Genetically determined circulating levels ofcytokines and the risk of rheumatoid arthritis

Abstract Background: Accumulation of inflammatory leukocytes in articular tissues is the hallmark feature of rheumatoid arthritis (RA). Increasing evidence from observational studies have suggested that several cytokines are relevant in the disease process of RA. However, traditional observational studies are susceptible to bias from confounding and reverse causation; therefore, the potential causal association of individual cytokines with the risk of RA remains elusive. Our study aimed to evaluate whether genetically determined circulating levels of cytokines are associated with the risk of RA by conducting a two-sample Mendelian randomization (MR) study.Methods: We identified single nucleotide polymorphisms (SNPs) associated with circulating levels of cytokines and growth factors from a genome-wide association study (GWAS) including 8,293 participants of European ancestry as instrumental variables (IVs). The association estimates of these IVs with RA were obtained from a GWAS meta-analysis including 14,361 RA cases and 43,923 controls of European ancestry. MR analyses were performed using the random-effects inverse variance-weighted, weighted-median, MR-Egger and MR pleiotropy residual sum and outlier tests. Sensitivity analyses were further performed using restricted IVs excluding potential pleiotropic SNPs.Results: In the primary MR analysis, a total of 270 SNPs associated with circulating levels of 27 cytokines were identified and used as IVs. We found a suggestive inverse association between genetically determined circulating level of macrophage inflammatory protein-1β (MIP-1b) and the risk of RA [odds ratio (OR): 0.97, 95% confidence interval (CI) = 0.92-0.99, P = 0.016]. The association remained statistically significant in alternative MR analyses, and the causal effect estimate from sensitivity analysis using the restricted IVs was similar.Conclusions: Genetically determined elevated circulating level of MIP-1b was associated with a lower risk of RA. Further studies are warranted to determine how this MIP-1b and related pathways contribute to the development of RA.

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Investigating the causal effect of maternal vitamin B12 and folate levels on offspring birthweight

10.1101/2020.01.21.914655 ◽

2020 ◽

Author(s):

Gunn-Helen Moen ◽

Robin N Beaumont ◽

Christine Sommer ◽

Beverley M. Shields ◽

Deborah A Lawlor ◽

...

Keyword(s):

Vitamin B12 ◽

Genetic Variants ◽

Observational Studies ◽

Genome Wide Association Study ◽

Causal Effect ◽

Meta Analysis ◽

Serum Vitamin ◽

Genetic Effects ◽

Sensitivity Analyses ◽

A Genome

AbstractLower maternal serum vitamin B12 (B12) and folate levels have been associated with lower offspring birthweight in observational studies. The aim of this study was to investigate whether this relationship is causal.We performed two-sample Mendelian Randomization (MR) using summary data on associations between genotype-B12 (10 genetic variants) or genotype-folate (4 genetic variants) levels from a genome-wide association study of 45,576 individuals (sample 1) and maternal-specific genetic effects on offspring birthweight from the latest EGG consortium meta-analysis with 297,356 individuals reporting their own birthweight and 210,248 women reporting their offspring’s birthweight (sample 2). To investigate the effect of offspring’s own B12 or folate levels on their own birthweight, we performed two-sample MR using the fetal-specific genetic effects from the latest EGG consortium meta-analysis. We used the inverse variance weighted method, and sensitivity analyses to account for pleiotropy, in addition to sensitivity analyses excluding a potentially pleiotropic variant in the FUT2 gene for B12.We did not find evidence for a causal effect of maternal B12 on offspring birthweight, nor evidence for an effect of offspring B12 on their own birthweight using the fetal-specific genetic effect. The results were consistent across the different methods and in sensitivity analyses excluding the FUT2 variant. We found a positive effect of maternal folate on offspring birthweight (0.146 [0.065, 0.227], which corresponds to an increase in birthweight of 71g per 1SD higher folate). We found some evidence for a small inverse effect of fetal folate on their own birthweight (−0.051 [−0.100, −0.003]).In conclusion, our results are consistent with evidence from randomized controlled trials that increased maternal folate levels increase offspring birthweight. We did not find evidence for a causal effect of B12 on offspring birthweight, suggesting previous observational studies may have been due to confounding.

