Mendelian randomization analysis reveals a causal relationship between preterm birth and myopia risk.

<p>Preterm birth is defined as delivery prior to 37 weeks’ completed gestation. It affects an average of 11% of pregnancies worldwide and is the leading cause of death in children under age 5. Many studies have identified associations between pregnancy lipid levels and increased risk for preterm birth. This thesis investigates the role of genetic variability associated with lipids and its relationship with preterm birth, and the relationship between pre-pregnancy dyslipidemia and risk for preterm birth.</p> <p>Genetic variability in the form of single-nucleotide polymorphisms, previously identified by genome-wide association studies for association with lipid levels, was analyzed for association with risk for preterm birth. The study population included 992 women in California with banked 2nd trimester serum samples. Serum lipid levels and DNA were used. Genetic risk scores were constructed for each subject using published SNPs associated with lipid levels as an indicator of genetic burden. These genetic risk scores were then analyzed for association with risk for preterm birth. The GRS were not associated with the overall risk for preterm birth. However, a higher HDL-C GRS was associated with increased risk for spontaneous preterm birth. Higher triglyceride and total cholesterol GRS were associated with decreased risk for spontaneous preterm birth.</p> <p>The relationship between pre-pregnancy dyslipidemia and risk for preterm birth was assessed in a cohort of 2,962,434 women giving birth in the state of California from 2007-2012. Dyslipidemia, as defined by medical diagnostic codes, was associated with a 1.5-fold increase in risk for preterm birth. This association was consistent across race/ethnicity, body mass index, type of dyslipidemia, and type of preterm birth.</p> <p>This thesis identified counter-intuitive associations between lipid GRS and spontaneous preterm birth, while also identifying a strong relationship between pre-pregnancy dyslipidemia and all types of preterm birth including spontaneous. Together, these findings suggest that the previously reported associations between lipids and preterm birth may be reflecting unidentified dyslipidemias. One possible interpretation of the counter-intuitive genetic findings is that while extreme dyslipidemia predisposes to preterm birth a genetic predisposition to low total cholesterol also confers increased risk for spontaneous preterm birth. An alternative explanation is that these results are simply an artefact of the data and additional genetic loci and lifestyle factors confer stronger effects on risk for spontaneous PTB than the effects of the genetic loci included in this thesis.</p>

BackgroundAs the number of COVID-19 deaths continues to rise worldwide, the identification of risk factors for the disease is an urgent issue, and it remains controversial whether atherogenic lipid-related traits including serum apolipoprotein B, low-density lipoprotein (LDL)-cholesterol, and triglyceride levels, are risk factors. The aim of this study was to estimate causal effects of lipid-related traits on COVID-19 risk in the European population using a two-sample Mendelian randomization (MR) approach.MethodsWe used summary statistics from a genome-wide association study (GWAS) that included 441,016 participants from the UK Biobank as the exposure dataset of lipid-related traits and from COVID-19 Host Genetics Initiative GWAS meta-analyses of European ancestry as the outcome dataset for COVID-19 susceptibility (32,494 cases and 1,316,207 controls), hospitalization (8316 cases and 1,549,095 controls), and severity (4792 cases and 1,054,664 controls). We performed two-sample MR analyses using the inverse variance weighted (IVW) method. As sensitivity analyses, the MR-Egger regression, weighted median, and weighted mode methods were conducted as were leave-one-out sensitivity analysis, the MR-PRESSO global test, PhenoScanner searches, and IVW multivariable MR analyses. A P value below 0.0055 with Bonferroni correction was considered statistically significant.ResultsThis MR study suggested that serum apolipoprotein B or LDL-cholesterol levels were not significantly associated with COVID-19 risk. On the other hand, we inferred that higher serum triglyceride levels were suggestively associated with higher risks of COVID-19 susceptibility (odds ratio [OR] per standard deviation increase in lifelong triglyceride levels, 1.065; 95% confidence interval [CI], 1.001–1.13; P = 0.045) and hospitalization (OR, 1.174; 95% CI, 1.04–1.33; P = 0.012), and were significantly associated with COVID-19 severity (OR, 1.274; 95% CI, 1.08–1.50; P = 0.004). Sensitivity and bidirectional MR analyses suggested that horizontal pleiotropy and reverse causation were unlikely.ConclusionsOur MR study indicates a causal effect of higher serum triglyceride levels on a greater risk of COVID-19 severity in the European population using the latest and largest GWAS datasets to date. However, as the underlying mechanisms remain unclear and our study might be still biased due to possible horizontal pleiotropy, further studies are warranted to validate our findings and investigate underlying mechanisms.

