Causal associations of iron status with gout and rheumatoid arthritis, but not with inflammatory bowel disease

Elucidating the role of liver enzymes as markers and regulators in ovarian cancer: a synergistic approach using Mendelian randomization, single-cell analysis, and clinical evidence

OBJECTIVE

To investigate the association between liver enzymes and ovarian cancer (OC), and to validate their potential as biomarkers and their mechanisms in OC. Methods Genome-wide association studies for OC and levels of enzymes such as Alkaline phosphatase (ALP), Aspartate aminotransferase (AST), Alanine aminotransferase, and gamma-glutamyltransferase were analyzed. Univariate and multivariate Mendelian randomization (MR), complemented by the Steiger test, identified enzymes with a potential causal relationship to OC. Single-cell transcriptomics from the GSE130000 dataset pinpointed pivotal cellular clusters, enabling further examination of enzyme-encoding gene expression. Transcription factors (TFs) governing these genes were predicted to construct TF-mRNA networks. Additionally, liver enzyme levels were retrospectively analyzed in healthy individuals and OC patients, alongside the evaluation of correlations with cancer antigen 125 (CA125) and Human Epididymis Protein 4 (HE4).

RESULTS

A total of 283 single nucleotide polymorphisms (SNPs) and 209 SNPs related to ALP and AST, respectively. Using the inverse-variance weighted method, univariate MR (UVMR) analysis revealed that ALP (P = 0.050, OR = 0.938) and AST (P = 0.017, OR = 0.906) were inversely associated with OC risk, suggesting their roles as protective factors. Multivariate MR (MVMR) confirmed the causal effect of ALP (P = 0.005, OR = 0.938) on OC without reverse causality. Key cellular clusters including T cells, ovarian cells, endothelial cells, macrophages, cancer-associated fibroblasts (CAFs), and epithelial cells were identified, with epithelial cells showing high expression of genes encoding AST and ALP. Notably, TFs such as TCE4 were implicated in the regulation of GOT2 and ALPL genes. OC patient samples exhibited decreased ALP levels in both blood and tumor tissues, with a negative correlation between ALP and CA125 levels observed.

CONCLUSION

This study has established a causal link between AST and ALP with OC, identifying them as protective factors. The increased expression of the genes encoding these enzymes in epithelial cells provides a theoretical basis for developing novel disease markers and targeted therapies for OC.

Iron metabolism and arthritis: Exploring connections and therapeutic avenues

ABSTRACT

Iron is indispensable for the viablility of nearly all living organisms, and it is imperative for cells, tissues, and organisms to acquire this essential metal sufficiently and maintain its metabolic stability for survival. Disruption of iron homeostasis can lead to the development of various diseases. There is a robust connection between iron metabolism and infection, immunity, inflammation, and aging, suggesting that disorders in iron metabolism may contribute to the pathogenesis of arthritis. Numerous studies have focused on the significant role of iron metabolism in the development of arthritis and its potential for targeted drug therapy. Targeting iron metabolism offers a promising approach for individualized treatment of arthritis. Therefore, this review aimed to investigate the mechanisms by which the body maintains iron metabolism and the impacts of iron and iron metabolism disorders on arthritis. Furthermore, this review aimed to identify potential therapeutic targets and active substances related to iron metabolism, which could provide promising research directions in this field.

Heart failure potentially affects the cortical structure of the brain

BACKGROUND

Heart failure (HF) has been reported to affect cerebral cortex structure, but the underlying cause has not been determined. This study used Mendelian randomization (MR) to reveal the causal relationship between HF and structural changes in the cerebral cortex.

METHODS

HF was defined as the exposure variable, and cerebral cortex structure was defined as the outcome variable. Inverse-variance weighted (IVW), MR-Egger regression and weighted median (WME) were performed for MR analysis; MR-PRESSO and Egger's intercept was used to test horizontal pleiotropy; and "leave-one-out" was used for sensitivity analysis.

