in bone metabolism. Treatment with parathyroid hormone significantly downregulates the expression of ZBTB40-IT1 in U-2OS cell lines. ZBTB40 can suppress ZBTB40-IT1 expression but has no response to parathyroid hormone treatment. Dual-luciferase assay and biotin pull-down assay demonstrate that osteoporosis GWAS lead SNPs rs34920465-G and rs6426749-C alleles can respectively bind transcription factors JUN::FOS and CREB1, and upregulate ZBTB40 and ZBTB40-IT1 expression. Our study discovers the critical role of ZBTB40 and lncRNA ZBTB40-IT1 in bone metabolism, and provides a mechanistic basis for osteoporosis GWAS lead SNPs rs34920465 and rs6426749.

Identification of pleiotropic genetic variants affecting osteoporosis risk in a Korean elderly cohort

Pleiotropy has important implications for understanding the genetic basis and risk assessment of osteoporosis. Our aim was to identify pleiotropic genetic variants associated with the development of osteoporosis and predict osteoporosis risk by leveraging pleiotropic variants. We evaluated the effects of 21 conventional risk factors and 185 single-nucleotide polymorphisms (SNPs) in 63 inflammation- and metabolism-related genes on osteoporosis risk in a community-based Korean cohort study of 1025 participants, the Hallym Aging Study. Ten nongenetic factors, including sex (female) and hematocrit level, and 12 SNPs across ten genes showed evidence of association with incident osteoporosis in 270 initially osteoporosis-free subjects who completed a 6-year follow up. Three gene variants, rs1801282 (PPARG-Pro12Ala, hazard ratio (HR) = 3.26, P = 0.008), rs1408282 (near EPHA7, HR = 1.87, P = 0.002), and rs2076212 (PNPLA3-Gly115Cys, HR = 2.24, P = 0.024), were associated with significant differences in survival among the three genotype groups (P_diff = 0.042, 0.003, and 0.048, respectively). Individuals in the highest polygenic risk score tertile were 27.9 fold more likely to develop osteoporosis than those in the lowest tertile (P = 0.004). The PPARG gene in particular was a hub pleiotropic gene in the epistasis network. Our findings highlight pleiotropic modulations of metabolism- and inflammation-related genes in the development of osteoporosis and demonstrate the contribution of pleiotropic genetic variants in prediction of osteoporosis risk.

Genetic profiling of decreased bone mineral density in an independent sample of Caucasian women

Genetic risk of low bone mineral density in women remains unclear. This study found that a large percentage of Caucasian women have a high genetic risk of osteoporosis, and genetic risk scores are significantly associated with BMD variation in a bone healthy sample of Caucasian women.

INTRODUCTION

We aimed to examine the distribution of risk alleles in an independent sample and to determine if such genetic components are associated with bone mineral density (BMD) variation in the sample.

METHODS

Existing genotype data of 1205 women in the cross-sectional Genomic Wide Scans for Female Osteoporosis Gene Study (GWSFO) were analyzed. Multi-loci genetic risk scores (GRSs) based on 62 BMD-associated single nucleotide polymorphisms (SNPs) were calculated. Regression analysis was employed to assess the association between GRSs and BMD. To examine the effect of SNPs clustered within key pathways associated with the development of osteoporosis, subtype weighted GRS specific to WNT signaling (6 SNPs), RANK-RANKL-OPG (3 SNPs), and mesenchymal stem differentiation (3 SNPs) were generated for analysis.

RESULTS

The unweighted GRS ranged from 48 to 80. One third of the women carried 66% risk alleles. After adjusting for age, height, and body weight, each unit increase of weighted GRS was associated with a decrease in BMD of 0.097 at femur (p < 0.0001) and 0.110 (p < 0.0001) at lumbar spine. The weighted GRS accounted for only 3.17-4.52% of BMD variance. The WNT signaling pathway GRS (6 SNPs) and the RANK-RANKL-OPG signaling pathway GRS (3 SNPs) both were significantly associated with decreased BMD at femur neck (p = 0.0004 and p = 0.0063, respectively) and lumbar spine (p < 0.0001 and p = 0.0001, respectively), while the mesenchymal stem cell differentiation pathway (3 SNPs) GRSs were associated only with the lumbar spine BMD (p = 0.045).

CONCLUSIONS

A substantially large percentage of healthy Caucasian women have a high genetic risk of osteoporosis. Weighted GRS was significantly associated with decreased BMD. The contribution of subtype GRS to the BMD variation differs by specific biological pathway and skeletal regions.

The RSPO3 gene as genetic markers for bone mass assessed by quantitative ultrasound in a population of young adults

Ultrasound bone mass measurement has been postulated as a valuable bone-health assessment tool for primary care. The aim of this study was to analyse the possible relationship between the SPTBN1, RSPO3, CCDC170, DKK1, GPATCH1, and TMEM135 genes, with calcaneal quantitative ultrasound (QUS) in a population of young adults. These genes were first associated with broadband ultrasound attenuation (BUA) in the GEFOS/GENOMOS study. A cross-sectional study was conducted on 575 individuals (mean age 20.41 ± 2.69). Bone mass at the right calcaneus was estimated by QUS. Six single-nucleotide polymorphisms (SNPs) in SPTBN1 (rs11898505), RSPO3 (rs7741021), CCDC170 (rs4869739), DKK1 (rs7902708), TMEM135 (rs597319), and GPATCH1 (rs10416265) were selected as genetic markers based on their previous association with calcaneal QUS. After adjusting for multiple confounding factors, the only significant association with QUS in our population was found for the rs7741021 SNP in the RSPO3 gene (P = 0.006) using the dominant model of inheritance. This suggests the possible implication of the RSPO3 gene in bone mass acquisition during early adulthood.