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The Effect of Circulating Zinc, Selenium, Copper and Vitamin K1 on COVID-19 Outcomes: A Mendelian Randomization Study

Nutrients ◽

10.3390/nu14020233 ◽

2022 ◽

Vol 14 (2) ◽

pp. 233

Author(s):

Maria K. Sobczyk ◽

Tom R. Gaunt

Keyword(s):

Critical Illness ◽

Mendelian Randomization ◽

Causal Effect ◽

Sensitivity Analyses ◽

European Ancestry ◽

P Value ◽

Vitamin K1 ◽

Inverse Variance ◽

A Genome

Background & Aims: Previous results from observational, interventional studies and in vitro experiments suggest that certain micronutrients possess anti-viral and immunomodulatory activities. In particular, it has been hypothesized that zinc, selenium, copper and vitamin K1 have strong potential for prophylaxis and treatment of COVID-19. We aimed to test whether genetically predicted Zn, Se, Cu or vitamin K1 levels have a causal effect on COVID-19 related outcomes, including risk of infection, hospitalization and critical illness. Methods: We employed a two-sample Mendelian Randomization (MR) analysis. Our genetic variants derived from European-ancestry GWAS reflected circulating levels of Zn, Cu, Se in red blood cells as well as Se and vitamin K1 in serum/plasma. For the COVID-19 outcome GWAS, we used infection, hospitalization or critical illness. Our inverse-variance weighted (IVW) MR analysis was complemented by sensitivity analyses including a more liberal selection of variants at a genome-wide sub-significant threshold, MR-Egger and weighted median/mode tests. Results: Circulating micronutrient levels show limited evidence of association with COVID-19 infection, with the odds ratio [OR] ranging from 0.97 (95% CI: 0.87–1.08, p-value = 0.55) for zinc to 1.07 (95% CI: 1.00–1.14, p-value = 0.06)—i.e., no beneficial effect for copper was observed per 1 SD increase in exposure. Similarly minimal evidence was obtained for the hospitalization and critical illness outcomes with OR from 0.98 (95% CI: 0.87–1.09, p-value = 0.66) for vitamin K1 to 1.07 (95% CI: 0.88–1.29, p-value = 0.49) for copper, and from 0.93 (95% CI: 0.72–1.19, p-value = 0.55) for vitamin K1 to 1.21 (95% CI: 0.79–1.86, p-value = 0.39) for zinc, respectively. Conclusions: This study does not provide evidence that supplementation with zinc, selenium, copper or vitamin K1 can prevent SARS-CoV-2 infection, critical illness or hospitalization for COVID-19.

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Depression and Osteoporosis: A Mendelian Randomization Study

Calcified Tissue International ◽

10.1007/s00223-021-00886-5 ◽

2021 ◽

Author(s):

Bin He ◽

Qiong Lyu ◽

Lifeng Yin ◽

Muzi Zhang ◽

Zhengxue Quan ◽

...

Keyword(s):

Observational Studies ◽

Mendelian Randomization ◽

Causal Effect ◽

Association Studies ◽

Meta Analysis ◽

Sensitivity Analyses ◽

European Ancestry ◽

Genome Wide Association Studies ◽

Reverse Causality ◽

Mineral Density

AbstractObservational studies suggest a link between depression and osteoporosis, but these may be subject to confounding and reverse causality. In this two-sample Mendelian randomization analysis, we included the large meta-analysis of genome-wide association studies for depression among 807,553 individuals (246,363 cases and 561,190 controls) of European descent, the large meta-analysis to identify genetic variants associated with femoral neck bone mineral density (FN-BMD), forearm BMD (FA-BMD) and lumbar spine BMD (LS-BMD) among 53,236 individuals of European ancestry, and the GWAS summary data of heel BMD (HE-BMD) and fracture among 426,824 individuals of European ancestry. The results revealed that genetic predisposition towards depression showed no causal effect on FA-BMD (beta-estimate: 0.091, 95% confidence interval [CI] − 0.088 to 0.269, SE:0.091, P value = 0.320), FN-BMD (beta-estimate: 0.066, 95% CI − 0.016 to 0.148, SE:0.042, P value = 0.113), LS-BMD (beta-estimate: 0.074, 95% CI − 0.029 to 0.177, SE:0.052, P value = 0.159), HE-BMD (beta-estimate: 0.009, 95% CI − 0.043 to 0.061, SE:0.027, P value = 0.727), or fracture (beta-estimate: 0.008, 95% CI − 0.071 to 0.087, SE:0.041, P value = 0.844). These results were also confirmed by multiple sensitivity analyses. Contrary to the findings of observational studies, our results do not reveal a causal role of depression in osteoporosis or fracture.