RESULTS

Fifty-two single nucleotide polymorphisms (SNPs) were defined as instrumental variables (IVs), and there was no horizontal pleiotropy in the IVs. According to the IVW analysis, the OR and 95% CI of cerebral cortex thickness were 0.9932 (0.9868-1.00) (P=0.0402), and the MR-Egger intercept was -15.6× 10-5 (P = 0.7974) and the Global test pval was 0.078. The P-value of the cerebral cortex surface was 0.2205, and the MR-Egger intercept was -34.69052 (P= 0.6984) and the Global Test pval was 0.045. HF had a causal effect on the surface area of the caudal middle frontal lobule (P=0.009), insula lobule (P=0.01), precuneus lobule (P=0.049) and superior parietal lobule (P=0.044).

CONCLUSIONS

HF was potentially associated with changes in cortical thickness and in the surface area of the caudal middle frontal lobule, insula lobule, precuneus lobule and superior parietal lobule.

Exploring the causal associations of micronutrients on urate levels and the risk of gout: A Mendelian randomization study

BACKGROUND & AIMS

Growing evidence has indicated a potential association between micronutrient levels, urate levels, and the risk of gout. However, the causal association underlying these associations still remains uncertain. Previous observational studies and randomized controlled trials investigating the association between micronutrients, urate levels, and the risk of gout have been limited in their scope and depth. The aim of this study was to utilize Mendelian randomization (MR) to investigate the causal associations between genetically predicted micronutrient levels, urate levels, and the risk of gout.

METHODS

In this study, we conducted a comprehensive examination of 10 specific micronutrients (vitamin B6, vitamin B12, vitamin C, vitamin D, folate, calcium, iron, copper, zinc, and selenium) as potential exposures. Two-sample MR analyses were performed to explore their causal associations with urate levels and the risk of gout. In these analyses, gout data were collected from the Global Biobank Meta-Analysis Initiative (N = 1,069,839, N cases = 30,549) and urate levels data from CKDGen Consortium (N = 288,649) by utilizing publicly available summary statistics from independent cohorts of European ancestry. We performed inverse-variance weighted MR analyses as main analyses, along with a range of sensitivity analyses, such as MR-Egger, weighted median, simple mode, weighted mode, Steiger filtering, MR-PRESSO, and Radial MR analysis, to ensure the robustness of our findings.

RESULTS

The results of our study indicate that there were negative associations between serum vitamin B12 and urate levels, as well as serum folate and the risk of gout. Specifically, we found a negative association between vitamin B12 levels and urate levels, with a β coefficient of -0.324 (95% CI -0.0581 to -0.0066, P = 0.0137) per one standard deviation (SD) increase. Similarly, a negative association was observed between folate levels and gout risk, with an odds ratio of 0.8044 (95% CI 0.6637 to 0.9750, P = 0.0265) per one SD increase. On the other hand, we identified positive associations between serum calcium levels and both urate levels and the risk of gout. Specifically, there was a positive association between serum calcium levels and urate levels (β coefficient: 0.0994, 95% CI 0.0519 to 0.1468, P = 4.11E-05) per one SD increase. Furthermore, a positive association was found between serum calcium levels and the risk of gout, with an odds ratio of 1.1479 (95% CI 1.0460 to 1.2598, P = 0.0036) per one SD increase. These findings were robust in extensive sensitivity analyses. By employing MR-PRESSO and Radial MR to eliminate outliers, the observed associations have been reinforced. No clear associations were found between the other micronutrients and the urate levels, as well as the risk of gout.

CONCLUSION

Our findings provided evidence that there were negative associations between serum vitamin B12 and urate levels, as well as serum folate and the risk of gout, while positive associations existed between the serum calcium levels and urate levels, as well as the risk of gout.

Causal relationship between several autoimmune diseases and renal malignancies: A two-sample mendelian randomization study

OBJECTIVE

Observational studies have shown an association between systemic autoimmune disease (AD) and multiple malignancies. However, due to the difficulty indetermining the temporal nature of the order, their causal relationship remains elusive. Based on pooled data from a large population-wide genome-wide association study (GWAS), this study explores the genetic causality between systemic autoimmune disease and renal malignancy.

