Are Mendelian randomization investigations immune from bias due to reverse causation?

Serum uric acid levels and intracerebral hemorrhage: A two-sample Mendelian randomization study

OBJECTIVE

Previous observational studies have generated controversy regarding the correlation between serum uric acid (UA) levels and intracerebral hemorrhage (ICH), with the causal relationship remaining uncertain. To assess the potential causal relationship between serum UA levels and ICH, two-sample Mendelian randomization analysis was applied.

METHODS

Single-nucleotide polymorphisms (SNPs) closely associated with serum UA were retrieved from the genome-wide association study (GWAS) database, including 580,505 individuals of European descent. A total of 27 and 251 SNPs were chosen as instrumental variables. Summary data for ICH included 1935 cases and 471,578 controls. Two-sample MR analyses, including inverse-variance weighted (IVW), MR-Egger, weighted median, and weighted mode methods, were employed to assess the potential causal relationship between serum UA levels and ICH, with odds ratios (ORs) as effect estimates. Heterogeneity was evaluated using Cochran's Q test, and sensitivity analyses were conducted using the leave-one-out method.

RESULTS

The IVW analysis revealed that a 1 mg/dL increase in serum UA was associated with a 16.5 % higher risk of ICH (OR 1.165, 95 % CI 1.01-1.34, P = 0.034), while a 1 quantile increase in serum UA was associated with a 25.9 % higher risk (OR 1.259, 95 % CI 1.091-1.46, P = 0.002). Cochran's Q test showed no evidence of heterogeneity. No horizontal pleiotropy was detected. The sensitivity analysis using the leave-one-out method supported the robustness and reliability of our results.

CONCLUSION

The study reveals that elevated serum UA levels are causally linked to ICH, suggesting the potential applicability of serum UA as a biomarker for the occurrence of ICH.

The causal effects of 2,821 protein level ratios on non-small cell lung cancer: a two-sample Mendelian randomization study

Background

Non-small cell lung cancer (NSCLC) has a complex etiology, making early diagnosis difficult and leading to high mortality rates, thus necessitating personalized treatment strategies. While protein level ratios have shown potential as biomarkers or therapeutic targets, their causal relationship with NSCLC remains unclear. This study aimed to investigate these causal links using Mendelian randomization (MR), providing insights into potential biomarkers and therapeutic avenues.

Methods

We executed an intricate two-sample MR study to explore the stochastic causal links between 2,821 protein level ratios and NSCLC. The genome-wide association study (GWAS) statistics for NSCLC and protein level ratios were sourced from the Finnish Database (version 10) and the UK Biobank, respectively. For the instrumental variables (IVs) related to protein level ratios, we selected IVs with a P value <1.0×10-5. Throughout this analysis, we applied five established MR techniques.

Results

Our study identified causal relationships between 142 protein level ratios and NSCLC. Notably, the AKR1B1/SUGT1 protein level ratio and the PLPBP/STIP1 protein level ratio demonstrated the most significant negative correlations with NSCLC risk. On the other hand, the ARHGEF12/IRAK4 protein level ratio and the BANK1/LBR protein level ratio exhibited the most significant positive correlations. Furthermore, sensitivity analyses did not reveal any significant heterogeneity or horizontal pleiotropy.

Conclusions

Studying specific protein level ratios in patients can reveal the molecular mechanisms and pathological processes of NSCLC, which has certain clinical significance for early diagnosis of NSCLC, understanding drug resistance mechanisms and developing personalized treatment strategies. However, these findings necessitate further validation through extensive clinical research.

Genetically predicted inflammatory proteins mediate the association between gut microbiota and renal cell carcinoma

BACKGROUND

Studies have indicated a potential relationship between gut microbiota and renal cell carcinoma. However, the causal relationship between various types of gut microbiota and renal cell carcinoma, as well as the role of inflammatory protein as mediators, remains unclear.

METHODS

This study aimed to identify the relationship between gut microbiota, inflammatory protein, and renal cell cancer through a large-scale genome-wide association study (GWAS) utilizing pooled data. We employed Mendelian randomization (MR) to investigate the causal relationship among these variables. Inverse variance weighting (IVW) was utilized as the primary statistical method. Furthermore, we examined the mediating role of inflammatory protein in the pathway through which gut microbiota influences the development of renal cell cancer.

RESULTS

The analysis revealed 12 positive causal relationships and 15 negative causal relationships between the genetic liability of gut microbiota and renal cell cancer. Furthermore, there were three positive causal relationships and one negative causal relationship between inflammatory proteins and renal cell cancer. There were two axes of relationships in which gut microbiota promote the development of renal cell cancer. through inflammatory proteins acting as mediators.

CONCLUSIONS

Gut microbiota and inflammatory protein were causally related to renal cell cancer, and inflammatory protein were intermediary factors in the pathway between gut microbiota and renal cell cancer.

Adiponectin and Risk of Psoriasis: Observational and Mendelian Randomization Studies in up to 900 000 Individuals

BACKGROUND

Psoriasis is a chronic inflammatory skin disorder often associated with obesity. Adiponectin, an anti-inflammatory protein-hormone secreted by adipose tissue, may be a link between obesity and psoriasis. We hypothesized that low plasma adiponectin is associated with an increased risk of psoriasis in observational and causal genetic studies.

METHODS

In observational analyses, we used information on plasma adiponectin and psoriasis in 30 045 individuals from the Copenhagen General Population Study (CGPS). In one-sample Mendelian randomization analyses, we used genetic information on adiponectin and psoriasis in 107 308 individuals from the CGPS. In two-sample Mendelian randomization analyses, we used genetic information on adiponectin from the ADIPOGen consortium and genetic information on psoriasis in 373 338 and 462 933 individuals from the FinnGen study and UK Biobank (UKB).

RESULTS

In observational analyses, a 1-unit log-transformed higher plasma adiponectin was associated with a hazard ratio (HR) for psoriasis of 0.67 (95% confidence interval: 0.48-0.94) in an age- and sex-adjusted model but not in a multivariable adjusted model including obesity measures with a HR of 0.95 (0.66-1.35). In genetic one-sample Mendelian randomization analysis, a 1-unit log-transformed higher plasma adiponectin was not associated with a causal risk ratio for psoriasis of 1.33 (0.77-2.32) in the CGPS. In two-sample Mendelian randomization analyses, a 1-unit log-transformed higher plasma adiponectin was not associated with causal risk ratios for psoriasis of 0.96 (0.81-1.14) in FinnGen and 1.00 (1.00-1.01) in UKB.

CONCLUSIONS

Low plasma adiponectin is associated with increased risk of psoriasis in age- and sex-adjusted observational analyses; however, this was not the case after adjustment for obesity measures or in causal genetic analyses.

Insights into drug adverse reactions prediction through Mendelian randomization: a review

Adverse drug reactions pose a significant threat to patient safety and public health and often become apparent only after widespread clinical use. Mendelian randomization (MR) analysis is a valuable tool that can be used to infer causality by using genetic variants as instrumental variables, which can predict the occurrence of adverse drug reactions before they occur. Compared with traditional observational studies, MR Analysis can reduce the potential bias of confounding factors. This article reviews the principles of MR Analysis and its application in the prediction of adverse drug reactions, the challenges and future directions, and summarizes how to harness the power of this innovative epidemiological method to put us at the forefront of improving drug safety assessment and personalized medicine.

Autoimmune diseases and cardiovascular risk: Mendelian randomization analysis for the impact of 19 autoimmune diseases on 14 cardiovascular conditions

Backgroud

Autoimmune diseases (AIDs) have been associated with various cardiovascular diseases (CVDs) in observational data. However, the causality of these associations remains uncertain. Therefore, a systematic assessment of the impact of AIDS on cardiovascular risk is required.

Results

We assessed the impact of 19 common AIDs on 14 CVDs using bidirectional Mendelian randomization (MR). Celiac disease (odds ratio [OR] = 2.949, 95 % confidence interval [CI]: 1.111-7.827, P = 0.030) and type 1 diabetes mellitus (T1DM) (OR = 1.044, 95 % CI: 1.021-1.068, P = 1.82e-4) were associated with an increased risk of peripheral arterial disease (PAD). Additionally, celiac disease was linked to an increased risk of arrhythmia (OR = 1.008, 95 % CI: 1.002-1.013, P = 0.004), multiple sclerosis to venous thromboembolism (OR = 1.001, 95 % CI: 1.000-1.001, P = 0.010), and psoriasis to heart failure (OR = 1.048, 95 % CI: 1.021-1.077, P = 0.001). Sensitivity analyses were conducted to enhance the robustness of these findings. Predominantly, immune response and inflammation-related pathways were enriched in the aforementioned associations. Mediation analysis identified human leukocyte antigen-DR positive myeloid dendritic cells as partially mediating the effect of T1DM on PAD, with a mediated proportion of 16.61 % (P = 0.028). Potential therapeutic agents, such as tumor necrosis factor-alpha inhibitors and interferon, may have efficacy in treating AID-related CVDs.

Conclusions

This study presents genetic evidence of certain AIDs impacting specific CVDs and identifies potential mediators and drugs.