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Vitamin D and COVID-19 susceptibility and severity in the COVID-19 Host Genetics Initiative: A Mendelian randomization study

PLoS Medicine ◽

10.1371/journal.pmed.1003605 ◽

2021 ◽

Vol 18 (6) ◽

pp. e1003605

Author(s):

Guillaume Butler-Laporte ◽

Tomoko Nakanishi ◽

Vincent Mooser ◽

David R. Morrison ◽

Tala Abdullah ◽

...

Keyword(s):

Vitamin D ◽

Mendelian Randomization ◽

Causal Effect ◽

Severe Disease ◽

Sensitivity Analyses ◽

European Ancestry ◽

Logarithmic Scale ◽

Host Genetics ◽

A Genome ◽

Vitamin D Levels

Background Increased vitamin D levels, as reflected by 25-hydroxy vitamin D (25OHD) measurements, have been proposed to protect against COVID-19 based on in vitro, observational, and ecological studies. However, vitamin D levels are associated with many confounding variables, and thus associations described to date may not be causal. Vitamin D Mendelian randomization (MR) studies have provided results that are concordant with large-scale vitamin D randomized trials. Here, we used 2-sample MR to assess evidence supporting a causal effect of circulating 25OHD levels on COVID-19 susceptibility and severity. Methods and findings Genetic variants strongly associated with 25OHD levels in a genome-wide association study (GWAS) of 443,734 participants of European ancestry (including 401,460 from the UK Biobank) were used as instrumental variables. GWASs of COVID-19 susceptibility, hospitalization, and severe disease from the COVID-19 Host Genetics Initiative were used as outcome GWASs. These included up to 14,134 individuals with COVID-19, and up to 1,284,876 without COVID-19, from up to 11 countries. SARS-CoV-2 positivity was determined by laboratory testing or medical chart review. Population controls without COVID-19 were also included in the control groups for all outcomes, including hospitalization and severe disease. Analyses were restricted to individuals of European descent when possible. Using inverse-weighted MR, genetically increased 25OHD levels by 1 standard deviation on the logarithmic scale had no significant association with COVID-19 susceptibility (odds ratio [OR] = 0.95; 95% CI 0.84, 1.08; p = 0.44), hospitalization (OR = 1.09; 95% CI: 0.89, 1.33; p = 0.41), and severe disease (OR = 0.97; 95% CI: 0.77, 1.22; p = 0.77). We used an additional 6 meta-analytic methods, as well as conducting sensitivity analyses after removal of variants at risk of horizontal pleiotropy, and obtained similar results. These results may be limited by weak instrument bias in some analyses. Further, our results do not apply to individuals with vitamin D deficiency. Conclusions In this 2-sample MR study, we did not observe evidence to support an association between 25OHD levels and COVID-19 susceptibility, severity, or hospitalization. Hence, vitamin D supplementation as a means of protecting against worsened COVID-19 outcomes is not supported by genetic evidence. Other therapeutic or preventative avenues should be given higher priority for COVID-19 randomized controlled trials.

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Investigating the causal effect of maternal vitamin B12 and folate levels on offspring birthweight

International Journal of Epidemiology ◽

10.1093/ije/dyaa256 ◽

2020 ◽

Author(s):

Gunn-Helen Moen ◽

Robin N Beaumont ◽

Niels Grarup ◽

Christine Sommer ◽

Beverley M Shields ◽

...

Keyword(s):