METHODS

We took a series of quality control steps from a large-scale genome-wide association study to select single nucleotide polymorphisms (SNPs) associated with systemic autoimmune disease as instrumental variables(IVs) to analyze genetic causality with renal malignancies. Inverse variance weighting (IVW), MR- Egger, weighted median, simple model and weighted model were used for analysis. The results were mainly based on IVW (Random Effects), followed by sensitivity analysis. Inverse-Variance Weighted(IVW) and MR-Egger were used to test for heterogeneity. MR- Egger is also used for pleiotropic testing. A single SNP analysis was used to identify single nucleotide polymorphisms (SNPs) with potential impact. Odds ratio (OR) and 95% confidence interval (CI) were used to evaluate causality, and sensitivity analysis was performed to evaluate pleiotropy and instrumental validity.

RESULTS

Acute and subacute iridocylitis (P = 0.006, OR = 1.077), Ankylosing spondylitis (P = 0.002, OR = 1.051), and spondyloarthritis (P = 0.009, OR = 1.073) were positively associated with an increased risk of renal malignancy. Coxarthrosis (P = 0.008, OR = 0.483), Juvenile rheumatism (P = 0.011, OR = 0.897), and Systemic lupus erythematosus (P = 0.014, OR = 0.869) were negatively associated with an increased risk of renal malignancy. The results of sensitivity analysis were consistent without heterogeneity or pleiotropy.

CONCLUSION

Our study suggests a causal relationship between different systemic autoimmune diseases and renal malignancies. These findings prompt health care providers to take seriously the potential risk of systemic autoimmune disease and provide new insights into the genetics of kidney malignancies.

Lipid Metabolism, Methylation Aberrant, and Osteoporosis: A Multi-omics Study Based on Mendelian Randomization

BACKGROUND

Observational studies have shown a causal association between dyslipidemia and osteoporosis, but the genetic causation and complete mechanism of which are uncertain. The disadvantage of previous observational studies is that they are susceptible to confounding factors and bias, that makes it difficult to infer a causal link between those two diseases. Abnormal epigenetic modifications, represented by DNA methylation, are important causes of many diseases. However, there are no studies showing a bridging role for methylation modifications in blood lipid metabolism and osteoporosis.

METHODS

SNPs for lipid profile (Blood VLDL cholesterol (VLDL-C), blood LDL cholesterol (LDL-C), blood HDL cholesterol (HDL-C), blood triglycerides (TG), diagnosed pure hypercholesterolaemia, blood apolipoprotein B (Apo B), blood apolipoprotein A1(Apo A1)), and bone mineral density (BMD) in different body parts (Heel BMD, lumbar BMD, whole-body BMD, femoral neck BMD) were obtained from large meta-analyses of genome-wide association studies as instrumental variables for two-sample Mendelian randomization. Assessment of the genetic effects of lipid profile-associated methylation sites and bone mineral density was carried out using the summary-data-based Mendelian randomization (SMR) method.

RESULTS

Two-sample Mendelian randomization showed that there was a negative causal association between hypercholesterolaemia and heel BMD (p = 0.0103, OR = 0.4590), and total body BMD (p = 0.0002, OR = 0.2826). LDL-C had a negative causal association with heel BMD (p = 8.68E-05, OR = 0.9586). VLDL-C had a negative causal association with heel BMD (p = 0.035, OR = 0.9484), lumbar BMD (p = 0.0316, OR = 0.9356), and total body BMD (p = 0.0035, OR = 0.9484). HDL-C had a negative causal association with heel BMD (p = 1.25E-05, OR = 0.9548), lumbar BMD (p = 0.0129, OR = 0.9358), and total body BMD (p = 0.0399, OR = 0.9644). Apo B had a negative causal association with heel BMD (p = 0.0001, OR = 0.9647). Apo A1 had a negative causal association with heel BMD (p = 0.0132, OR = 0.9746) and lumbar BMD (p = 0.0058, OR = 0.9261). The p-values of all positive results corrected by the FDR method remained significant and sensitivity analysis showed that there was no horizontal pleiotropy in the results despite the heterogeneity in some results. SMR identified 3 methylation sites associated with lipid profiles in the presence of genetic effects on BMD: cg15707428(GREB1), cg16000331(SREBF2), cg14364472(NOTCH1).

CONCLUSION

Our study provides insights into the potential causal links and co-pathogenesis between dyslipidemia and osteoporosis. The genetic effects of dyslipidaemia on osteoporosis may be related to certain aberrant methylation genetic modifications.

