Maria Nethander

Osteoporotic fractures are a major global health burden. To uncover potential targets for fracture prevention, we use a proteome-wide Mendelian randomization (MR) approach combined with colocalization. Here we show that nine circulating proteins associate with forearm fracture risk, including sclerostin and osteoprotegerin targeted by existing osteoporosis treatments, and three other known bone-related proteins, providing proof of concept for our MRpipeline. Notably, we identify ephrin-A1 as a novel protective factor against fractures, a membrane-linked protein partly released into circulation that binds its high-affinity receptor EphA2 on osteoblasts. Experimental models and genetic analyses indicate that ephrin-A1 increases bone mineral density, supporting a mechanism by which this pathway may mediate fracture protection. Spatial expression analysis with the innovative 3D DeepBone technique suggests ephrin-A1 on endothelial cells interacts with EphA2 on adjacent osteoblasts at the bone surface. These findings position ephrin-A1–EphA2 signalling as a therapeutic target to strengthen bone and reduce fracture risk.

Despite the importance of the gut microbiome to health, the role of human genetic variation in shaping its composition remains poorly understood. Here we report genome-wide association analyses of harmonized metagenomic data from 16,017 adults in four Swedish population-based studies, with replication in 12,652 people from the Norwegian HUNT study. We identified variants in the OR51E1–OR51E2 locus, encoding sensors for microbiome-derived fatty acids, associated with microbial richness. We further identified 15 study-wide significant genetic associations ( P < 5.4 × 10 ⁻¹¹ ) involving eight loci and 14 common bacterial species, of which 11 associations at six loci were replicated. The results confirm previously reported associations at LCT , ABO and FUT2 , and provide evidence for new loci MUC12 , CORO7–HMOX2 , SLC5A11 , FOXP1 and FUT3–FUT6 , with supporting data from metabolomics and gene expression analyses. Our findings link gut microbial variation genetically to gastrointestinal functions, including enteroendocrine fatty acid sensing, bile composition and mucosal layer composition.

The gut microbiota is associated with human health and disease. Here we conducted a genome-wide association study of host genetic factors influencing gut microbiota composition in 12,652 individuals from the Trøndelag Health Study (HUNT), with replication in Nordic cohorts ( n = 16,017–21,976). We identified 12 reproducible SNP–species associations across six genomic loci, including known ( LCT , ABO ) and novel ( HLA-DQB1 , MUC12 , SLC37A2 , FUT2 ) regions. Additionally, we detected genetic signals associated with gut microbiota functional modules at three loci ( LCT , ABO , FUT2 ). Follow-up analyses suggest that these host–microbiota associations are linked to the pathogenesis of celiac disease and hemorrhoidal disease. Mendelian randomization analyses provided evidence supporting a causal effect of body mass index on gut microbiota composition. These findings highlight the interplay between host genetics and gut microbiota for human health and disease.

The effects of androgens on women’s bone health are not fully understood. Mendelian randomization (MR) studies using sex-combined data suggest that sex hormone-binding globulin (SHBG) and bioavailable testosterone (BioT) causally affect bone traits. Given significant sex differences in hormone regulation and effects, female-specific MR studies are necessary. In the current study, we explored the causal relationships of SHBG, BioT, and total testosterone (TT) with forearm fracture (FAFx) risk in women using two-sample MR analyses. We utilized a unique female-specific FAFx outcome dataset from three European biobanks (UFO, HUNT, Estonian Biobank) comprising 111,351 women and 8823 FAFx cases, along with female-specific genetic instruments of SHBG, BioT, and TT identified in the UK Biobank. We also assessed bone mineral density (BMD) at the forearm (FA), femoral neck (FN), and lumbar spine (LS) using female-specific GWAS data from the GEFOS consortium. High SHBG (odds ratio per standard deviation increase (OR/SD): 1.53, 95% confidence intervals (CIs): 1.34–1.75), low BioT (OR/SD: 0.77, 0.71–0.84) and low TT (OR/SD 0.90, 0.83–0.98) were causally associated with increased FAFx risk. BioT was positively, and SHBG inversely, causally associated with especially FA-BMD, but also LS-BMD and FN-BMD, while TT was only significantly positively associated with FA-BMD and LS-BMD. We propose that endogenous androgens and SHBG are important for women’s bone health at distal trabecular-rich bone sites such as the distal forearm and may serve as predictors for FAFx risk.