Vitamin B12 ◽

Genetic Variants ◽

Observational Studies ◽

Genome Wide Association Study ◽

Causal Effect ◽

Meta Analysis ◽

Serum Vitamin ◽

Maternal Serum ◽

Sensitivity Analyses ◽

A Genome

Abstract Background Lower maternal serum vitamin B12 (B12) and folate levels have been associated with lower offspring birthweight, in observational studies. The aim of this study was to investigate whether this relationship is causal. Methods We performed two-sample Mendelian randomization (MR) using summary data on associations between genotype-B12 (10 genetic variants) or genotype-folate (four genetic variants) levels from: a genome-wide association study of 45 576 individuals (sample 1); and both maternal- and fetal-specific genetic effects on offspring birthweight from the latest Early Growth Genetics consortium meta-analysis with 297 356 individuals reporting their own birthweight and 210 248 women reporting their offspring's birthweight (sample 2). We used the inverse variance weighted method, and sensitivity analyses to account for pleiotropy, in addition to excluding a potentially pleiotropic variant in the FUT2 gene for B12 levels. Results We did not find evidence for a causal effect of maternal or fetal B12 levels on offspring birthweight. The results were consistent across the different methods. We found a positive causal effect of maternal folate levels on offspring birthweight [0.146 (0.065, 0.227), which corresponds to an increase in birthweight of 71 g per 1 standard deviation higher folate]. We found some evidence for a small inverse effect of fetal folate levels on their own birthweight [−0.051 (−0.100, −0.003)]. Conclusions Our results are consistent with evidence from randomized controlled trials that higher maternal folate levels increase offspring birthweight. We did not find evidence for a causal effect of B12 levels on offspring birthweight, suggesting previous observational studies may have been confounded.

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Bias in two-sample Mendelian randomization when using heritable covariable-adjusted summary associations

International Journal of Epidemiology ◽

10.1093/ije/dyaa266 ◽

2021 ◽

Author(s):

Fernando Pires Hartwig ◽

Kate Tilling ◽

George Davey Smith ◽

Deborah A Lawlor ◽

Maria Carolina Borges

Keyword(s):

Waist Circumference ◽

Genetic Variants ◽

Mendelian Randomization ◽

Causal Effect ◽

Association Studies ◽

Real Data ◽

Sensitivity Analyses ◽

Effect Estimate ◽

Genome Wide Association Studies ◽

Residual Confounding

Abstract Background Two-sample Mendelian randomization (MR) allows the use of freely accessible summary association results from genome-wide association studies (GWAS) to estimate causal effects of modifiable exposures on outcomes. Some GWAS adjust for heritable covariables in an attempt to estimate direct effects of genetic variants on the trait of interest. One, both or neither of the exposure GWAS and outcome GWAS may have been adjusted for covariables. Methods We performed a simulation study comprising different scenarios that could motivate covariable adjustment in a GWAS and analysed real data to assess the influence of using covariable-adjusted summary association results in two-sample MR. Results In the absence of residual confounding between exposure and covariable, between exposure and outcome, and between covariable and outcome, using covariable-adjusted summary associations for two-sample MR eliminated bias due to horizontal pleiotropy. However, covariable adjustment led to bias in the presence of residual confounding (especially between the covariable and the outcome), even in the absence of horizontal pleiotropy (when the genetic variants would be valid instruments without covariable adjustment). In an analysis using real data from the Genetic Investigation of ANthropometric Traits (GIANT) consortium and UK Biobank, the causal effect estimate of waist circumference on blood pressure changed direction upon adjustment of waist circumference for body mass index. Conclusions Our findings indicate that using covariable-adjusted summary associations in MR should generally be avoided. When that is not possible, careful consideration of the causal relationships underlying the data (including potentially unmeasured confounders) is required to direct sensitivity analyses and interpret results with appropriate caution.

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No evidence that vitamin D is able to prevent or affect the severity of COVID-19 in individuals with European ancestry: a Mendelian randomisation study of open data

BMJ Nutrition, Prevention & Health ◽

10.1136/bmjnph-2020-000151 ◽

2021 ◽

pp. bmjnph-2020-000151

Author(s):

Hasnat A Amin ◽

Fotios Drenos

Keyword(s):