Genetically Supported Drug Targets and Dental Traits: A Mendelian Randomization Study

Current interventions for oral/dental diseases heavily rely on operative/surgical procedures, while the discovery of novel drug targets may enable access to noninvasive pharmacotherapy. Therefore, this study aims to leverage large-scale data and Mendelian randomization (MR) techniques, utilizing genetic variants as instruments, to identify potential therapeutic targets for oral and dental diseases supported by genetic evidence. By intersecting 4,302 druggable genes with expression quantitative trait loci from 31,684 blood samples, we identified 2,580 druggable targets as exposures. Single nucleotide polymorphisms associated with dental disease/symptom traits were collected from FinnGen R9, the Gene-Lifestyle Interactions in Dental Endpoints consortium, and the UK Biobank to serve as outcomes for both discovery and replication purposes. Through MR analysis, we identified 43 druggable targets for various dental disease/symptom traits. To evaluate the viability of these targets, we replicated the analysis using circulating protein quantitative trait loci as exposures. Additionally, we conducted sensitivity, colocalization, Gene Ontology/Kyoto Encyclopedia of Genes and Genomes annotation, protein-protein interaction analyses, and validated dental trait-associated druggable gene expression in animal models. Among these targets, IL12RB1 (odds ratio [OR], 1.01; 95% confidence interval [CI], 1.01-1.01) and TNF (OR, 0.98; 95% CI, 0.97-0.99) exhibited therapeutic promise for oral ulcers, whereas CXCL10 (OR, 0.84; 95% CI, 0.76-0.91) was for periodontitis. Through a rigorous quality control and validation pipeline, our study yields compelling evidence for these druggable targets, which may enhance the clinical prognosis by developing novel drugs or repurposing existing ones.

Evidence of the association between asthma and lung cancer risk from mendelian randomization analysis

Asthma and lung cancer are both significant public health concerns worldwide. Previous observational studies have indicated a potential link between asthma and an increased risk of lung cancer, whereas the causal relationship remains uncertain. We aimed to investigate the potential causal relationship between asthma and lung cancer risk utilizing Mendelian randomization (MR) design.The present study employed a two-sample MR analysis utilizing summary statistics from genome-wide association studies (GWAS) with European descent of asthma and lung cancer. The MR analysis was performed using inverse variance weighting (IVW), supplemented with MR-Egger regression and weighted median method to investigate the potential causality between asthma and lung cancer. Furthermore, Sensitivity analyses were also conducted to ensure the reliability of the findings. The MR analysis showed that genetically predicted asthma had suggestive causal association with the elevated risk of lung cancer [odds ratio (OR), 1.05 (95%Cl,1.01-1.09), P = 0.01]. The consistent direction of effects observed in the three methods further supported this finding. In addition, sensitivity analyses demonstrated the reliability of the results. This study provided potential evidence supporting a causal association between asthma and lung cancer. These findings highlighted the importance of early detection and prevention strategies for lung cancer in individuals with asthma. Further research was needed to elucidate the underlying mechanisms linking asthma and lung cancer.

Mendelian randomization studies of periodontitis: Understanding benefits and natural limitations in an applied context

Mendelian randomization (MR) is a flexible analytical tool that has been widely applied to strengthen causal inference in observational epidemiology and is now gaining attention in many areas including periodontal research. The interpretation of results drawn from MR is based on a series of assumptions, which can be unrealistic or difficult to meet faithfully in some settings. However, we argue that with care, this does not necessarily prevent valuable deployment of the approach. We argue that clarity of presentation as well as careful assessment of specific analytical conditions is a fundamental part of all MR analyses. To that end, awareness of its limitations should also guide the design of MR investigations and the presentation of results rather than rule out its use altogether. Notably, considerations similar to those known to be important in conventional epidemiological settings apply to MR. While MR studies are valuable in their contrast to other study limitations, the application of this technique must be carefully cross-examined. Specific considerations include possible confounders, recruitment strategy and phenotypic measurement and differential analysis properties across studies. In the case of periodontal research, current MR applications are limited by the available evidence base for genetic contributions to periodontitis; however, this sets a specific scene for the strategic use of MR and shines light on a need for greater research emphasis on the genetics of the condition and intermediaries. This article provides a perspective on the uses and inherent limitations of MR studies and the importance of adhering to basic epidemiological principles when designing them.

Investigation of the causal relationship between cholelithiasis and Parkinson's disease: A bidirectional Mendelian randomization study

Background

Parkinson's disease (PD) and cholelithiasis are a huge public health burden. Although observational studies have suggested a potential link between PD and cholelithiasis, the causal relationship between the two remains uncertain. To address this gap, we performed a two-sample bidirectional Mendelian randomization analysis using genetic tools.

Method

Genome-wide association study summary statistics for all traits were obtained from publicly available databases. We used strict control steps in instrumental variable selection to screen for single nucleotide polymorphisms (SNPs) from summary-level genome-wide association studies. In addition, all F-statistics were >10, indicating no weak instrumental bias. The inverse variance weighting (IVW) method was the primary method used to assess causal associations. Four other MR methods (MR-Egger, Weighted Median, Simple mode, and Weighted mode) were also used to complement IVW. Various sensitivity tests were also performed to assess reliability: (1) Cochrane's Q test for assessing heterogeneity, (2) MR-Egger intercept test and MR-PRESSO global test for assessing horizontal multiplicity, and (3) leave-one-out sensitivity test for determining stability.

Results

We selected a total of 30 SNPs as instrumental variables. It was demonstrated that cholelithiasis had a causal effect on the risk of PD (OR = 1.146, 95% CI: 1.062-1.236, p < 0.001) in IVW method.

Conclusion

The results of our analysis revealed an increased risk effect of cholelithiasis against PD, which may give light on new approaches to PD prevention and therapy.

Trans-ancestry analysis in over 799,000 individuals yields new insights into the genetic etiology of colorectal cancer

BACKGROUND

Recent studies have demonstrated the relevance of circulating factors in the occurrence and development of colorectal cancer (CRC); however, the causal relationship remains unclear.

METHODS

Summary-level data for CRC were obtained from the UK Biobank (5,657 cases and 372,016 controls), FinnGen cohort (3,022 cases and 215,770 controls), and BioBank Japan Project (BBJ, 7,062 cases and 195,745 controls). Thirty-two peripheral markers with consistent definitions were collected from the three biobanks. Mendelian randomization (MR) was used to evaluate the causal effect of circulating factors on CRC. The effects from the three consortiums were combined using trans-ancestry meta-analysis methods.

RESULTS

Our analysis provided compelling evidence for the causal association of higher genetically predicted eosinophil cell count (EOS, odds ratio [OR], 0.8639; 95% confidence interval [CI] 0.7922-0.9421) and red cell distribution width (RDW, OR, 0.9981; 95% CI, 0.9972-0.9989) levels with a decreased risk of CRC. Additionally, we found suggestive evidence indicating that higher levels of total cholesterol (TC, OR, 1.0022; 95% CI, 1.0002-1.0042) may increase the risk of CRC. Conversely, higher levels of platelet count (PLT, OR, 0.9984; 95% CI, 0.9972-0.9996), total protein (TP, OR, 0.9445; 95% CI, 0.9037-0.9872), and C-reactive protein (CRP, OR, 0.9991; 95% CI, 0.9983-0.9999) may confer a protective effect against CRC. Moreover, we identified six ancestry-specific causal factors, indicating the necessity of considering patients' ancestry backgrounds before formulating prevention strategies.

CONCLUSIONS

MR findings support the independent causal roles of circulating factors in CRC, which might provide a deeper insight into early detection of CRC and supply potential preventative strategies.

Vitamin D, chronic pain, and depression: linear and non-linear Mendelian randomization analyses

Vitamin D deficiency has been linked to various chronic pain conditions. However, randomized trials of vitamin D supplementation have had mixed results. In contrast, systematic reviews of randomized trials indicate a protective effect of vitamin D supplementation on depression. We undertake a Mendelian randomization investigation in UK Biobank, a study of UK residents aged 40-65 at recruitment. We perform linear and non-linear Mendelian randomization analyses for four outcomes: fibromyalgia, clinical fatigue, chronic widespread pain, and probable lifetime major depression. We use genetic variants from four gene regions with known links to vitamin D biology as instruments. In linear analyses, genetically-predicted levels of 25-hydroxyvitamin D [25(OH)D], a clinical marker of vitamin D status, were not associated with fibromyalgia (odds ratio [OR] per 10 nmol/L higher 25(OH)D 1.02, 95% confidence interval [CI] 0.93, 1.12), clinical fatigue (OR 0.99, 95% CI 0.94, 1.05), chronic widespread pain (OR 0.95, 95% CI 0.89, 1.02), or probable lifetime major depression (OR 0.97, 95% CI 0.93, 1.01). In non-linear analyses, an association was observed between genetically-predicted 25(OH)D levels and depression in the quintile of the population with the lowest 25(OH)D levels (OR 0.75, 95% CI 0.59, 0.94); associations were null in other strata. Our findings suggest that population-wide vitamin D supplementation will not substantially reduce pain or depression; however, targeted supplementation of deficient individuals may reduce risk of depression.