Causal relationship between breakfast skipping and bone mineral density: a two-sample Mendelian randomized study

Objective

To explore the causal association between breakfast skipping and bone mineral density (BMD) through two-sample Mendelian randomisation (MR) analysis.

Methods

A two-sample MR approach was adopted to explore the causal relationship of breakfast skipping with BMDs (across three skeletal sites and five age groups). Publicly available genome-wide association study summary data were used for MR analysis. We used five methods to estimate the causal associations between breakfast skipping and BMDs: inverse-variance weighting (IVW), MR-Egger, weighted median, simple mode, and weighted mode. IVW was used for the main analysis and the remaining four methods were used as supplementary analyses. The heterogeneity of the MR results was determined using IVW and MR-Egger methods. The pleiotropy of the MR results was determined using MR-Egger intercept. Furthermore, a leave-one-out test was performed to determine whether the MR results were affected by a single nucleotide polymorphism.

Results

With the IVW method, we did not find any causal relationship between breakfast skipping and forearm, femoral neck, and lumbar spine BMD. Subsequently, when we included BMD data stratified by five different age groups in the analysis, the results showed that there was no apparent causal effect between breakfast skipping and age-stratified BMD. This finding was supported by all four supplementary methods (P > 0.05 for all methods). No heterogeneity or horizontal pleiotropy was detected in any of the analyses (P > 0.05). The leave-one-out tests conducted in the analyses did not identify any single nucleotide polymorphism that could have influenced the MR results, indicating the reliability of our findings.

Conclusion

No causal effect was found between breakfast skipping and BMD (across three skeletal sites and five age groups).

Appraising causal risk and protective factors for rheumatoid arthritis

Aims

Mendelian randomization (MR) is considered to overcome the bias of observational studies, but there is no current meta-analysis of MR studies on rheumatoid arthritis (RA). The purpose of this study was to summarize the relationship between potential pathogenic factors and RA risk based on existing MR studies.

Methods

PubMed, Web of Science, and Embase were searched for MR studies on influencing factors in relation to RA up to October 2022. Meta-analyses of MR studies assessing correlations between various potential pathogenic factors and RA were conducted. Random-effect and fixed-effect models were used to synthesize the odds ratios of various pathogenic factors and RA. The quality of the study was assessed using the Strengthening the Reporting of Observational Studies in Epidemiology using Mendelian Randomization (STROBE-MR) guidelines.

Results

A total of 517 potentially relevant articles were screened, 35 studies were included in the systematic review, and 19 studies were eligible to be included in the meta-analysis. Pooled estimates of 19 included studies (causality between 15 different risk factors and RA) revealed that obesity, smoking, coffee intake, lower education attainment, and Graves' disease (GD) were related to the increased risk of RA. In contrast, the causality contribution from serum mineral levels (calcium, iron, copper, zinc, magnesium, selenium), alcohol intake, and chronic periodontitis to RA is not significant.

Conclusion

Obesity, smoking, education attainment, and GD have real causal effects on the occurrence and development of RA. These results may provide insights into the genetic susceptibility and potential biological pathways of RA.

Using Mendelian Randomization to Study the Role of Iron in Health and Disease

Iron has been shown to play a dual role in health and disease, with either a protective or harmful effect. Some of the contradictory findings from observational studies may be due to reverse causation, residual confounding, or small sample size. One approach that may overcome these limitations without the high cost of randomized control trials is the use of Mendelian randomization to examine the long-term role of iron in a variety of health outcomes. As there is emerging evidence employing Mendelian randomization as a method of assessing the role of micronutrients in health and disease, this narrative review will highlight recent Mendelian randomization findings examining the role of iron in cardiometabolic disorders, inflammation, neurological disorders, different cancers, and a number of other health-related outcomes.

Association of gout with brain reserve and vulnerability to neurodegenerative disease

Studies of neurodegenerative disease risk in gout are contradictory. Relationships with neuroimaging markers of brain structure, which may offer insights, are uncertain. Here we investigated associations between gout, brain structure, and neurodegenerative disease incidence. Gout patients had smaller global and regional brain volumes and markers of higher brain iron, using both observational and genetic approaches. Participants with gout also had higher incidence of all-cause dementia, Parkinson's disease, and probable essential tremor. Risks were strongly time dependent, whereby associations with incident dementia were highest in the first 3 years after gout diagnosis. These findings suggest gout is causally related to several measures of brain structure. Lower brain reserve amongst gout patients may explain their higher vulnerability to multiple neurodegenerative diseases. Motor and cognitive impairments may affect gout patients, particularly in early years after diagnosis.