Vitamin D ◽

Vitamin D Deficiency ◽

Causal Effect ◽

Infection Risk ◽

European Ancestry ◽

Mendelian Randomisation ◽

Upper Respiratory Tract ◽

A Genome ◽

Vitamin D Levels ◽

Tract Infections

BackgroundUpper respiratory tract infections are reportedly more frequent and more severe in individuals with lower vitamin D levels. Based on these findings, it has been suggested that vitamin D can prevent or reduce the severity of COVID-19.MethodsWe used two-sample Mendelian randomisation (MR) to assess the causal effect of vitamin D levels on SARS-CoV-2 infection risk and COVID-19 severity using publicly available data. We also carried out a genome-wide association analysis (GWA) of vitamin D deficiency in the UK Biobank (UKB) and used these results and two-sample MR to assess the causal effect of vitamin D deficiency on SARS-CoV-2 infection risk and COVID-19 severity.ResultsWe found no evidence that vitamin D levels causally affect the risk of SARS-CoV-2 infection (ln(OR)=0.17 (95% CI −0.22 to 0.57, p=0.39)) nor did we find evidence that vitamin D levels causally affect COVID-19 severity (ln(OR)=0.36 (95% CI −0.89 to 1.61, p=0.57)). Based on our GWA analysis, we found that 17 independent variants are associated with vitamin D deficiency in the UKB. Using these variants as instruments for our two-sample MR analyses, we found no evidence that vitamin D deficiency causally affects the risk of SARS-CoV-2 infection (ln(OR)=−0.04 (95% CI −0.1 to 0.03, p=0.25)) nor did we find evidence that vitamin D deficiency causally affects COVID-19 severity (ln(OR)=−0.24 (95% CI −0.55 to 0.08, p=0.14)).ConclusionsIn conclusion, we found no evidence that vitamin D is protective against SARS-CoV-2 infection or COVID-19 severity. Our data support the recent statement by the National Institute for Health and Care Excellence that the use of vitamin D supplementation to mitigate COVID-19 is not supported by the available data.

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Plasma lipid levels and risk of primary open angle glaucoma: a genetic study using Mendelian randomization

BMC Ophthalmology ◽

10.1186/s12886-020-01661-0 ◽

2020 ◽

Vol 20 (1) ◽

Author(s):

Mengqiao Xu ◽

Shengguo Li ◽

Jundong Zhu ◽

Dawei Luo ◽

Weitao Song ◽

...

Keyword(s):

Primary Open Angle Glaucoma ◽

Mendelian Randomization ◽

Open Angle Glaucoma ◽

Plasma Lipid ◽

Sensitivity Analyses ◽

European Ancestry ◽

Open Angle ◽

Causal Association ◽

Lipid Levels ◽

A Genome

Abstract Background The causal effects of plasma lipid concentrations and the risk of primary open angle glaucoma (POAG) are still unclear. Thus, the purpose of this study was to identify, applying a two-sample Mendelian randomization (MR) analysis, whether plasma lipid concentrations are causally associated with the risk of POAG. Methods Two-sample MR analysis of data from a genome-wide association study (GWAS) was performed to investigate the causal role of plasma lipid levels and POAG. A total of 185 independent single-nucleotide polymorphisms (SNPs) associated with plasma lipid levels were selected as instrumental variables (IVs). The SNPs were obtained from a meta-analysis of GWAS based on 188,577 European-ancestry individuals for MR analyses. Association with POAG for the SNPs was obtained from a GWAS conducted among the United Kingdom (UK) Biobank study participants with a total of 463,010 European-ancestry individuals. Four MR methods (inverse variance weighted [IVW], weighted mode, weighted median, and MR-Egger regression) were applied to obtain the overall causal estimate for multiple, instrumental SNPs. Results Using the IVW analysis method, no evidence was found to support a causal association between plasma LDL-C level and POAG risk (β = − 0.00026; 95% CI = -0.00062, 0.00011; P = 0.165) with no significant heterogeneity among SNPs. The overall causal estimate between plasma LDL-C level and POAG was consistent using the other three MR methods. Using the four MR methods, no evidence of an association between plasma HDL-C (β = 0.00023; 95% CI = -0.00015, 0.00061; P = 0.238; IVW method) or TG levels (β = − 0.00028; 95% CI = -0.00071, 0.00015; P = 0.206; IVW method) and POAG risk was found. Sensitivity analyses did not reveal any sign of directional pleiotropy. Conclusions The present study did not find any evidence for a causal association between plasma lipid levels and POAG risk. Further research is needed to elucidate the potential biological mechanisms to provide a reasonable interpretation for these results.

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P6231Iron status and risk of cardio-metabolic diseases in European adults: a Mendelian randomization study

European Heart Journal ◽

10.1093/eurheartj/ehz746.0833 ◽

2019 ◽

Vol 40 (Supplement_1) ◽

Author(s):

W Gan ◽

D Bennett ◽

A Mahajan ◽

H Du ◽

Z Chen ◽

...