Mendelian randomization: causal inference leveraging genetic data

Mendelian randomization (MR) leverages genetic information to examine the causal relationship between phenotypes allowing for the presence of unmeasured confounders. MR has been widely applied to unresolved questions in epidemiology, making use of summary statistics from genome-wide association studies on an increasing number of human traits. However, an understanding of essential concepts is necessary for the appropriate application and interpretation of MR. This review aims to provide a non-technical overview of MR and demonstrate its relevance to psychiatric research. We begin with the origins of MR and the reasons for its recent expansion, followed by an overview of its statistical methodology. We then describe the limitations of MR, and how these are being addressed by recent methodological advances. We showcase the practical use of MR in psychiatry through three illustrative examples - the connection between cannabis use and psychosis, the link between intelligence and schizophrenia, and the search for modifiable risk factors for depression. The review concludes with a discussion of the prospects of MR, focusing on the integration of multi-omics data and its extension to delineating complex causal networks.

Body mass index and all-cause mortality in HUNT and UK biobank studies: revised non-linear Mendelian randomisation analyses

OBJECTIVES

To estimate the shape of the causal relationship between body mass index (BMI) and mortality risk in a Mendelian randomisation framework.

DESIGN

Mendelian randomisation analyses of two prospective population-based cohorts.

SETTING

Individuals of European ancestries living in Norway or the UK.

PARTICIPANTS

56 150 participants from the Trøndelag Health Study (HUNT) in Norway and 366 385 participants from UK Biobank recruited by postal invitation.

OUTCOMES

All-cause mortality and cause-specific mortality (cardiovascular, cancer, non-cardiovascular non-cancer).

RESULTS

A previously published non-linear Mendelian randomisation analysis of these data using the residual stratification method suggested a J-shaped association between genetically predicted BMI and mortality outcomes with the lowest mortality risk at a BMI of around 25 kg/m2. However, the 'constant genetic effect' assumption required by this method is violated. The reanalysis of these data using the more reliable doubly-ranked stratification method provided some indication of a J-shaped relationship, but with much less certainty as there was less precision in estimates at the lower end of the BMI distribution. Evidence for a harmful effect of reducing BMI at low BMI levels was only present in some analyses, and where present, only below 20 kg/m2. A harmful effect of increasing BMI for all-cause mortality was evident above 25 kg/m2, for cardiovascular mortality above 24 kg/m2, for cancer mortality above 30 kg/m2 and for non-cardiovascular non-cancer mortality above 26 kg/m2. In UK Biobank, the association between genetically predicted BMI and mortality at high BMI levels was stronger in women than in men.

CONCLUSION

This research challenges findings from previous conventional observational epidemiology and Mendelian randomisation investigations that the lowest level of mortality risk is at a BMI level of around 25 kg/m2. Our results provide some evidence that reductions in BMI will increase mortality risk for a small proportion of the population, and clear evidence that increases in BMI will increase mortality risk for those with BMI above 25 kg/m2.

A burden of proof study on alcohol consumption and ischemic heart disease

Cohort and case-control data have suggested an association between low to moderate alcohol consumption and decreased risk of ischemic heart disease (IHD), yet results from Mendelian randomization (MR) studies designed to reduce bias have shown either no or a harmful association. Here we conducted an updated systematic review and re-evaluated existing cohort, case-control, and MR data using the burden of proof meta-analytical framework. Cohort and case-control data show low to moderate alcohol consumption is associated with decreased IHD risk - specifically, intake is inversely related to IHD and myocardial infarction morbidity in both sexes and IHD mortality in males - while pooled MR data show no association, confirming that self-reported versus genetically predicted alcohol use data yield conflicting findings about the alcohol-IHD relationship. Our results highlight the need to advance MR methodologies and emulate randomized trials using large observational databases to obtain more definitive answers to this critical public health question.

Genetic association of inflammatory marker GlycA with lung function and respiratory diseases

Association of circulating glycoprotein acetyls (GlycA), a systemic inflammation biomarker, with lung function and respiratory diseases remain to be investigated. We examined the genetic correlation, shared genetics, and potential causality of GlycA (N = 115,078) with lung function and respiratory diseases (N = 497,000). GlycA showed significant genetic correlation with FEV1 (rg = -0.14), FVC (rg = -0.18), asthma (rg = 0.21) and COPD (rg = 0.31). We consistently identified ten shared loci (including chr3p21.31 and chr8p23.1) at both SNP and gene level revealing potential shared biological mechanisms involving ubiquitination, immune response, Wnt/β-catenin signaling, cell growth and differentiation in tissues or cells including blood, epithelium, fibroblast, fetal thymus, and fetal intestine. Genetically elevated GlycA was significantly correlated with lung function and asthma susceptibility (354.13 ml decrement of FEV1, 442.28 ml decrement of FVC, and 144% increased risk of asthma per SD increment of GlycA) from MR analyses. Our findings provide insights into biological mechanisms of GlycA in relating to lung function, asthma, and COPD.

Genetic Complexities of Cerebral Small Vessel Disease, Blood Pressure, and Dementia

Importance

Vascular disease is a treatable contributor to dementia risk, but the role of specific markers remains unclear, making prevention strategies uncertain.

Objective

To investigate the causal association between white matter hyperintensity (WMH) burden, clinical stroke, blood pressure (BP), and dementia risk, while accounting for potential epidemiologic biases.

Design, Setting, and Participants

This study first examined the association of genetically determined WMH burden, stroke, and BP levels with Alzheimer disease (AD) in a 2-sample mendelian randomization (2SMR) framework. Second, using population-based studies (1979-2018) with prospective dementia surveillance, the genetic association of WMH, stroke, and BP with incident all-cause dementia was examined. Data analysis was performed from July 26, 2020, through July 24, 2022.

Exposures

Genetically determined WMH burden and BP levels, as well as genetic liability to stroke derived from genome-wide association studies (GWASs) in European ancestry populations.

Main Outcomes and Measures

The association of genetic instruments for WMH, stroke, and BP with dementia was studied using GWASs of AD (defined clinically and additionally meta-analyzed including both clinically diagnosed AD and AD defined based on parental history [AD-meta]) for 2SMR and incident all-cause dementia for longitudinal analyses.

Results

In 2SMR (summary statistics-based) analyses using AD GWASs with up to 75 024 AD cases (mean [SD] age at AD onset, 75.5 [4.4] years; 56.9% women), larger WMH burden showed evidence for a causal association with increased risk of AD (odds ratio [OR], 1.43; 95% CI, 1.10-1.86; P = .007, per unit increase in WMH risk alleles) and AD-meta (OR, 1.19; 95% CI, 1.06-1.34; P = .008), after accounting for pulse pressure for the former. Blood pressure traits showed evidence for a protective association with AD, with evidence for confounding by shared genetic instruments. In the longitudinal (individual-level data) analyses involving 10 699 incident all-cause dementia cases (mean [SD] age at dementia diagnosis, 74.4 [9.1] years; 55.4% women), no significant association was observed between larger WMH burden and incident all-cause dementia (hazard ratio [HR], 1.02; 95% CI, 1.00-1.04; P = .07). Although all exposures were associated with mortality, with the strongest association observed for systolic BP (HR, 1.04; 95% CI, 1.03-1.06; P = 1.9 × 10-14), there was no evidence for selective survival bias during follow-up using illness-death models. In secondary analyses using polygenic scores, the association of genetic liability to stroke, but not genetically determined WMH, with dementia outcomes was attenuated after adjusting for interim stroke.

Conclusions

These findings suggest that WMH is a primary vascular factor associated with dementia risk, emphasizing its significance in preventive strategies for dementia. Future studies are warranted to examine whether this finding can be generalized to non-European populations.

Evaluating the causal relationship between educational attainment and mental health

We investigate the causal relationship between educational attainment (EA) and mental health using two research designs. First, we compare the relationship between EA and 18 psychiatric diagnoses within sibship in Dutch national registry data (N=1.7 million), thereby controlling for unmeasured familial factors. Second, we apply two-sample Mendelian Randomization, which uses genetic variants related to EA or psychiatric diagnosis as instrumental variables, to test whether there is a causal relation in either direction. Our results suggest that lower levels of EA causally increase the risk of MDD, ADHD, alcohol dependence, GAD and PTSD diagnoses. We also find evidence of a causal effect of ADHD on EA. For schizophrenia, anorexia nervosa, OCD, and bipolar disorder, results were inconsistent across the different approaches, highlighting the importance of using multiple research designs to understand complex relationships such as between EA and mental health.

Mental health and lower urinary tract symptoms: Results from the NHANES and Mendelian randomization study

BACKGROUND

The clinical observations suggest a correlation between lower urinary tract symptoms (LUTSs) and mental health problems. Nonetheless, establishing a direct causal relationship between them remains challenging.

METHODS

We initially conducted a cross-sectional study using 2005-2018 the National Health and Nutrition Examination Survey (NHANES) data. Multivariable-adjusted logistic regression was the primary statistical approach. Additionally, we employed Mendelian randomization (MR) to reducing confounding and reverse causation. Genetic instruments were obtained from publicly available genome-wide association study (GWAS) databases. Inverse Variance Weighted was the primary statistical method.