No evidence of a genetic causal relationship between ankylosing spondylitis and iron homeostasis: A two-sample Mendelian randomization study

Background

Ankylosing spondylitis (AS) is an immune-mediated chronic inflammatory disease that leads to bone hyperplasia and spinal ankylosis. Iron homeostasis plays a very important role in the inflammatory response and is closely related to the pathogenesis of AS. This study aimed to use large-scale genome-wide association study (GWAS) summary data to study the genetic causal relationship between AS and iron homeostasis using Mendelian randomization (MR).

Methods

Genome-wide association study summary data of AS and iron homeostasis-related indicators were obtained from the FinnGen consortium and the DeCODE genetics database, respectively. We used four iron homeostasis-related indicators: ferritin, serum iron, total iron binding capacity (TIBC), and transferrin saturation (TSAT) for two-sample MR analyses to test for genetic causal association with AS using the "TwoSampleMR" package of the R software (version 4.1.2). The random-effects inverse variance weighted (IVW) method was the main analysis method used for MR. We examined the MR analysis results for heterogeneity, horizontal pleiotropy, and possible outliers. In addition, we confirmed the robustness of the MR analysis by testing whether the results were affected by a single SNP and whether they followed a normal distribution.

Results

The random-effects IVW results showed that ferritin [p = 0.225, OR 95% confidence interval (CI) = 0.836 (0.627-1.116)], serum iron [p = 0.714, OR 95% CI = 0.948 (0.714-1.260)], TIBC [p = 0.380, OR 95% CI = 0.917 (0.755-1.113)], and TSAT [p = 0.674, OR 95% CI = 0.942 (0.713-1.244)] have no genetic causal relationship with AS. We detected no heterogeneity，horizontal pleiotropy and possible outliers in our MR analysis (p > 0.05). In addition, our MR analysis results were not affected by a single SNP, and were normally distributed.

Conclusion

Our study did not detect a genetic causal relationship between AS and iron homeostasis. Nonetheless, this does not rule out a relationship between the two at other mechanistic levels.

Genetic Aspects of Micronutrients Important for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), Crohn’s disease (CD) and ulcerative colitis (UC) are complex diseases whose etiology is associated with genetic and environmental risk factors, among which are diet and gut microbiota. To date, IBD is an incurable disease and the main goal of its treatment is to reduce symptoms, prevent complications, and improve nutritional status and the quality of life. Patients with IBD usually suffer from nutritional deficiency with imbalances of specific micronutrient levels that contribute to the further deterioration of the disease. Therefore, along with medications usually used for IBD treatment, therapeutic strategies also include the supplementation of micronutrients such as vitamin D, folic acid, iron, and zinc. Micronutrient supplementation tailored according to individual needs could help patients to maintain overall health, avoid the triggering of symptoms, and support remission. The identification of individuals’ genotypes associated with the absorption, transport and metabolism of micronutrients can modify future clinical practice in IBD and enable individualized treatment. This review discusses the personalized approach with respect to genetics related to micronutrients commonly used in inflammatory bowel disease treatment.

Genetic Causal Association between Iron Status and Osteoarthritis: A Two-Sample Mendelian Randomization