Keyword(s):

Serum Iron ◽

Metabolic Diseases ◽

Mendelian Randomization ◽

Iron Status ◽

Transferrin Saturation ◽

Sensitivity Analyses ◽

European Ancestry ◽

Research Centre ◽

Inverse Association ◽

Total N

Abstract Background Observational studies have reported conflicting results about the associations of iron status with risk of cardio-metabolic diseases but such studies are constrained by confounding and reverse causality. Purpose To assess the causal relevance of iron status biomarkers (transferrin, serum iron, and ferritin) for risk of coronary artery diseases (CAD), ischaemic stroke (IS), and type 2 diabetes (T2D), using Mendelian randomization (MR). Methods Effect size estimates for genetic variants associated with iron status biomarkers were obtained from the Genetics of Iron Status consortium (transferrin saturation, serum iron, and ferritin: n=48,972). The corresponding effects of these variants on the risk of CAD, IS and T2D were obtained from a meta-analysis of unrelated participants of European ancestry in the UK Biobank (UKB), together with previously recruited participants in CARDIOGRAMplusC4D (total n=90,377 CAD cases), MEGASTROKE (total n=43,381 IS cases) and DIAGRAM (total n=74,124 T2D cases), respectively. The main analysis used a two-sample inverse-variance weighted MR, while the sensitivity analyses used weighted-median, weighted-mode, MR-PRESSO, and MR-Egger approaches. Results MR analysis demonstrated significant inverse association of each of the three genetically-instrumented iron status biomarker with risk of CAD (transferrin saturation OR=0.96 [95% CI: 0.92–0.99], p=0.02; serum iron OR=0.93 [0.89–0.97], p=0.001; and ferritin OR=0.86 (0.79–0.94), p=0.001, per 1 SD higher level). In contrast, these iron status biomarkers showed positive associations with risk of T2D (transferrin saturation OR=1.06 [1.01–1.11], p=0.01; serum iron OR=1.06 [0.99–1.13], p=0.07; and ferritin OR=1.12 [0.99–1.26], p=0.06, per 1 SD higher level). There was positive, but non-significant, association of IS with each of the iron status biomarker analysed. Sensitivity analyses using several different MR approaches yielded concordant results. Conclusions Among European adults, iron status appeared to have causal associations, but in opposite directions, with the risk of CHD and T2D. Our findings highlight the need for caution about strategies for advocating iron supplementation in individuals with normal haemoglobin levels for prevention of CAD. Acknowledgement/Funding British Heart Found, Medical Research Council, Wellcome Trust, NIHR Biomedical Research Centre, Oxford

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Iron Status May Not Affect Amyotrophic Lateral Sclerosis: A Mendelian Randomization Study

Frontiers in Genetics ◽

10.3389/fgene.2021.617245 ◽

2021 ◽

Vol 12 ◽

Author(s):

Jiahao Cai ◽

Xiong Chen ◽

Hongxuan Wang ◽

Zixin Wei ◽

Mei Li ◽

...

Keyword(s):

Amyotrophic Lateral Sclerosis ◽

Genome Wide Association Study ◽

Mendelian Randomization ◽

Causal Effect ◽

Iron Status ◽

Transferrin Saturation ◽

Outcome Data ◽

Sensitivity Analyses ◽

A Genome ◽

Lateral Sclerosis

BackgroundObservational studies have shown an association of increased iron status with a higher risk of amyotrophic lateral sclerosis (ALS). Iron status might be a novel target for ALS prevention if a causal relationship exists. We aimed to reveal the causality between iron status and ALS incidence using a large two-sample Mendelian randomization (MR).MethodsSingle nucleotide polymorphisms (SNPs) for iron status were identified from a genome-wide association study (GWAS) on 48,972 individuals. The outcome data came from the largest ALS GWAS to date (20,806 cases; 59,804 controls). We conducted conservative analyses (using SNPs with concordant change of biomarkers of iron status) and liberal analyses (using SNPs associated with at least one of the biomarkers of iron status), with inverse variance weighted (IVW) method as the main analysis. We then performed sensitivity analyses including weighted median, MR-Egger and MR-pleiotropy residual sum and outlier, as well as leave-one-out analysis to detect pleiotropy.ResultsIn the conservative analyses, we found no evidence of association between four biomarkers of iron status and ALS using IVW method with odds ratio (OR) 1.00 [95% confidence interval (CI): 0.90–1.11] per standard deviation (SD) increase in iron, 0.96 (95% CI: 0.77–1.21) in ferritin, 0.99 (95% CI: 0.92–1.07) in transferrin saturation, and 1.04 (95% CI: 0.93–1.16) in transferrin. Findings from liberal analyses were similar, and sensitivity analyses suggested no pleiotropy detected (all p > 0.05).ConclusionOur findings suggest no causal effect between iron status and risk of ALS. Efforts to change the iron status to decrease ALS incidence might be impractical.

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