Preterm birth poses significant risks to neonatal health. Although immune dysregulation has been implicated in its etiology, the causal roles of specific immune cell phenotypes and the potential mediating effects of metabolites remain unclear. This study applied Mendelian randomization (MR) to investigate causal relationships between immune cell phenotypes and preterm birth, and to assess whether plasma metabolites mediate these associations. Two-sample and mediation MR analyses were performed using genetic variants from genome-wide association studies (GWAS) of immune cells and plasma metabolites. Causal estimates were primarily derived using inverse variance weighting (IVW), with sensitivity analyses conducted via MR-Egger, MR-PRESSO, and leave-one-out validation. A total of 28 immune cell phenotypes and 47 metabolites were robustly associated with preterm birth (P < 0.05). Reverse MR analysis revealed no evidence of reverse causality for the identified immune phenotypes. Among these, CD28- CD8br AC exhibited the strongest association with increased preterm birth risk. Mediation analysis demonstrated that the effect of CD28- CD8br AC on preterm birth (total effect: 0.148; IVW OR [95% CI]: 1.160 [1.056-1.274], P = 0.002) was partially mediated by isoleucine levels (mediation proportion: 6.79%; P = 0.027) and the acetylcarnitine-to-propionylcarnitine (C2/C3) ratio (mediation proportion: 7.35%; P = 0.029). Sensitivity analyses confirmed the robustness of these findings. This study establishes causal links between immune cell phenotypes, metabolites, and genetic susceptibility to preterm birth. Specifically, CD28- CD8br AC may elevate preterm birth risk through modulation of isoleucine and the C2/C3 ratio, providing novel insights into disease mechanisms and potential therapeutic targets.

BackgroundThe prevalence of youth anxiety and depression has increased globally, with limited causal explanations. Long-term physical health conditions (LTCs) affect 20–40% of youth, with rates also rising. LTCs are associated with higher rates of youth depression and anxiety; however, it is uncertain whether observed associations are causal or explained by unmeasured confounding or reverse causation.MethodsUsing data from the Norwegian Mother, Father, and Child Cohort Study (MoBa) and Norwegian National Patient Registry, we investigated phenotypic associations between childhood LTCs, and depression and anxiety diagnoses in youth (<19 years), defined using ICD-10 diagnoses and self-rated measures. We then conducted two-sample Mendelian Randomization (MR) analyses using SNPs associated with childhood LTCs from existing genome-wide association studies (GWAS) as instrumental variables. Outcomes were: (i) diagnoses of major depressive disorder (MDD) and anxiety disorders or elevated symptoms in MoBa, and (ii) youth-onset MDD using summary statistics from a GWAS in iPSYCH2015 cohort.ResultsHaving any childhood LTC phenotype was associated with elevated youth MDD (OR = 1.48 [95% CIs 1.19, 1.85], p = 4.2×10−4) and anxiety disorder risk (OR = 1.44 [1.20, 1.73], p = 7.9×10−5). Observational and MR analyses in MoBa were consistent with a causal relationship between migraine and depression (IVW OR = 1.38 [1.19, 1.60], pFDR = 1.8x10−4). MR analyses using iPSYCH2015 did not support a causal link between LTC genetic liabilities and youth-onset depression or in the reverse direction.ConclusionsChildhood LTCs are associated with depression and anxiety in youth, however, little evidence of causation between LTCs genetic liability and youth depression/anxiety was identified from MR analyses, except for migraine.