Objective: Observational studies have shown the association between iron status and osteoarthritis (OA). However, due to difficulties of determining sequential temporality, their causal association is still elusive. Based on the summary data of genome-wide association studies (GWASs) of a large-scale population, this study explored the genetic causal association between iron status and OA. Methods: First, we took a series of quality control steps to select eligible instrumental SNPs which were strongly associated with exposure. The genetic causal association between iron status and OA was analyzed using the two-sample Mendelian randomization (MR). Inverse-variance weighted (IVW), MR-Egger, weighted median, simple mode, and weighted mode methods were used for analysis. The results were mainly based on IVW (random effects), followed by sensitivity analysis. IVW and MR-Egger were used for heterogeneity testing. MR-Egger was also used for pleiotropy testing. Leave-one-SNP-out analysis was used to identify single nucleotide polymorphisms (SNPs) with potential impact. Maximum likelihood, penalized weighted median, and IVW (fixed effects) were performed to further validate the reliability of results. Results: IVW results showed that transferrin saturation had a positive causal association with knee osteoarthritis (KOA), hip osteoarthritis (HOA) and KOA or HOA (p < 0.05, OR > 1), and there was a negative causal association between transferrin and HOA and KOA or HOA (p < 0.05, OR < 1). The results of heterogeneity test showed that our IVW analysis results were basically free of heterogeneity (p > 0.05). The results of the pleiotropy test showed that there was no pleiotropy in our IVW analysis (p > 0.05). The analysis results of maximum likelihood, penalized weighted median and IVW (fixed effects) were consistent with our IVW results. No genetic causal association was found between serum iron and ferritin and OA. Conclusions: This study provides evidence of the causal association between iron status and OA, which provides novel insights to the genetic research of OA.

MiR-129-5p Inactivates NF-κB Pathway to Block Rheumatoid Arthritis Development via Targeting BRD4

Methods

The abundance of miR-129-5p was detected in the samples including normal tissues and RA tissues and cell lines including human fibroblast-like synoviocytes (hFLSs) and human rheumatoid arthritis fibroblast-like synoviocytes (RA-FLSs). The CCK-8 assay, flow cytometry, Transwell, and ELISA were used to observe the effects of miR-129-5p on the phenotype of RA-FLSs. Moreover, the potential targets of miR-129-5p were identified with TargetScan and dual-luciferase reporter gene assay. Besides, the abundances of the proteins were analyzed with western blot.

Results

Decreased miR-129-5p was observed in RA tissues and cells. Increased miR-129-5p obviously blocked the proliferation, inflammatory stress, and migration and remarkably promoted cellular apoptosis. Moreover, BRD4 was confirmed as targets of miR-129-5p, and BRD4 upregulation could partly rescue the inhibition of miR-129-5p on aggressive behaviors of RA-FLSs. Besides, the finding of this study also proved that upregulated miR-129-5p could impede the NF-κB pathway via targeting BRD4.

Conclusion

This study suggests that miR-129-5p suppresses the activation of NF-κB pathway to block the progression of RA via targeting BRD4.

No genetic causal association between iron status and osteoporosis: A two-sample Mendelian randomization

OBJECTIVE

To explore the genetic causal association between osteoporosis (OP) and iron status through Mendelian randomization (MR).

METHODS

Publicly available genome-wide association study (GWAS) summary data were used for MR analysis with four iron status-related indicators (ferritin, iron, total iron binding capacity, and transferrin saturation) as exposures and three different types of OP (OP, OP with pathological fracture, and postmenopausal OP with pathological fracture) as outcomes. The inverse-variance weighted (IVW) method was used to analyze the genetic causal association between the four indicators of iron status and OP. The heterogeneity of MR results was determined using IVW and MR-Egger methods. The pleiotropy of MR results was determined using MR-Egger regression. A leave-one-SNP-out test was performed to determine whether the MR results were affected by a single nucleotide polymorphism (SNP). The weighted median method was conducted to further validate our results.

RESULTS

Based on IVW, MR-Egger and weighted median models, we found no causal association between iron status (ferritin, iron, total iron binding capacity, or transferrin saturation) and OP (P_beta > 0.05 in all models). IVW and MR-Egger analysis of OP with pathological fracture and iron status indicators showed no potential genetic causal association (P_beta> 0.05 in the two analyses). The results of the weighted median were consistent with those of IVW (P_beta> 0.05 in all analyses). There was no potential genetic causal association between iron status and postmenopausal OP with pathological fracture based on serum iron (P_beta>0.05 in all models). No heterogeneity or horizontal pleiotropy was found in any of the analyses. None of the leave-one-out tests in the analyses found any SNP that could affect the results of MR.

CONCLUSION

Our results demonstrate that there is no genetic causal association between OP and iron status, but the effects of other factors were not excluded.