Context As men age, circulating testosterone (T) decreases, circulating sex-hormone binding globulin (SHBG) increases, and risk of fracture increases. It is unclear if circulating T, independently of comorbidities, is associated with fracture risk in men. Objectives To determine associations for T and SHBG with incident fractures in men. Methods We utilized the large (n=205,973 participants, 11,088 any fracture cases, 1,680 hip fracture cases, 1,366 forearm fracture cases) and well-characterized UK Biobank cohort. Associations were modelled using Cox regressions, adjusting for multiple comorbidities/covariates, imputing for missing information, and assessing non-linearity using cubic splines. Results For T, not considering SHBG, there was a non-linear association with hip but not forearm fractures, with the lowest risk in the second quintile. However, in models adjusted for SHBG or using calculated free T, lower T was associated with higher risk for fractures at all evaluated bone sites. Lower SHBG was strongly associated with lower risk of hip and forearm fractures (Q1 vs Q5, hip 0.55, 0.47–0.65; forearm 0.62, 0.52–0.74). Conclusion Low circulating SHBG is strongly associated with low risk of fracture at all evaluated bone sites, while the associations of circulating T with fracture risk are of lesser magnitude, non-linear, inconsistent among fracture site, and affected by adjustment for SHBG. These findings demonstrate that circulating SHBG, rather than T, is a major independent biomarker of fracture risk in men. Consequently, both total T and SHBG should be assessed when examining the relationship of endogenous T concentrations with fractures in middle-aged to older men.

As there are effective treatments to reduce hip fractures, identification of patients at high risk of hip fracture is important to inform efficient intervention strategies. To obtain a new tool for hip fracture prediction, we developed a protein-based risk score in the Cardiovascular Health Study using an aptamer-based proteomic platform. The proteomic risk score predicted incident hip fractures and improved hip fracture discrimination in two Trøndelag Health Study validation cohorts using the same aptamer-based platform. When transferred to an antibody-based proteomic platform in a UK Biobank validation cohort, the proteomic risk score was strongly associated with hip fractures (hazard ratio per s.d. increase, 1.64; 95% confidence interval 1.53–1.77). The proteomic risk score, but not available polygenic risk scores for fractures or bone mineral density, improved the C-index beyond the fracture risk assessment tool (FRAX), which integrates information from clinical risk factors (C-index, FRAX 0.735 versus FRAX + proteomic risk score 0.776). The developed proteomic risk score constitutes a new tool for stratifying patients according to hip fracture risk; however, its improvement in hip fracture discrimination is modest and its clinical utility beyond FRAX with information on femoral neck bone mineral density remains to be determined.