The correlation between obesity and primary open-angle glaucoma (POAG) has not yet been fully established. The aim of this study was to investigate the causal relationship between obesity and POAG by a two-sample Mendelian randomization (MR) study. In this study, body mass index (BMI), an index to evaluate general obesity, and waist and hip circumference, indices to evaluate abdominal obesity, were selected as exposures in MR analysis. Single-nucleotide polymorphisms (SNPs) were chosen as instrumental variables (IVs). Summary data from genome-wide association studies (GWASs) based on a European ancestry by Locke et al., with regard to BMI, and Shungin et al., with regard to waist and hip circumference, were used. Genetic predictors of POAG were obtained from public GWAS summary data. To assess the causal effect of obesity on POAG, the inverse variance-weighted (IVW) method was used as the primary method, and other methods, such as MR–Egger, weighted median, simple mode, and weighted mode, were also used as complementary analyses. Finally, we performed Cochran’s Q statistic to assess heterogeneity, and sensitivity analysis was performed to evaluate the reliability and stability of the MR results. MR analysis showed that BMI has a positive effect on the risk of POAG, with 1 standard deviation (SD) increase in BMI; the risk of POAG increases by approximately 90.9% [OR = 1.909; 95% CI= (1.225, 2.975); p = 0.0042)] (analyzed by IVW); there were no heterogeneity and pleiotropy in the result; and waist circumference also had a positive effect on the risk of POAG [OR = 2.319; 95% CI= (1.071, 5.018); p = 0.033)] analyzed by weighted median. As hip circumference increases, with 1 SD increase in hip circumference, the risk of POAG increases by approximately 119% [OR = 2.199; 95% CI= (1.306, 3.703); p = 0.00305)] estimated by IVW, there were not heterogeneity and pleiotropy as for the result. Our study for the first time confirms that obesity might increase the risk of POAG using two-sample MR analysis. These results might provide guidance on the prevention and treatment of POAG.

The causal association between vitamin E status and osteoarthritis (OA) remains controversial in previous epidemiological studies. We employed a Mendelian randomization (MR) analysis to explore the causal relationship between circulating alpha-tocopherol levels (main forms of vitamin E in our body) and OA. The instrumental variables (IVs) of circulating alpha-tocopherol levels were obtained from a Genome-wide association study (GWAS) dataset of 7781 individuals of European descent. The outcome of OA was derived from the UK biobank. Two-sample MR analysis was used to estimate the causal relationship between circulating alpha-tocopherol levels and OA. The inverse-variance weighted (IVW) method was the primary analysis in this analysis. We used the MR-Egger method to determine horizontal pleiotropic in this work. The heterogeneity effect of instrumental IVs was detected by MR-Egger and IVW analyses. Sensitivity analysis was performed by removing single nucleotide polymorphism (SNP) one by one. Three SNPs (rs964184, rs2108622, and rs11057830) (P < 5E−8) strongly associated with circulating alpha-tocopherol levels were used in this analysis. The IVW-random effect indicated no causal relationship between circulating alpha-tocopherol levels and clinically diagnosed OA (OR = 0.880, 95% CI 0.626, 1.236, P = 0.461). Similarly, IVW analysis showed no causal association between circulating alpha-tocopherol levels and self-reported OA (OR = 0.980, 95% CI 0.954, 1.006, P = 0.139). Other methods of MR analyses and sensitivity analyses revealed consistent findings. MR-Egger and IVW methods indicated no significant heterogeneity between IVs. The MR–Egger intercept showed no horizontal pleiotropic. The results of this linear Mendelian randomization study indicate no causal association between genetically predicted alpha-tocopherol levels and the progression of OA. Alpha-tocopherol may not provide beneficial and more favorable outcomes for the progression of OA. Further MR analysis based on updated GWASs with more IVs is required to verify the results of our study.

BackgroundThe 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.MethodsTwo-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.ResultsUsing 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.ConclusionsThe 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.