Credible Mendelian Randomization Studies in the Presence of Selection Bias Using Control Exposures

Selection bias is increasingly acknowledged as a limitation of Mendelian randomization (MR). However, few methods exist to assess this issue. We focus on two plausible causal structures relevant to MR studies and illustrate the data-generating process underlying selection bias via simulation studies. We conceptualize the use of control exposures to validate MR estimates derived from selected samples by detecting potential selection bias and reproducing the exposure-outcome association of primary interest based on subject matter knowledge. We discuss the criteria for choosing the control exposures. We apply the proposal in an MR study investigating the potential effect of higher transferrin with stroke (including ischemic and cardioembolic stroke) using transferrin saturation and iron status as control exposures. Theoretically, selection bias affects associations of genetic instruments with the outcome in selected samples, violating the exclusion-restriction assumption and distorting MR estimates. Our applied example showing inconsistent effects of genetically predicted higher transferrin and higher transferrin saturation on stroke suggests the potential selection bias. Furthermore, the expected associations of genetically predicted higher iron status on stroke and longevity indicate no systematic selection bias. The routine use of control exposures in MR studies provides a valuable tool to validate estimated causal effects. Like the applied example, an antagonist, decoy, or exposure with similar biological activity as the exposure of primary interest, which has the same potential selection bias sources as the exposure-outcome association, is suggested as the control exposure. An additional or a validated control exposure with a well-established association with the outcome is also recommended to explore possible systematic selection bias.

Causal risk and protective factors in rheumatoid arthritis: A genetic update

The characterization of risk and protective factors in complex diseases such as rheumatoid arthritis (RA) has evolved from epidemiological studies, which test association, to the use of Mendelian randomization approaches, which test direct relationships. Indeed, direct associations with the mucosal origin of RA are retrieved with periodontal disease (Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans predominantly), interstitial lung involvement, tobacco smoking and air pollutants. Next, factors directly associated with an acquired immune response include genetic factors (HLA DRB1, PTPN22), capacity to produce anti-modified protein antibodies (AMPA), and relatives with a history of autoimmune diseases. Finally, factors can be also classified according to their direct capacity to interfere with the IL-6/CRP/sIL-IL6R proinflammatory pathway as risk factor (body fat, cardiometabolic factors, type 2 diabetes, depressive syndrome) or either as protective factors by controlling of sIL-6R levels (higher education level, and intelligence). Although some co-founders have been characterized (e.g. vitamin D, physical activity, cancer) the direct association with sex-discrepancy, pregnancy, and infections among other factors remains to be better explored.

Genetically Predicted Serum Iron Status Is Associated with Altered Risk of Systemic Lupus Erythematosus among European Populations

BACKGROUND

Observational epidemiological studies have reported an inconsistent relation between iron status and risk of systemic lupus erythematosus (SLE). Moreover, it remains uncertain whether the observed association is causal or due to confounding or reverse causality.

OBJECTIVES

We aimed to investigate the association between serum iron status and risk of SLE using a 2-sample Mendelian randomization (MR) approach.

METHODS

Genetic instruments for iron status including serum iron, log-transformed ferritin, transferrin saturation, and transferrin were identified from a large-scale genome-wide association study (GWAS) performed by the Genetics of Iron Status Consortium among 48,972 individuals of European ancestry (55% female). Three independent single nucleotide polymorphisms (rs1800562, rs1799945, and rs855791) concordantly related with 4 iron status biomarkers were selected as instrumental variables. Summary statistics of SLE were obtained from a publicly available GWAS of 4036 patients with SLE and 6959 controls of European descent. The MR study was conducted using the inverse-variance weighted (IVW) method, supplemented with MR-Egger regression and simple- and weighted-median methods. Leave-one-out analysis was further performed to test the robustness of our findings. ORs with 95% CIs were calculated.

RESULTS

Genetically predicted iron status was associated with altered risk of SLE, with ORs of 0.79 (95% CI: 0.66, 0.94), 0.54 (95% CI: 0.34, 0.85), 0.82 (95% CI: 0.71, 0.94), and 1.36 (95% CI: 1.06, 1.76) per 1-SD increase in iron, log-transformed ferritin, transferrin saturation, and transferrin using the IVW method, respectively. MR-Egger regression did not indicate potential pleiotropic bias. Sensitivity analyses produced similar findings, suggesting the robustness of the association.