RESULTS

The cross-sectional study involved 29,439 participants. Individuals with mental health problems had a higher risk of urinary incontinence (OR:4.38; 95%CI:3.32-5.76; P < 0.01) and overactive bladder (OR:2.31; 95%CI:2.02-2.63; P < 0.01). MR analysis then indicated a potential causal relationship between mental health problems and LUTSs. Depression symptoms was linked with urinary tract infection (UTI) (OR:1.005; 95%CI:1.003-1.008; PFDR < 0.01). Anxiety symptoms was related to the occurrence of UTI (OR:1.024; 95%CI:1.011-1.037; PFDR < 0.01) and bladder calcified/ contracted/ overactive (OR:1.017; 95%CI:1.007-1.027; PFDR < 0.01). The personality trait of neuroticism was related to the occurrence of cystitis (OR:1.072; 95%CI:1.022-1.125; PFDR = 0.02), extravasation of urine and difficulties with micturition (OR:1.001; 95%CI:1.001-1.002; PFDR < 0.01), and urinary frequency and incontinence (OR: 1.001; 95%CI:1.000-1.001; PFDR < 0.01).

CONCLUSIONS

Our study provides various evidence for the correlation between mental health and LUTSs, emphasizing the significance of adopting a holistic approach to LUTSs management that incorporates both physical and psychological factors.

Plasma adiponectin levels and risk of heart failure, atrial fibrillation, aortic valve stenosis, and myocardial infarction: large-scale observational and Mendelian randomization evidence

AIMS

Adiponectin may play an important protective role in heart failure and associated cardiovascular diseases. We hypothesized that plasma adiponectin is associated observationally and causally, genetically with risk of heart failure, atrial fibrillation, aortic valve stenosis, and myocardial infarction.

METHODS AND RESULTS

In the Copenhagen General Population Study, we examined 30 045 individuals with plasma adiponectin measurements observationally and 96 903 individuals genetically in one-sample Mendelian randomization analyses using five genetic variants explaining 3% of the variation in plasma adiponectin. In the HERMES, UK Biobank, The Nord-Trøndelag Health Study (HUNT), deCODE, the Michigan Genomics Initiative (MGI), DiscovEHR, and the AFGen consortia, we performed two-sample Mendelian randomization analyses in up to 1 030 836 individuals using 12 genetic variants explaining 14% of the variation in plasma adiponectin.In observational analyses modelled linearly, a 1 unit log-transformed higher plasma adiponectin was associated with a hazard ratio of 1.51 (95% confidence interval: 1.37-1.66) for heart failure, 1.63 (1.50-1.78) for atrial fibrillation, 1.21 (1.03-1.41) for aortic valve stenosis, and 1.03 (0.93-1.14) for myocardial infarction; levels above the median were also associated with an increased risk of myocardial infarction, and non-linear U-shaped associations were more apparent for heart failure, aortic valve stenosis, and myocardial infarction in less-adjusted models. Corresponding genetic, causal risk ratios were 0.92 (0.65-1.29), 0.87 (0.68-1.12), 1.55 (0.87-2.76), and 0.93 (0.67-1.30) in one-sample Mendelian randomization analyses, and no significant associations were seen for non-linear one-sample Mendelian randomization analyses; corresponding causal risk ratios were 0.99 (0.89-1.09), 1.00 (0.92-1.08), 1.01 (0.79-1.28), and 0.99 (0.86-1.13) in two-sample Mendelian randomization analyses, respectively.

CONCLUSION

Observationally, elevated plasma adiponectin was associated with an increased risk of heart failure, atrial fibrillation, aortic valve stenosis, and myocardial infarction. However, genetic evidence did not support causality for these associations.

Causal association between 637 human metabolites and ovarian cancer: a mendelian randomization study

BACKGROUND

Current evidence suggests a significant association between metabolites and ovarian cancer (OC); however, the causal relationship between the two remains unclear. This study employs Mendelian randomization (MR) to investigate the causal effects between different metabolites and OC.

METHODS

In this study, a total of 637 metabolites were selected as the exposure variables from the Genome-wide Association Study (GWAS) database ( http://gwas.mrcieu.ac.uk/datasets/ ). The OC related GWAS dataset (ieu-b-4963) was chosen as the outcome variable. R software and the TwoSampleMR package were utilized for the analysis in this study. MR analysis employed the inverse variance-weighted method (IVW), MR-Egger and weighted median (WM) for regression fitting, taking into consideration potential biases caused by linkage disequilibrium and weak instrument variables. Metabolites that did not pass the tests for heterogeneity and horizontal pleiotropy were considered to have no significant causal effect on the outcome. Steiger's upstream test was used to determine the causal direction between the exposure and outcome variables.

RESULTS

The results from IVW analysis revealed that a total of 31 human metabolites showed a significant causal effect on OC (P < 0.05). Among them, 9 metabolites exhibited consistent and stable causal effects, which were confirmed by Steiger's upstream test (P < 0.05). Among these 9 metabolites, Androsterone sulfate, Propionylcarnitine, 5alpha-androstan-3beta,17beta-diol disulfate, Total lipids in medium VLDL and Concentration of medium VLDL particles demonstrated a significant positive causal effect on OC, indicating that these metabolites promote the occurrence of OC. On the other hand, X-12,093, Octanoylcarnitine, N2,N2-dimethylguanosine, and Cis-4-decenoyl carnitine showed a significant negative causal association with OC, suggesting that these metabolites can inhibit the occurrence of OC.

CONCLUSIONS

The study revealed the complex effect of metabolites on OC through Mendelian randomization. As promising biomarkers, these metabolites are worthy of further clinical validation.

The Impact of Different Intensities of Physical Activity on Serum Urate and Gout: A Mendelian Randomization Study

Physical activity is a potential protective factor against gout, but the role of exercise intensity in this context remains unclear. To overcome the limitations of observational studies in causal inference, this study employed a two-sample Mendelian randomization approach to explore the impact of different genetically proxied/predicted intensities of physical activity on serum urate concentration and the incidence of gout. Our data related to physical activity, serum urate, and gout were obtained from the UK Biobank, the Global Urate Genetics Consortium (GUGC), and the FinnGen dataset, respectively. Walking was included as representative of typical low-intensity physical activity in the analysis, and the other two types were moderate and vigorous physical activities. The estimation methods we used included the inverse-variance-weighted (IVW) method, MR-Egger regression, weighted-median method, simple-mode method, and weighted-mode method. Sensitivity analyses involved Rucker's framework, Cochran's Q test, funnel plots, MR-PRESSO outlier correction, and leave-one-out analysis. We found suggestive evidence from the inverse-variance-weighted method that moderate physical activity was a potential factor in reducing the incidence of gout (OR = 0.628, p = 0.034), and this association became more substantial in our subsequent sensitivity analysis (OR = 0.555, p = 0.006). However, we observed no distinctive effects of physical activity on serum urate concentration. In conclusion, our study supports some findings from observational studies and emphasizes the preventive role of moderate physical activity against gout. Given the limitations of the existing datasets, we call for future reexamination and expansion of our findings using new GWAS data.

Dark chocolate intake and cardiovascular diseases: a Mendelian randomization study

Previous intervention studies have shown some benefits of dark chocolate for the cardiovascular system, but it has not been established whether dark chocolate intake is associated with the risk of cardiovascular diseases (CVDs). To investigate the causality between dark chocolate intake and the risk of CVDs, a Mendelian randomization (MR) study was conducted. We obtained summary-level data on dark chocolate intake and CVDs from publicly available genome-wide association studies. In this MR study, the main approach was to use a fixed-effect model with inverse variance weighted (IVW) and evaluate the robustness of the results via sensitivity analysis. We found that dark chocolate intake was significantly associated with the reduction of the risk of essential hypertension (EH) (OR = 0.73; 95% CI 0.60-0.88; p = 1.06 × 10-3), as well as with the suggestive association to the reduced risk of venous thromboembolism (OR = 0.69; 95% CI 0.50-0.96; p = 2.81 × 10-2). However, no association was found between dark chocolate intake and the other ten CVDs. Our study provides evidence for a causality between dark chocolate intake and a reduced risk of EH, which has important implications for the prevention of EH in the population.

Investigating the role of iron status in the development of coeliac disease: a Mendelian randomisation study

OBJECTIVE

The environmental trigger behind the increasing prevalence of coeliac disease is not known. One suggested cause is iron deficiency, which is common in coeliac disease. We aimed to evaluate this possible association with Mendelian randomisation (MR), which under certain assumptions can suggest a causal relationship.

DESIGN

We conducted a two-sample MR study examining the relationship between single nucleotide polymorphisms (SNPs) associated with iron status and the presence of coeliac disease. The SNPs were drawn from a meta-analysis of three genome-wide association studies (GWAS). The association between these SNPs and coeliac disease was assessed using GWAS summary statistics from the UK Biobank. This consists of 336 638 white British individuals, 1855 with coeliac disease. We performed an MR Egger test for pleiotropy and assessed the plausibility of the assumptions of MR to evaluate for possible causality.

RESULTS

There were four SNPs strongly associated with systemic iron status. These were not associated with known risk factors for coeliac disease. All four SNPs were available in the UK Biobank coeliac disease summary statistics. Harmonising exposure and outcome associations, we found that higher iron status was negatively associated with risk of coeliac disease (OR per 1 SD increase in serum iron: 0.65, 95% CI 0.47 to 0.91). Leave-one-out analyses had consistent results, and no single SNP drove the association. All three assumptions of MR appeared plausible.