ObjectivesPrevious observational studies have suggested associations between concentrations of several circulating micronutrients and sarcopenia. However, the causality inferred from those studies was subjected to residual confounding and reverse causation. Therefore, we aimed to examine the causal effects of the levels of genetically predicted serum micronutrients on sarcopenia.MethodsSingle nucleotide polymorphisms (SNPs) were chosen from large-scale genome-wide association studies of participants only with European descent and were used as genetic instruments for the levels of 10 serum micronutrients (calcium, magnesium, selenium, copper, iron, zinc, Vitamin A, Vitamin B12, Vitamin D, and Vitamin E). Sarcopenia was defined by referencing to the 2019 definition given by the European Working Group on Sarcopenia in Older People (EWGSOP). A two-sample Mendelian randomization (MR) analysis was carried out to examine the associations between the levels of genetically predicted serum micronutrients and the risk of sarcopenia. Then, sensitivity analyses (including weighted median, MR-Egger and leave-one-out sensitivity analyses) were performed to evaluate the robustness of study findings. The estimates were presented as odds ratio (OR) with their 95% confidence intervals (CIs) per one standard deviation (SD) increase in the exposures.ResultsA total of 378,635 UK Biobank participants, including 572 participants who were identified with sarcopenia, were included in this study. The iron status was shown to have a clear effect on the risk of sarcopenia based on MR analyses. The per one SD increment in the genetically-determined serum iron level corresponded to a 53% increase in the risk of sarcopenia (OR = 1.53, 95% CI: 1.31–1.78, P = 0.001). The exclusion of SNPs of the circulating iron level (i.e., rs1799945 SNP, rs1800562 SNP or rs855791 SNP) did not attenuate the magnitude of the signal in MR analysis. There was little evidence supporting the associations between other remaining micronutrients and sarcopenia.ConclusionsAn increased risk of sarcopenia was observed with a genetically higher concentration of iron, suggesting that iron may play a role in the occurrence or development of sarcopenia.

BackgroundChronic Obstructive Pulmonary Disease (COPD) currently ranks as the third leading cause of mortality worldwide, imposing substantial burdens on societal and individual health. Amongst health research tools, walking pace (WP) and hand grip strength (HGS) are cornerstones, extensively associated with diverse health conditions. However, the intricate interplay between these factors and COPD risk remains ambiguous. This study aims to elucidate the causal association of WP, HGS, with COPD risk through a bidirectional Mendelian randomization (MR) approach.MethodsBidirectional MR analysis was performed using Genome-wide association study (GWAS) data of European individuals for WP, HGS, and COPD. Inverse Variance Weighted (IVW) served as the primary MR analysis approach. To supplement the IVW findings, four additional MR methods [MR-Egger, weighted median, maximum likelihood, simple median] were used. To assess heterogeneity and pleiotropy, sensitivity analyses were performed. In addition, multivariate MR (MVMR) analysis was used to assess causality after adjustment for potential confounders.ResultsIVW method results show a significant negative association between WP and COPD risk in both initial (genome-wide threshold, odds ratio (OR) = 0.21, 95% confidence interval (CI) 0.09–0.51, P = 5.06 × 10− 4) and secondary (locus-wide threshold, OR = 0.27, 95%CI: 0.18–0.41, P = 4.88 × 10− 10) MR analysis. The reverse MR analysis suggested that COPD also diminishes WP. Additionally, a causal risk reduction for COPD with right HGS (OR = 0.74, 95% CI: 0.58–0.94, P = 1.44 × 10− 2) was only found in secondary MR analysis. The outcomes of the four additional MR methods also suggested similar causal relationships, and sensitivity analyses endorsed their robustness. Lastly, the MVMR analysis demonstrated that the WP’s effect on reducing COPD risk persisted independently of potential confounding variables.ConclusionA bidirectional causal relationship exists between typical WP and COPD risk. Conversely, a decrease in right HGS is unidirectionally associated with an increased risk of COPD. The study suggests that WP may serve as a predictive factor for COPD or as a simple evaluative indicator for prognosis.