CONCLUSIONS

Our study suggested that high iron status may be associated with a reduced risk of SLE among European populations. Further studies are warranted to elucidate the mechanism underlying the protective role of iron against susceptibility to SLE.

Genetics of hyperuricemia and gout: Insights from recent genome-wide association studies and Mendelian randomization studies

Gout is the most common form of inflammatory arthritis in adults. Elevation serum uric acid (SUA) concentration is known to be the key to gout pathogenesis. Since the first genome-wide association study (GWAS) for SUA was performed in 2007, the number of gene loci known to be associated with hyperuricemia and gout has grown rapidly. GWASs and Mendelian randomization studies have also reported numerous novel results regarding the genetics of hyperuricemia and gout since 2018. We concisely review recent advances in scholarship on the effects of genetics on hyperuricemia and gout risk. We also review data from genetic association studies in Taiwan and perform GWASs of SUA levels among Taiwan Biobank participants.

Genetically predicted iron status and life expectancy

Background & aims

Systemic iron status affects multiple health outcomes, however its net effect on life expectancy is not known. We conducted a two-sample Mendelian randomization (MR) study to investigate the association of genetically proxied iron status with life expectancy.

Methods

Using genetic data from 48,972 individuals, we identified three genetic variants as instrumental variables for systemic iron status. We obtained genetic associations of these variants with parental lifespan (n = 1,012,240) and individual survival to the 90th vs. 60th percentile age (11,262 cases and 25,483 controls). We used the inverse-variance weighted method to estimate the effect of a 1-standard deviation (SD) increase in genetically predicted serum iron on each of the life expectancy outcomes.

Results

We found a detrimental effect of genetically proxied higher iron status on life expectancy. A 1-SD increase in genetically predicted serum iron corresponded to 0.70 (95% confidence interval [CI] −1.17, −0.24; P = 3.00 × 10⁻³) fewer years of parental lifespan and had odds ratio 0.81 (95% CI 0.70, 0.93; P = 4.44 × 10⁻³) for survival to the 90th vs. 60th percentile age. We did not find evidence to suggest that these results were biased by pleiotropic effects of the genetic variants.

Conclusions

Higher systemic iron status may reduce life expectancy. The clinical implications of this finding warrant further investigation, particularly in the context of iron supplementation in individuals with normal iron status.

Modifiable environmental exposure and risk of rheumatoid arthritis-current evidence from genetic studies

Rheumatoid arthritis (RA) is a multifactorial chronic autoimmune disease, which involves a complex interplay of environmental triggers and genetic components in its etiology. It has been shown that genetics only explain about half of the liability to develop RA, leaving a large room for non-genetic factors. Indeed, several environmental exposures including smoking, drinking, obesity, and dietary patterns (and more) have been identified to be associated with RA risk, yet the observational nature of conventional epidemiological investigation hampers causal inference, as the validity of results could be plagued by measurement error, confounding, and/or reverse causality. Mendelian randomization (MR) is a novel statistical approach that uses genetic variants as instrumental variables (IV) to make causal inferences from observational data. The current genetic discoveries in the many heritable and modifiable human complex traits have provided an exceptional opportunity to evaluate a putative causal relationship between exposure and outcome in the absence of high-quality experimental or intervention studies, through a MR design. In the current review, we detail the contribution of MR studies hitherto conducted for modifiable environmental exposures with the risk of RA to understand the role of these factors in RA pathogenesis. We start with a brief introduction of each study, follow by a summarization of shortcomings and conclude by highlighting future directions. The application of MR design in the field of rheumatology remains limited. Only a few MR studies have examined the causal roles of vitamin D, cigarette smoking, alcohol consumption, coffee consumption, and levels of education in RA, where, no consistent evidence for a causal relationship has been found. Most studies lacked sensitivity analyses to verify MR model assumptions and to guarantee the validity of results. Almost all studies are likely to bias the strength of association towards a null value, since they used IVs from earlier GWAS(s) of exposures with a small sample size (i.e., few genetic markers). As the magnitudes of GWAS expand rapidly, additional trait-associated loci have been discovered. Incorporating these loci would greatly improve the strength of genetic instruments, as well as both the accuracy and precision of MR estimates. To conclude, there is a need for an update and a huge space for improvement of future MR studies in RA.