CONCLUSION

We found that genetically lower iron levels were associated with an increased risk of coeliac disease. Our findings highlight a potential opportunity for coeliac disease prevention.

The relationship between sex hormone-binding protein and non-alcoholic fatty liver disease using Mendelian randomisation

BACKGROUND

The incidence of non-alcohol fatty liver disease (NAFLD) has been increasing annually with the improvement of living standards. Numerous epidemiological observations have linked sex hormone-binding protein (SHBG) levels to NAFLD. However, evidence of the causal role of SHBG in the development and progression of NAFLD is still absent. Therefore, a systematic assessment of the causal relationship is needed.

METHOD

A two-sample Mendelian randomisation (MR) analysis was conducted. Genome-wide association study (GWAS) data for SHBG were obtained online from the IEU database (ebi-a-GCST90012111) as exposure. GWAS data from the NAFLD of the Finngen consortium were used for preliminary analysis, while NAFLD data from another GWAS involving 8434 participants were used for replication and meta-analyses. Causal effects were investigated with inverse variance weighted (IVW), weighted median and MR-Egger regression. Sensitivity analyses including Cochran's Q test, leave-one-out analysis and MR-Egger intercept analysis were simultaneously conducted to assess heterogeneity and pleiotropy.

RESULTS

After rigorous selection, 179 single-nucleotide polymorphisms (SNPs) were identified as strongly correlated instrumental variables. Preliminary analysis suggested a significant causal relationship between genetically determined serum SHBG levels and NAFLD [odds ratio (OR) IVW  = .54, 95% confidence interval (CI) = .30-.98, p = .043], supported by the results of the replication analysis (ORIVW  = .61, 95% CI = .46-.81, p = .0006) and further meta-analysis (OR = .59, 95% CI = .46-.77, p < .0001).

CONCLUSION

The genetic tendency to high levels of SHBG was causally correlated with a reduced risk of NAFLD, indicating that circulating high levels of SHBG was a protective factor for NAFLD.

Pulmonary function and atherosclerosis in the general population: causal associations and clinical implications

Reduced lung function is associated with cardiovascular mortality, but the relationships with atherosclerosis are unclear. The population-based Swedish CArdioPulmonary BioImage study measured lung function, emphysema, coronary CT angiography, coronary calcium, carotid plaques and ankle-brachial index in 29,593 men and women aged 50-64 years. The results were confirmed using 2-sample Mendelian randomization. Lower lung function and emphysema were associated with more atherosclerosis, but these relationships were attenuated after adjustment for cardiovascular risk factors. Lung function was not associated with coronary atherosclerosis in 14,524 never-smokers. No potentially causal effect of lung function on atherosclerosis, or vice versa, was found in the 2-sample Mendelian randomization analysis. Here we show that reduced lung function and atherosclerosis are correlated in the population, but probably not causally related. Assessing lung function in addition to conventional cardiovascular risk factors to gauge risk of subclinical atherosclerosis is probably not meaningful, but low lung function found by chance should alert for atherosclerosis.

Exploring the impact of computer game playing on cognitive function, Alzheimer's disease risk, and brain-derived neurotrophic factor levels: Basic evidence from Mendelian randomization

Introduction

The potential positive impact of computer game playing on cognitive function and its potential role in reducing the risk of Alzheimer's disease (AD) has been suggested. However, current observational studies have certain limitations. We utilized Mendelian randomization (MR) alongside extensive genome-wide association study (GWAS) data to examine the relationship between computer game playing, cognitive function, risk of AD, and levels of brain-derived neurotrophic factor (BDNF).

Methods

We collected datasets on computer game playing, cognition function, risk of AD, and BDNF level from the IEU Open GWAS project. Causal effects were assessed using various MR methods, including inverse variance weighted (IVW), weighted median, MR-Egger, simple mode, and weighted mode. To ensure the accuracy of the results, sensitivity analyses were conducted.

Results

Our analysis revealed a significant association between computer game playing and cognitive function (β  =  0.801, 95% CI: 0.351, 1.328, P  =  0.001). There was no statistically significant association between computer game playing and either BDNF level or risk of AD (β  =  -0.112, 95%CI: -1.315, 1.091, P  =  0.855; OR = 1.000, 95% CI: 1.004, 0.997, P  =  0.891, respectively). We further confirmed the reliability of our evidence through the MR-Egger intercept test, MR-PRESSO global test, Cochran's Q test, and funnel plots.

Conclusion

The results of our study indicate that engaging in computer game playing may confer a safeguarding influence on cognitive function. This underscores the potential advantages associated with computer gaming. Nevertheless, given the constraints inherent in our research, further investigation is warranted to substantiate our findings and delve into the underlying mechanisms.

The causal relationship between osteoarthritis and bladder cancer: A Mendelian randomization study

OBJECTIVE

The causal association between osteoarthritis (OA) and bladder cancer remains unclear. This Mendelian randomization (MR) study was carried out to assess the potential causal effects of any OA, knee OA and hip OA, and bladder cancer.

METHOD

Genome-wide association study (GWAS) summary data for OA and bladder cancer were obtained in GWAS CATALOG, UK Biobank, and FinnGen Consortium. Inverse-variance weighted (IVW) approach was primarily conducted to evaluate the causal relationships between OA and bladder cancer, and MR-Egger intercept and Cochran's Q test were mainly used to estimate heterogeneity and pleiotropy. MR-PRESSO was used to test the presence of horizontal outliers. Leave-one-out analysis was utilized to ensure the reliability of the results.

RESULTS

A higher genetic predisposition to any OA has a causal association with bladder cancer risk, while neither knee OA nor hip OA is causally linked to bladder cancer. MR-Egger intercept analysis exhibited that any OA and knee OA had no pleiotropic effect on the risk of bladder cancer, and Cochran's Q test showed that any OA, knee OA and hip OA had no heterogeneity on bladder cancer risk. Neither MR PRESSO analysis nor leave-one-out analysis revealed any outlier SNPs.

CONCLUSIONS

This MR study exhibited a positive cause-and-effect relationship between any type of OA and bladder cancer risk, but not between site-specific OA, knee OA and hip OA, and bladder cancer. Attention should be paid to the screening and prevention of bladder cancer in OA patients at any site.

Leisure time television watching, computer use and risks of breast, colorectal and prostate cancer: A Mendelian randomisation analysis

BACKGROUND

Sedentary behaviours have been associated with increased risks of some common cancers in epidemiological studies; however, it is unclear if these associations are causal.

METHODS

We used univariable and multivariable two-sample Mendelian randomisation (MR) to examine potential causal relationships between sedentary behaviours and risks of breast, colorectal and prostate cancer. Genetic variants associated with self-reported leisure television watching and computer use were identified from a recent genome-wide association study (GWAS). Data related to cancer risk were obtained from cancer GWAS consortia. A series of sensitivity analyses were applied to examine the robustness of the results to the presence of confounding.

RESULTS

A 1-standard deviation (SD: 1.5 h/day) increment in hours of television watching increased risk of breast cancer (OR per 1-SD: 1.15, 95% confidence interval [CI]: 1.05-1.26) and colorectal cancer (OR per 1-SD: 1.32, 95% CI: 1.16-1.49) while there was little evidence of an association for prostate cancer risk (OR per 1-SD: 0.94, 95% CI: 0.84-1.06). After adjusting for years of education, the effect estimates for television watching were attenuated (breast cancer, OR per 1-SD: 1.08, 95% CI: 0.92-1.27; colorectal cancer, OR per 1-SD: 1.08, 95% CI: 0.90-1.31). Post hoc analyses showed that years of education might have a possible confounding and mediating role in the association between television watching with breast and colorectal cancer. Consistent results were observed for each cancer site according to sex (colorectal cancer), anatomical subsites and cancer subtypes. There was little evidence of associations between genetically predicted computer use and cancer risk.

CONCLUSIONS

Our univariable analysis identified some positive associations between hours of television watching and risks of breast and colorectal cancer. However, further adjustment for additional lifestyle factors especially years of education attenuated these results. Future studies using objective measures of exposure can provide new insights into the possible role of sedentary behaviour in cancer development.

Socioeconomic status, obesity, individual behaviors, diabetes, and risk for frozen shoulder: A Mendelian randomization study

There are few studies on risk factors for frozen shoulder, and even fewer Mendelian randomization (MR) studies on frozen shoulder. Therefore, we conducted a two-sample MR study to explore whether socioeconomic status (years of schooling, average total household income before tax), obesity (body mass index and waist circumference), individual behaviors (smoking initiation, alcohol intake frequency, coffee intake, nonoily fish intake, tea intake, beef intake, bread intake, cheese intake, oily fish intake, and fresh fruit intake), and diabetes (type 1 and type 2 diabetes) are associated with frozen shoulder. The exposure datasets and the outcome dataset were extracted from the MRC Integrative Epidemiology Unit at the University of Bristol Open genome-wide association studies project (https://gwas.mrcieu.ac.uk/). We conducted MR analyses using the inverse variance weighted (primary method), MR-Egger, and weighted median methods and conducted heterogeneity and pleiotropy analyses. Type 1 diabetes (OR: 1.103; 95% CI: 1.053-1.156; P = .0000410) was associated with an increased risk of frozen shoulder. Cheese intake (OR: 0.490; 95% CI: 0.267-0.899; P = .0213), non-oily fish intake (OR: 0.0993; 95% CI: 0.0220-0.448; P = .00267), years of schooling (OR: 0.453; 95% CI: 0.349-0.588; P = .00000000277), and average total household income before tax (OR: 0.434; 95% CI: 0.253-0.743; P = .00236) were discovered as protective factors. No horizontal pleiotropy was found in all analyzes we performed (P > .05). Our study indicated that type 1 diabetes was a risk factor for frozen shoulder while cheese intake, non-oily fish intake, years of schooling, and average total household income before tax were considered as protective factors for frozen shoulder.