BackgroundAlthough anxiety disorders are one of the most prevalent mental disorders, their underlying biological mechanisms have not yet been fully elucidated. In recent years, genetically determined metabolites (GDMs) have been used to reveal the biological mechanisms of mental disorders. However, this strategy has not been applied to anxiety disorders. Herein, we explored the causality of GDMs on anxiety disorders through Mendelian randomization study, with the overarching goal of unraveling the biological mechanisms.MethodsA two-sample Mendelian randomization (MR) analysis was implemented to assess the causality of GDMs on anxiety disorders. A genome-wide association study (GWAS) of 486 metabolites was used as the exposure, whereas four different GWAS datasets of anxiety disorders were the outcomes. Notably, all datasets were acquired from publicly available databases. A genetic instrumental variable (IV) was used to explore the causality between the metabolite and anxiety disorders for each metabolite. The MR Steiger filtering method was implemented to examine the causality between metabolites and anxiety disorders. The standard inverse variance weighted (IVW) method was first used for the causality analysis, followed by three additional MR methods (the MR-Egger, weighted median, and MR-PRESSO (pleiotropy residual sum and outlier) methods) for sensitivity analyses in MR analysis. MR-Egger intercept, and Cochran’s Q statistical analysis were used to evaluate possible heterogeneity and pleiotropy. Bonferroni correction was used to determine the causative association features (P < 1.03 × 10–4). Furthermore, metabolic pathways analysis was performed using the web-based MetaboAnalyst 5.0 software. All statistical analysis were performed in R software. The STROBE-MR checklist for the reporting of MR studies was used in this study.ResultsIn MR analysis, 85 significant causative relationship GDMs were identified. Among them, 11 metabolites were overlapped in the four different datasets of anxiety disorders. Bonferroni correction showing1-linoleoylglycerophosphoethanolamine (ORfixed-effect IVW = 1.04; 95% CI 1.021–1.06; Pfixed-effect IVW = 4.3 × 10–5) was the most reliable causal metabolite. Our results were robust even without a single SNP because of a “leave-one-out” analysis. The MR-Egger intercept test indicated that genetic pleiotropy had no effect on the results (intercept = − 0.0013, SE = 0.0006, P = 0.06). No heterogeneity was detected by Cochran’s Q test (MR-Egger. Q = 7.68, P = 0.742; IVW. Q = 12.12, P = 0.436). A directionality test conducted by MR Steiger confirmed our estimation of potential causal direction (P < 0.001). In addition, two significant pathways, the “primary bile acid biosynthesis” pathway (P = 0.008) and the “valine, leucine, and isoleucine biosynthesis” pathway (P = 0.03), were identified through metabolic pathway analysis.ConclusionThis study provides new insights into the causal effects of GDMs on anxiety disorders by integrating genomics and metabolomics. The metabolites that drive anxiety disorders may be suited to serve as biomarkers and also will help to unravel the biological mechanisms of anxiety disorders.

Numerous observational studies have found a relationship between systemic lupus erythematosus (SLE) and epilepsy; however, their causal relationship remains unclear. This study aimed to investigate the causal role of SLE in epilepsy or any of its subtypes using a two-sample Mendelian randomization (MR) analysis. Single nucleotide polymorphisms (SNPs) linked to SLE were utilized as instrumental variables in MR analysis to assess their causal impact on epilepsy. The primary MR findings were derived using the inverse variance weighted (IVW) method, which was further supported by the weighted median and MR-Egger regression techniques. Additionally, sensitivity analyses, including Cochran's Q test and pleiotropy tests, were conducted to evaluate the influence of these SNPs on epilepsy, particularly looking for signs of horizontal pleiotropy and heterogeneity. We selected 43 SNPs that reached genome-wide significance from genome-wide association studies (GWASs) on SLE to serve as instrumental variables in this study. The IVW method showed no evidence to support a causal association between SLE and epilepsy (all epilepsy: odds ratio (OR) = 1.006, 95% confidence interval (CI) = 0.994-1.018; focal epilepsy: OR = 1.006, 95% CI = 0.994-1.019; generalized epilepsy: OR = 1.015, 95% CI = 0.996-1.035). Other MR complementary methods revealed consistent results. Furthermore, there was no evidence indicating heterogeneity or horizontal pleiotropy. The findings of MR analysis did not support a genetically predicted causal relationship between SLE and epilepsy, but emphasized the need for further research on shared pathophysiological mechanisms, particularly the role of immune system abnormalities and potential influences such as chronic inflammation and therapeutic interventions. The etiology of epilepsy is complex and diverse, including immune factors. Through a Mendelian randomization analysis, we did not find evidence of a genetic causal relationship between systemic lupus erythematosus and epilepsy. However, this does not invalidate epidemiological evidence, and further exploration is needed to investigate factors influencing the relationship between the two.