Exome-wide association study identifies genetic polymorphisms of C12orf51, MYL2, and ALDH2 associated with blood lead levels in the general Korean population

BACKGROUND

Lead (Pb) is a ubiquitous toxic metal present in the environment that poses adverse health effects to humans. Inter-individual variation in blood Pb levels is affected by various factors, including genetic makeup. However, limited data are available on the association between genetic variation and blood Pb levels. The purpose of this study was to identify the genetic markers associated with blood Pb levels in the Korean population.

METHODS

The study subjects consisted of 1,483 healthy adults with no history of occupational exposure to Pb. We measured blood Pb levels and calculated probable daily intake of Pb according to dietary data collected using 24-hour recall. We conducted exome-wide association screening using Illumina Human Exome-12v1.2 platform (n = 500) and a replication analysis using VeraCode Goldengate assay (n = 1,483).

RESULTS

Among the 244,770 single nucleotide polymorphisms (SNPs) tested, 12 SNPs associated with blood Pb level were identified, with suggestive significance level (P < 1 × 10^-4). In the Goldengate assay for replication, three SNPs (C12orf51 rs11066280, MYL2 rs12229654, and ALDH2 rs671) were associated with statistically suggestively significant differences in blood Pb levels. When stratified by drinking status, a potential association of C12orf51 rs11066280, MYL2 rs12229654, and ALDH2 rs671 with blood Pb level was observed only in drinkers. A marginally significant gene-environment interaction between ALDH2 rs671 and alcohol consumption was observed in relation to blood Pb levels. The effects of the three suggestively significant SNPs on blood Pb levels was dependent on daily calcium intake amounts.

CONCLUSIONS

This exome-wide association study indicated that C12orf51 rs11066280, MYL2 rs12229654, and ALDH2 rs671 polymorphisms are linked to blood Pb levels in the Korean population. Our results suggest that these three SNPs are involved in the determination of Pb levels in Koreans via the regulation of alcohol drinking behavior, and that their negative effects may be compensated by appropriate calcium intake.

Genetics of pediatric bone strength

Osteoporosis is one of the most common chronic forms of disability in postmenopausal women and represents a major health burden around the world. Bone fragility is affected by bone mineral density (BMD), and, one of the most important factors in preventing osteoporosis is optimizing peak bone mass, which is achieved during growth in childhood and adolescence. BMD is a complex trait resulting from environmental and genetic factors. Genome-wide association studies have discovered robust genetic signals influencing BMD in adults, and similar studies have also been conducted to investigate the genetics of BMD in the pediatric setting. These latter studies have revealed that many adult osteoporosis-related loci also regulate BMD during growth. These investigations have the potential to profoundly impact public health and will allow for the eventual development of effective interventions for the prevention of osteoporosis.

The case for genome-wide association studies of bone acquisition in paediatric and adolescent populations

Peak bone mass, the maximum amount of bone accrued at the end of the growth period, is an important predictor of future risk of osteoporosis and fracture. Hence, the contribution of genetic factors influencing bone accrual is of considerable interest to the osteoporosis research community. In this article, we review evidence that genetic factors play an important role in bone growth, describe the genetic loci implicated so far and briefly discuss lessons learned from the application of genome-wide association studies. Moreover, we attempt to make the case for genetic investigations of bone mineral density in paediatric and young adult populations, describing their potential to increase our knowledge of the process of bone metabolism throughout the life course, and in turn, identify novel targets for the pharmacological treatment of osteoporosis.

Genetic Risk Scores Implicated in Adult Bone Fragility Associate With Pediatric Bone Density

Using adult identified bone mineral density (BMD) loci, we calculated genetic risk scores (GRS) to determine if they were associated with changes in BMD during childhood. Longitudinal data from the Bone Mineral Density in Childhood Study were analyzed (N = 798, 54% female, all European ancestry). Participants had up to 6 annual dual energy X-ray scans, from which areal BMD (aBMD) Z-scores for the spine, total hip, and femoral neck were estimated, as well as total body less head bone mineral content (TBLH-BMC) Z-scores. Sixty-three single-nucleotide polymorphisms (SNPs) were genotyped, and the percentage of BMD-lowering alleles carried was calculated (overall adult GRS). Subtype GRS that include SNPs associated with fracture risk, pediatric BMD, WNT signaling, RANK-RANKL-OPG, and mesenchymal stem cell differentiation were also calculated. Linear mixed effects models were used to test associations between each GRS and bone Z-scores, and if any association differed by sex and/or chronological age. The overall adult, fracture, and WNT signaling GRS were associated with lower Z-scores (eg, spine aBMD Z-score: βadult  = -0.04, p = 3.4 × 10(-7) ; βfracture = -0.02, p = 8.9 × 10(-6) ; βWNT  = -0.01, p = 3.9 × 10(-4) ). The overall adult GRS was more strongly associated with lower Z-scores in females (p-interaction ≤ 0.05 for all sites). The fracture GRS was more strongly associated with lower Z-scores with increasing age (p-interaction ≤ 0.05 for all sites). The WNT GRS associations remained consistent for both sexes and all ages (p-interaction > 0.05 for all sites). The RANK-RANKL-OPG GRS was more strongly associated in females with increasing age (p-interaction < 0.05 for all sites). The mesenchymal stem cell GRS was associated with lower total hip and femoral neck Z-scores, in both boys and girls, across all ages. No associations were observed between the pediatric GRS and bone Z-scores. In conclusion, adult identified BMD loci associated with BMD and BMC in the pediatric setting, especially in females and in loci involved in fracture risk and WNT signaling.