The association between constipation and stroke based on the NHANES and Mendelian randomization study

Background

This study aimed to investigate putative causal effects between constipation and stroke using bidirectional Mendelian randomization (MR) analysis.

Methods

Based on the cross-sectional study, logistic regression models were developed to assess the association between constipation and stroke prevalence. Subsequently, genome-wide association studies statistics were employed to perform MR analysis between constipation and stroke, as well as its subtypes. The inverse variance weighting (IVW) method was the primary method, complemented by four additional methods, namely weighted median, weighted mode, simple mode, and MR-Egger regression. Cochran's Q test, MR-Egger intercept test, MR Pleiotropy RESidual Sum and Outlier, and MR Steiger test were performed to assess heterogeneity and pleiotropy effects.

Results

Constipation was associated with a greater risk of stroke even after adjusting for all covariates in logistic regression [odds ratio (OR) = 1.46, 95% confidence interval (CI) = 1.01-2.09, p = 0.042]. IVW MR analysis revealed that constipation affected large artery atherosclerosis (LAS; IVW OR = 1.5, 95% CI = 1.07-2.104, p = 0.019). No significant or suggestive association was observed with the risk of stroke or its various subtypes in MR analysis. Meanwhile, reverse MR analysis revealed no significant causal relationship between stroke or other stroke subtypes and constipation. The results of sensitivity analyses revealed no significant horizontal pleiotropy affecting causal estimates.

Conclusion

While cross-sectional studies have established that constipation increases the risk of stroke, this two-sample bidirectional MR analysis revealed a positive correlation between constipation and LAS. However, no such correlation was observed between constipation and stroke, including its various subtypes.

Causal associations between female reproductive behaviors and psychiatric disorders: a lifecourse Mendelian randomization study

BACKGROUND

The timings of reproductive life events have been examined to be associated with various psychiatric disorders. However, studies have not considered the causal pathways from reproductive behaviors to different psychiatric disorders. This study aimed to investigate the nature of the relationships between five reproductive behaviors and twelve psychiatric disorders.

METHODS

Firstly, we calculated genetic correlations between reproductive factors and psychiatric disorders. Then two-sample Mendelian randomization (MR) was conducted to estimate the causal associations among five reproductive behaviors, and these reproductive behaviors on twelve psychiatric disorders, using genome-wide association study (GWAS) summary data from genetic consortia. Multivariable MR was then applied to evaluate the direct effect of reproductive behaviors on these psychiatric disorders whilst accounting for other reproductive factors at different life periods.

RESULTS

Univariable MR analyses provide evidence that age at menarche, age at first sexual intercourse and age at first birth have effects on one (depression), seven (anxiety disorder, ADHD, bipolar disorder, bipolar disorder II, depression, PTSD and schizophrenia) and three psychiatric disorders (ADHD, depression and PTSD) (based on p<7.14×10-4), respectively. However, after performing multivariable MR, only age at first sexual intercourse has direct effects on five psychiatric disorders (Depression, Attention deficit or hyperactivity disorder, Bipolar disorder, Posttraumatic stress disorder and schizophrenia) when accounting for other reproductive behaviors with significant effects in univariable analyses.

CONCLUSION

Our findings suggest that reproductive behaviors predominantly exert their detrimental effects on psychiatric disorders and age at first sexual intercourse has direct effects on psychiatric disorders.

Causal relationship between spondylarthritis and stroke in a European population: a two sample Mendelian randomization study

Background

Observational studies have found an increased risk of stroke in patients with spondyloarthritis, but the results are susceptible to reverse causality and confounders. Therefore, the study aimed to further explore the association between spondyloarthritis and different subtypes of stroke by using a two sample Mendelian randomization (MR) analysis.

Methods

Genetic instrumental variables for spondyloarthritis were identified using summary level data from a genome-wide association study involving 201,581 people. Summary statistics from the Multiancestry Genome-wide Association Study of Stroke Consortium were used to obtain genetic data on stroke. There was no sample overlap between the exposure and outcome datasets. Inverse-variance weighted was considered the primary MR method for causal analysis. Heterogeneity, pleiotropy and sensitivity analyses were performed to ensure robustness, and single nucleotide polymorphism (SNP) with potential confounders was further screened in the PhenoScanner database to better evaluate the stability of our study.

Results

One SNP (rs1065045) was excluded due to schizophrenia. After excluding SNP (rs1065045), results of the second MR analysis were slightly different from the first, which were considered as the final result: a significant positive causality between spondyloarthritis and cardioembolic stroke (OR=1.296, 95% CI:1.094-1.534, p=0.003); a possible positive causality between spondyloarthritis and any stroke (OR=1.082, 95% CI:1.016-1.152, p=0.013)/any ischemic stroke (OR=1.086, 95% CI:1.013-1.163, p=0.020); no significant/possible causality between spondyloarthritis and small vessel stroke (OR=1.168, 95% CI:0.993-1.375, p=0.061). Insufficient power may be one possible reason why a causality was not observed between spondyloarthritis in our study.

Conclusions

This study suggests that the possible causative effects of spondyloarthritis predicted by genetics on stroke may be limited to any stroke, any ischemic stroke, and cardioembolic stroke, especially the last.

Plasma proteins and onset of type 2 diabetes and diabetic complications: Proteome-wide Mendelian randomization and colocalization analyses

We conduct proteome-wide Mendelian randomization and colocalization analyses to decipher the associations of blood proteins with the risk of type 2 diabetes and diabetic complications. Genetic data on plasma proteome are obtained from 54,306 UK Biobank participants and 35,559 Icelanders. Summary-level data on type 2 diabetes are obtained from the DIAGRAM (DIAbetes Genetics Replication And Meta-analysis consortium) consortium (74,124 cases) and FinnGen study (33,043 cases). Data on 10 diabetic complications are obtained from FinnGen and corresponding studies. Among 1,886 proteins, genetically predicted levels of 47 plasma proteins are associated with type 2 diabetes. Eleven of these proteins have strong support of colocalization. Seventeen proteins are associated with at least one diabetic complication, although a few have colocalization support. HLA-DRA, AGER, HSPA1A, and HSPA1B are associated with most microvascular complications. This study reveals causal proteins for the onset of type 2 diabetes and diabetic complications, which enhances the understanding of molecular etiology and development of therapeutics.

Causal relationship between cannabis use and cancer: a genetically informed perspective

PURPOSE

Cannabis use is increasing legally worldwide, while its impact on cancer risk is unclear. This study was performed to investigate the relationship between cannabis use and the risk of several types of cancer.

METHODS

We conducted a two-sample Mendelian randomization (MR) study to explore the causality of cannabis use on 9 site-specific types of cancer including breast cancer, cervical cancer, melanoma, colorectal cancer, laryngeal cancer, oral cancer, oropharyngeal cancer, esophageal cancer, and glioma. Genome-wide significant genetic instruments (P < 5E-06) for cannabis use were extracted from a large-scale genome-wide association meta-analysis of European ancestry, whereas cancer genetic instruments were extracted from the UK Biobank (UKB) cohort and GliomaScan consortium in the OpenGWAS database. The inverse-variance weighted (IVW) was considered the main method for MR analysis, and sensitivity analyses including MR-Egger, weighted median, MR pleiotropy residual sum, and outlier test (MR-PRESSO) were conducted to evaluate the robustness of the results.

RESULTS

Cannabis use was a significant promoting factor for cervical cancer (OR = 1.001265, 95% CI 1.000375-1.002155, P = 0.0053). And we also detected suggestive evidence of the causality of cannabis use on laryngeal cancer (OR = 1.000350, 95% CI 1.000027-1.000672, P = 0.0336) and breast cancer (OR = 1.003741, 95% CI 1.000052-1.007442, P = 0.0467). No evidence of a causal association of cannabis use with other site-specific types of cancer was detected. Additionally, no pleiotropy or heterogeneity was found in the sensitivity analysis.

CONCLUSION

This study indicates a causative association of cannabis use on cervical cancer, while cannabis use may increase the odds of breast cancer and laryngeal cancer, which require further evaluation in large-scale population-based studies.

Complexities of cerebral small vessel disease, blood pressure, and dementia relationship: new insights from genetics

Importance

There is increasing recognition that vascular disease, which can be treated, is a key contributor to dementia risk. However, the contribution of specific markers of vascular disease is unclear and, as a consequence, optimal prevention strategies remain unclear.