In recent years, the incidence rates of rheumatoid arthritis (RA) and heart disease (HD) have noticeably increased worldwide. Previous studies have found that patients with RA are more likely to develop HD, while the cause and effect have still remained elusive. In this study, Mendelian randomization (MR) analysis was used to indicate whether there was a potential association between RA and HD. Data of RA, ischemic heart disease (IHD), myocardial infarction (MI), atrial fibrillation (AF), and arrhythmia were based on the genome-wide association study (GWAS) dataset. No disease group was intersected. Inverse-variance weighted (IVW) method was used to calculate MR estimates, and sensitivity analysis was performed. The primary MR analysis showed that genetic susceptibility to RA was significantly associated with the risk of IHD and MI, rather than with AF and arrhythmia. Besides, there was no heterogeneity and horizontal pleiotropy between the primary and replicated analyses. There was a significant correlation between RA and the risk of IHD (odds ratio (OR), 1.0006; 95% confidence interval (CI), 1.000244-1.00104; P = 0.001552), meanwhile, there was a significant correlation between RA and the risk of MI (OR, 1.0458; 95% CI, 1.07061-1.05379; P = 0.001636). The results were similar to those of sensitivity analysis, and the sensitivity analysis also verified the conclusion. Furthermore, sensitivity and reverse MR analyses suggested that no heterogeneity, horizontal pleiotropy or reverse causality was found between RA and cardiovascular comorbidity. RA was noted to be causally associated with IHD and MI, rather than with AF and arrhythmia. This MR study might provide a new genetic basis for the causal relationship between RA and the risk of CVD. The findings suggested that the control of RA activity might reduce the risk of cardiovascular disease.

Background: In observational studies, the self-reported walking pace has been associated with the risk of cardiovascular diseases (CVD). However, whether those associations indicate causal links remains unclear. We performed two-sample Mendelian randomization (MR) analyses to evaluate the causal effect of walking pace on several CVD outcomes, including atrial fibrillation (AF), heart failure (HF), any stroke, ischemic stroke (IS), and IS subtypes. Methods: Genetic variants associated with self-reported walking pace were selected as instrumental variables (IVs) from the latest genome-wide association studies (GWAS). Summary-level data for outcomes were obtained from the corresponding GWAS and the FinnGen consortium. The random-effects inverse variance weighted (IVW) method was used as the main MR analysis, supplemented by replication analyses using data from the FinnGen. To explore the effect of pleiotropy due to adiposity-related traits, we further conducted MR analyses by excluding the adiposity-related IVs and regression-based multivariable MR adjusting for body mass index (BMI). Results: The MR results indicated significant inverse associations of self-reported walking pace with risks of AF [odds ratio (OR), 0.577; 95% confidence interval (CI), 0.442, 0.755; p = 5.87 × 10−5], HF (OR, 0.307; 95% CI, 0.229, 0.413; p = 5.31 × 10−15), any stroke (OR, 0.540; 95% CI, 0.388, 0.752; p = 2.63 × 10−4) and IS (OR, 0.604; 95% CI, 0.427, 0.853; p = 0.004) and suggestive inverse association of self-reported walking pace with cardioembolic stroke (CES) (OR, 0.492; 95% CI, 0.259, 0.934; p = 0.030). Similar results were replicated in the FinnGen consortium and persisted in the meta-analysis. However, there was no causality between walking pace and large artery stroke (OR, 0.676; 95% CI, 0.319, 1.434; p = 0.308) or small vessel stroke (OR, 0.603; 95% CI, 0.270, 1.349; p = 0.218). When excluding adiposity-related IVs and adjusting for BMI, the associations for HF and any stroke did not change substantially, whereas the associations for AF, IS, and CES were weakened. Conclusion: Our findings suggested that genetically predicted increasing walking pace exerted beneficial effects on AF, HF, any stroke, IS, and CES. Adiposity might partially mediate the effect of walking pace on AF, IS, and CES.