Femoral neck width (FNW) derived from DXA scans may provide a useful adjunct to hip fracture prediction. Therefore, we investigated whether FNW is related to hip fracture risk independently of femoral neck bone mineral density (FN-BMD), using a genetic approach. FNW was derived from points automatically placed on the proximal femur using hip DXA scans from 38 150 individuals (mean age 63.8 yr, 48.0% males) in UK Biobank (UKB). Genome-wide association study (GWAS) identified 71 independent genome-wide significant FNW SNPs, comprising genes involved in cartilage differentiation, hedgehog, skeletal development, in contrast to SNPs identified by FN-BMD GWAS which primarily comprised runx1/Wnt signaling genes (MAGMA gene set analyses). FNW and FN-BMD SNPs were used to generate genetic instruments for multivariable Mendelian randomization. Greater genetically determined FNW increased risk of all hip fractures (odds ratio [OR] 1.53; 95% CI, 1.29–1.82 per SD increase) and femoral neck fractures (OR 1.58;1.30–1.92), but not trochanteric or forearm fractures. In contrast, greater genetically determined FN-BMD decreased fracture risk at all 4 sites. FNW and FN-BMD SNPs were also used to generate genetic risk scores (GRSs), which were examined in relation to incident hip fracture in UKB (excluding the FNW GWAS population; n = 338 742, 3222 cases) using a Cox proportional hazards model. FNW GRS was associated with increased risk of all incident hip fractures (HR 1.08;1.05–1.12) and femoral neck fractures (hazard ratio [HR] 1.10;1.06–1.15), but not trochanteric fractures, whereas FN-BMD GRS was associated with reduced risk of all hip fracture types. We conclude that the underlying biology regulating FNW and FN-BMD differs, and that DXA-derived FNW is causally related to hip fractures independently of FN-BMD, adding information beyond FN-BMD for hip fracture prediction. Hence, FNW derived from DXA analyses or a FNW GRS may contribute clinically useful information beyond FN-BMD for hip fracture prediction. Femoral neck width (FNW) derived from DXA scans may provide useful information about hip fracture prediction, over and above that provided by BMD measurements. Therefore, we investigated whether FNW is related to hip fracture risk independently of BMD, using a genetic approach. FNW was derived from points automatically placed on the hip in DXA scans obtained from 38 150 individuals (mean age 63.8 yr, 48.0% males) in UK Biobank. Seventy-one distinct genetic factors were found to be associated with FNW. Individuals who were predicted by their genes to have greater FNW had a higher risk of hip but not forearm fractures. In contrast, those with greater genetically determined BMD of the femoral neck had a lower risk of both hip and forearm fractures. We conclude that the underlying biology regulating FNW and BMD of the femoral neck differs, and that FNW derived from DXA analyses may contribute clinically useful information beyond BMD for hip fracture prediction.

Osteoporotic fracture is among the most common and costly of diseases. While reasonably heritable, its genetic determinants have remained elusive. Forearm fractures are the most common clinically recognized osteoporotic fractures with a relatively high heritability. To establish an atlas of the genetic determinants of forearm fractures, we performed genome-wide association analyses including 100,026 forearm fracture cases. We identified 43 loci, including 26 new fracture loci. Although most fracture loci associated with bone mineral density, we also identified loci that primarily regulate bone quality parameters. Functional studies of one such locus, at TAC4, revealed that Tac4^–/– mice have reduced mechanical bone strength. The strongest forearm fracture signal, at WNT16, displayed remarkable bone-site-specificity with no association with hip fractures. Tall stature and low body mass index were identified as new causal risk factors for fractures. The insights from this atlas may improve fracture prediction and enable therapeutic development to prevent fractures.

Resting heart rate is associated with cardiovascular diseases and mortality in observational and Mendelian randomization studies. The aims of this study are to extend the number of resting heart rate associated genetic variants and to obtain further insights in resting heart rate biology and its clinical consequences. A genome-wide meta-analysis of 100 studies in up to 835,465 individuals reveals 493 independent genetic variants in 352 loci, including 68 genetic variants outside previously identified resting heart rate associated loci. We prioritize 670 genes and in silico annotations point to their enrichment in cardiomyocytes and provide insights in their ECG signature. Two-sample Mendelian randomization analyses indicate that higher genetically predicted resting heart rate increases risk of dilated cardiomyopathy, but decreases risk of developing atrial fibrillation, ischemic stroke, and cardio-embolic stroke. We do not find evidence for a linear or non-linear genetic association between resting heart rate and all-cause mortality in contrast to our previous Mendelian randomization study. Systematic alteration of key differences between the current and previous Mendelian randomization study indicates that the most likely cause of the discrepancy between these studies arises from false positive findings in previous one-sample MR analyses caused by weak-instrument bias at lower P-value thresholds. The results extend our understanding of resting heart rate biology and give additional insights in its role in cardiovascular disease development.