Objective

To disentangle the causal relation of several key vascular traits to dementia risk: (i) white matter hyperintensity (WMH) burden, a highly prevalent imaging marker of covert cerebral small vessel disease (cSVD); (ii) clinical stroke; and (iii) blood pressure (BP), the leading risk factor for cSVD and stroke, for which efficient therapies exist. To account for potential epidemiological biases inherent to late-onset conditions like dementia.

Design Setting and Participants

This study first explored the association of genetically determined WMH, BP levels and stroke risk with AD using summary-level data from large genome-wide association studies (GWASs) in a two-sample Mendelian randomization (MR) framework. Second, leveraging individual-level data from large longitudinal population-based cohorts and biobanks with prospective dementia surveillance, the association of weighted genetic risk scores (wGRSs) for WMH, BP, and stroke with incident all-cause-dementia was explored using Cox-proportional hazard and multi-state models. The data analysis was performed from July 26, 2020, through July 24, 2022.

Exposures

Genetically determined levels of WMH volume and BP (systolic, diastolic and pulse blood pressures) and genetic liability to stroke.

Main outcomes and measures

The summary-level MR analyses focused on the outcomes from GWAS of clinically diagnosed AD (n-cases=21,982) and GWAS additionally including self-reported parental history of dementia as a proxy for AD diagnosis (ADmeta, n-cases=53,042). For the longitudinal analyses, individual-level data of 157,698 participants with 10,699 incident all-cause-dementia were studied, exploring AD, vascular or mixed dementia in secondary analyses.

Results

In the two-sample MR analyses, WMH showed strong evidence for a causal association with increased risk of ADmeta (OR, 1.16; 95%CI:1.05-1.28; P=.003) and AD (OR, 1.28; 95%CI:1.07-1.53; P=.008), after accounting for genetically determined pulse pressure for the latter. Genetically predicted BP traits showed evidence for a protective association with both clinically defined AD and ADmeta, with evidence for confounding by shared genetic instruments. In longitudinal analyses the wGRSs for WMH, but not BP or stroke, showed suggestive association with incident all-cause-dementia (HR, 1.02; 95%CI:1.00-1.04; P=.06). BP and stroke wGRSs were strongly associated with mortality but there was no evidence for selective survival bias during follow-up. In secondary analyses, polygenic scores with more liberal instrument definition showed association of both WMH and stroke with all-cause-dementia, AD, and vascular or mixed dementia; associations of stroke, but not WMH, with dementia outcomes were markedly attenuated after adjusting for interim stroke.

Conclusion

These findings provide converging evidence that WMH is a leading vascular contributor to dementia risk, which may better capture the brain damage caused by BP (and other etiologies) than BP itself and should be targeted in priority for dementia prevention in the population.

Guidelines for performing Mendelian randomization investigations: update for summer 2023

This paper provides guidelines for performing Mendelian randomization investigations. It is aimed at practitioners seeking to undertake analyses and write up their findings, and at journal editors and reviewers seeking to assess Mendelian randomization manuscripts. The guidelines are divided into ten sections: motivation and scope, data sources, choice of genetic variants, variant harmonization, primary analysis, supplementary and sensitivity analyses (one section on robust statistical methods and one on other approaches), extensions and additional analyses, data presentation, and interpretation. These guidelines will be updated based on feedback from the community and advances in the field. Updates will be made periodically as needed, and at least every 24 months.

C-Reactive Protein Levels and Risk of Cardiovascular Diseases: A Two-Sample Bidirectional Mendelian Randomization Study

Elevated C-reactive protein (CRP) levels are an indicator of inflammation, a major risk factor for cardiovascular disease (CVD). However, this potential association in observational studies remains inconclusive. We performed a two-sample bidirectional Mendelian randomization (MR) study using publicly available GWAS summary statistics to evaluate the relationship between CRP and CVD. Instrumental variables (IVs) were carefully selected, and multiple approaches were used to make robust conclusions. Horizontal pleiotropy and heterogeneity were evaluated using the MR-Egger intercept and Cochran's Q-test. The strength of the IVs was determined using F-statistics. The causal effect of CRP on the risk of hypertensive heart disease (HHD) was statistically significant, but we did not observe a significant causal relationship between CRP and the risk of myocardial infarction, coronary artery disease, heart failure, or atherosclerosis. Our primary analyses, after performing outlier correction using MR-PRESSO and the Multivariable MR method, revealed that IVs that increased CRP levels also increased the HHD risk. However, after excluding outlier IVs identified using PhenoScanner, the initial MR results were altered, but the sensitivity analyses remained congruent with the results from the primary analyses. We found no evidence of reverse causation between CVD and CRP. Our findings warrant updated MR studies to confirm the role of CRP as a clinical biomarker for HHD.

Body Fat Distribution, Fasting Insulin Levels, and Insulin Secretion: A Bidirectional Mendelian Randomization Study

CONTEXT

Hyperinsulinemia and adiposity are associated with one another, but the directionality of this relation is debated.

OBJECTIVE

Here, we tested the direction of the causal effects of fasting insulin (FI) levels and body fat accumulation/distribution using 2-sample bidirectional Mendelian randomization (MR).

METHODS

We included summary statistics from large-scale genome-wide association studies for body mass index (BMI, n = 806 834), waist to hip ratio adjusted for BMI (WHRadjBMI, n = 694 649), abdominal subcutaneous, visceral and gluteofemoral adipose tissue (n = 38 965), FI levels (n = 98 210), pancreatic islets gene expression (n = 420), and hypothalamus gene expression (n = 155). We used inverse variance-weighted and robust MR methods that relied on statistically and biologically driven genetic instruments.

RESULTS

Both BMI and WHRadjBMI were positively associated with FI. Results were consistent across all robust MR methods and when variants mapped to the hypothalamus (presumably associated with food behavior) were included. In multivariable MR analyses, when waist circumference and BMI were mutually adjusted, the direct effect of waist circumference on FI was 2.43 times larger than the effect of BMI on FI. FI was not associated with adiposity. By contrast, using genetic instruments mapped to gene expression in pancreatic islets (presumably more specific to insulin secretion), insulin was positively associated with BMI and abdominal subcutaneous and gluteofemoral adipose tissue, but not with visceral adipose tissue.

CONCLUSION

Although these results will need to be supported by experimental investigations, results of this MR study suggest that abdominal adiposity may be a key determinant of circulating insulin levels. Alternatively, insulin secretion may promote peripheral adipose tissue accumulation.

Using allele scores to identify confounding by reverse causation: studies of alcohol consumption as an exemplar

BACKGROUND

Mendelian randomization (MR) is a form of instrumental variable analysis used to investigate causality using observational data. Another important, although less frequently applied, use of this technique is to investigate confounding due to reverse causality.

METHODS

We used a form of reverse MR and data from UK Biobank in a proof-of-principle study to investigate confounding due to reverse causation. Here we focus on the association between alcohol consumption (exposure) and outcomes including educational attainment, and physical and mental health. First, we examined the observational relationship between alcohol consumption and these outcomes. Allele scores were then derived for educational attainment, and physical and mental health, and the association with alcohol consumption (as the outcome) was explored. Sample sizes ranged from 114 941-336 473 in observational analyses and 142 093-336 818 in genetic analyses.

RESULTS

Conventional observational analyses indicated associations between alcohol consumption and a number of outcomes (e.g. neuroticism, body mass index, educational attainment). Analyses using allele scores suggested evidence of reverse causation for several of these relationships (in particular physical health and educational attainment).

CONCLUSION

Allele scores allow us to investigate reverse causation in observational studies. Our findings suggest that observed associations implying beneficial effects of alcohol consumption may be due to confounding by reverse causation in many cases.

Comparison of intergenerational instrumental variable analyses of body mass index and mortality in UK Biobank

BACKGROUND

An increasing proportion of people have a body mass index (BMI) classified as overweight or obese and published studies disagree whether this will be beneficial or detrimental to health. We applied and evaluated two intergenerational instrumental variable methods to estimate the average causal effect of BMI on mortality in a cohort with many deaths: the parents of UK Biobank participants.

METHODS

In Cox regression models, parental BMI was instrumented by offspring BMI using an 'offspring as instrument' (OAI) estimation and by offspring BMI-related genetic variants in a 'proxy-genotype Mendelian randomization' (PGMR) estimation.

RESULTS

Complete-case analyses were performed in parents of 233 361 UK Biobank participants with full phenotypic, genotypic and covariate data. The PGMR method suggested that higher BMI increased mortality with hazard ratios per kg/m2 of 1.02 (95% CI: 1.01, 1.04) for mothers and 1.04 (95% CI: 1.02, 1.05) for fathers. The OAI method gave considerably higher estimates, which varied according to the parent-offspring pairing between 1.08 (95% CI: 1.06, 1.10; mother-son) and 1.23 (95% CI: 1.16, 1.29; father-daughter).

CONCLUSION

Both methods supported a causal role of higher BMI increasing mortality, although caution is required regarding the immediate causal interpretation of these exact values. Evidence of instrument invalidity from measured covariates was limited for the OAI method and minimal for the PGMR method. The methods are complementary for interrogating the average putative causal effects because the biases are expected to differ between them.