Pernicious anaemia (PA) is characterised by vitamin B12 deficiency due to autoimmune-mediated destruction of gastric parietal cells and the consequent loss of intrinsic factor, a specific transporter for the intestinal uptake of vitamin B12. The aetiology of PA remains largely unknown, although genetic and environmental factors have been proposed to underpin the onset of PA(1). A significant proportion of PA patients exhibit iron deficiency, with approximately 50% of PA patients presenting with it before or at diagnosis and 61% subsequently, suggesting an association between the two(2). However, findings from traditional epidemiological studies are subject to confounding and reverse causality. For instance, these associations do not clarify whether iron deficiency contributes to the development of PA or is a consequence of the disease process. Given the profound prevalence of iron deficiency at diagnosis, we hypothesised that reduced iron levels may play a causal role in the onset of PA. We used a Mendelian randomisation (MR) approach to test the causal relationship between iron status and PA.MR leverages the naturally randomised allocation of genetic variants among the population as instrumental variables to gauge the causal effect of an exposure on an outcome of interest(3). We conducted two-sample MR analyses to assess the association between genetically predicted iron levels and PA risk. We obtained genetic association data on iron status from the deCODE study(4). PA genetic association data was sourced from the R10 release of Finngen as our main analysis. The participant data consisted of 3,694 cases of PA and 393,684 controls. Our primary MR analysis method was the inverse-variance weighted approach with additional sensitivity analyses, including leave-one-out, Egger and weighted median analyses.Four single nucleotide polymorphisms (SNPs) were strongly associated with systemic iron status and used as genetic instruments to proxy iron status in two-sample MR analyses. We found that genetically predicted higher iron status was not significantly associated with risk of PA (odds ratio per 1 standard deviation increase in serum iron: 1.12, 95% confidence interval 0.80 to 1.57, P = 0.49). Sensitivity analyses had consistent results, indicating that MR assumptions were not violated and that no single SNP drove the association.This is the first study to test the hypothesis that iron deficiency is causally associated with an increased risk of PA. Our results show that genetically predicted lower iron levels were not associated with an increased risk of PA among individuals of Finnish ancestry. Further investigation is required to understand the manifestation of iron deficiency in PA. Iron deficiency may only be a consequence of PA due to the loss of parietal cells, which produce hydrochloric acid necessary for iron absorption. The frequent presence of iron deficiency before or at diagnosis may also reflect delays in diagnosing PA.

This study sought to investigate the causal effects of circulating C-reactive protein (CRP) level on risk of asthma and its subtypes by two-sample Mendelian randomization (MR) analysis. We utilized single nucleotide polymorphisms (SNPs) associated with both CRP and outcomes of asthma, allergic asthma, and obesity-related asthma as genetic variables via a genome-wide summary association study (GWAS). MR analysis mainly based on the inverse variance weighted (IVW) method was performed to infer the causal relationship between exposure and outcomes. Cochran's Q test and MR-Egger regression analysis were performed to determine respectively the heterogeneity and pleiotropy among instrumental variables (IVs), and leave-one-out analysis was conducted to determine the stability of the MR results. In our study, 42 SNPs were identified as IVs for MR analyses. According to the primary inference results by IVW methods, circulating CRP was demonstrated to be significantly associated with risk of asthma [odds ratio (OR):1.046; 95% confidence interval (95% CI): 1.004-1.090; P = .030] and obesity-related asthma (OR:1.072; 95% CI: 1.009-1.138; P = 0.025), whereas no distinct causality with allergic asthma was found (OR:1.051; 95% CI: 0.994-1.112; P = .081). Sensitivity analyses indicated that there was no horizontal pleiotropy among IVs, and the MR results were proved to be robust by leave-one-out sensitivity analysis, despite the presence of heterogeneity. The present study suggested that higher CRP might genetically predict an increased risk of developing asthma and obesity-related asthma, without causality with allergic asthma.