Ovarian Cancer and Parkinson's Disease: A Bidirectional Mendelian Randomization Study

(1) Background: Ovarian cancer (OC) and Parkinson's disease (PD) represent a huge public health burden. The relationship of these two diseases is suggested in the literature while not fully understood. To better understand this relationship, we conducted a bidirectional Mendelian ran-domization analysis using genetic markers as a proxy. (2) Methods: Utilizing single nucleotide polymorphisms associated with PD risk, we assessed the association between genetically predicted PD and OC risk, overall and by histotypes, using summary statistics from previously conducted genome-wide association studies of OC within the Ovarian Cancer Association Consortium. Similarly, we assessed the association between genetically predicted OC and PD risk. The inverse variance weighted method was used as the main method to estimate odds ratios (OR) and 95% confidence intervals (CI) for the associations of interest. (3) Results: There was no significant association between genetically predicted PD and OC risk: OR = 0.95 (95% CI: 0.88-1.03), or between genetically predicted OC and PD risk: OR = 0.80 (95% CI: 0.61-1.06). On the other hand, when examined by histotypes, a suggestive inverse association was observed between genetically predicted high grade serous OC and PD risk: OR = 0.91 (95% CI: 0.84-0.99). (4) Conclusions: Overall, our study did not observe a strong genetic association between PD and OC, but the observed potential association between high grade serous OC and reduced PD risk warrants further investigation.

Allometric body shape indices, type 2 diabetes and kidney function: A two-sample Mendelian randomization study

AIM

To examine the association between body mass index (BMI)-independent allometric body shape indices and kidney function.

MATERIALS AND METHODS

We performed a two-sample Mendelian randomization (MR) analysis, using summary statistics from UK Biobank, CKDGen and DIAGRAM. BMI-independent allometric body shape indices were: A Body Shape Index (ABSI), Waist-Hip Index (WHI) and Hip Index (HI). Kidney function outcomes were: urinary albumin-to-creatinine ratio (UACR), estimated glomerular filtration rate and blood urea nitrogen. Furthermore, we investigated type 2 diabetes (T2D) as a potential mediator on the pathway to albuminuria. The main analysis was inverse variance-weighted random-effects MR in participants of European ancestry. We also performed several sensitivity MR analyses.

RESULTS

A 1-standard deviation (SD) increase in genetically predicted ABSI and WHI levels was associated with higher UACR (β = 0.039 [95% confidence interval: 0.016, 0.063] log [UACR], P = 0.001 for ABSI, and β = 0.028 [0.012, 0.044] log [UACR], P = 6 x 10^-4 for WHI) in women, but not in men. Meanwhile, a 1-SD increase in genetically predicted HI was associated with lower UACR in women (β = -0.021 [-0.041, 0.000] log [UACR], P = 0.05) and in men (β = -0.026 [-0.058, 0.005] log [UACR], P = 0.10). Corresponding estimates in individuals with diabetes were substantially augmented. Risk of T2D increased for genetically high ABSI and WHI in women (P < 6 x 10^-19 ) only, but decreased for genetically high HI in both sexes (P < 9 x 10^-3 ). No other associations were observed.

CONCLUSIONS

Genetically high HI was associated with decreased risk of albuminuria, mediated through decreased T2D risk in both sexes. Opposite associations applied to genetically high ABSI and WHI in women only.

Associations Between Mean Platelet Volume and Risk of Deep Vein Thrombosis: A Mendelian Randomization Study and a Retrospective Study

Objective

In this study, it was intended to explore the causal association between mean platelet volume (MPV) and risk of deep vein thrombosis (DVT) using a two-sample Mendelian randomization (MR) analysis and a retrospective study.

Methods

This study applied two-sample MR analysis to estimate the causal association between MPV and risk of DVT. Twenty-one single nucleotide polymorphisms (SNPs) were selected as genetic variants from two independent consortiums cohorts (p-value <5×10^-8, linkage disequilibrium r²<0.1). Inverse variance weighted (IVW), MR-egger method and weighted median were performed. A retrospective study was also conducted to verify the associations identified from the MR study.

Results

The MR analysis demonstrated that genetically predicted higher MPV was associated with significantly lower risk of DVT (OR 0.982, 95% CI = 0.967-0.998, P = 0.023), with the consistent result in weighted median and MR-Egger. There was no directional horizontal pleiotropy in the method of MR-Egger regression (intercept=2.9e-04, P = 0.194). There was no single SNP was found to strongly drive the combined causal effect in the leave-one-out sensitivity analysis. Additionally, the similar result was observed in the retrospective study.

Conclusion

This study suggested that MPV was negatively associated with the risk of DVT. More basic researches are needed in the future to explore its specific mechanism.

Using genetic association data to guide drug discovery and development: Review of methods and applications

Evidence on the validity of drug targets from randomized trials is reliable but typically expensive and slow to obtain. In contrast, evidence from conventional observational epidemiological studies is less reliable because of the potential for bias from confounding and reverse causation. Mendelian randomization is a quasi-experimental approach analogous to a randomized trial that exploits naturally occurring randomization in the transmission of genetic variants. In Mendelian randomization, genetic variants that can be regarded as proxies for an intervention on the proposed drug target are leveraged as instrumental variables to investigate potential effects on biomarkers and disease outcomes in large-scale observational datasets. This approach can be implemented rapidly for a range of drug targets to provide evidence on their effects and thus inform on their priority for further investigation. In this review, we present statistical methods and their applications to showcase the diverse opportunities for applying Mendelian randomization in guiding clinical development efforts, thus enabling interventions to target the right mechanism in the right population group at the right time. These methods can inform investigators on the mechanisms underlying drug effects, their related biomarkers, implications for the timing of interventions, and the population subgroups that stand to gain the most benefit. Most methods can be implemented with publicly available data on summarized genetic associations with traits and diseases, meaning that the only major limitations to their usage are the availability of appropriately powered studies for the exposure and outcome and the existence of a suitable genetic proxy for the proposed intervention.

Can Intelligence Affect Alcohol-, Smoking-, and Physical Activity-Related Behaviors? A Mendelian Randomization Study

People with high levels of intelligence are more aware of risk factors, therefore choosing a healthier lifestyle. This assumption seems reasonable, but is it true? Previous studies appear to agree and disagree. To cope with the uncertainty, we designed a mendelian randomization (MR) study to examine the causal effects of genetically proxied intelligence on alcohol-, smoking-, and physical activity (PA)-related behaviors. We obtained genome-wide association study (GWAS) datasets concerning these variables from separate studies or biobanks and used inverse-variance weighted (IVW) or MR-Egger estimator to evaluate the causal effects according to an MR protocol. The MR-Egger intercept test, MR-PRESSO, and funnel plots were employed for horizontal pleiotropy diagnosis. The Steiger test (with reliability test), Cochran's Q test, MR-PRESSO, and leave-one-out method were employed for sensitivity analysis. We found significant or potential effects of intelligence on alcohol dependence (OR = 0.749, p = 0.003), mental and behavioral disorders due to alcohol (OR = 0.814, p = 0.009), smoking (OR = 0.585, p = 0.005), and smoking cessation (OR = 1.334, p = 0.001). Meanwhile, we found significant or potential effects on walking duration (B = -0.066, p < 0.001), walking frequency (B = -0.055, p = 0.031), moderate PA frequency (B = -0.131, p < 0.001), and vigorous PA frequency (B = -0.070, p = 0.001), but all in a negative direction. In conclusion, our findings reinforce some existing knowledge, indicate the complexity of the health impacts of human intelligence, and underline the value of smoking and alcohol prevention in less intelligent populations. Given the existing limitations in this study, particularly the potential reverse causality in some estimations, re-examinations are warranted in future research.

Genetic proxies for PCSK9 inhibition associate with lipoprotein(a): Effects on coronary artery disease and ischemic stroke

BACKGROUND AND AIMS

Post hoc analyses of clinical trials show that PCSK9 inhibitors might lower lipoprotein(a), but whether this effect contributes to reductions in cardiovascular risk remains unknown. We aimed to assess whether genetically proxied PCSK9 inhibition influences lipoprotein(a) (Lp(a)), and whether any such effect could mediate its effects on coronary artery disease (CAD) and ischemic stroke (IS).

METHODS

To explore associations between the genetic proxies for PCSK9 inhibitors and Lp(a) levels, we used UK Biobank data (310,020 individuals). We identified 10 variants in the PCSK9 gene associated with lower PCSK9 and LDL-C levels as proxies for PCSK9 inhibition. We explored the effects of genetically proxied PCSK9 inhibition on Lp(a) levels, as well as on odds of CAD (60,801 cases, 184,305 controls) and IS (60,341 cases, 454,450 controls) in two-sample Mendelian randomization analyses. In mediation analyses, we assessed the effects of genetically proxied PCSK9 inhibition on CAD and IS mediated through reductions in Lp(a) levels.

RESULTS

Genetically proxied PCSK9 inhibition (1-SD decrement in PCSK9 concentration; corresponding to 20.6 mg/dl decrement in LDL-C levels) was associated with a 4% decrease in log-Lp(a) levels (beta: -0.038, 95%CI: -0.053 to -0.023). We estimated a 0.8% reduction in the odds for CAD (OR: 0.992, 95%CI: 0.989-0.995) and a 0.5% reduction in the odds for atherosclerotic IS (OR: 0.995, 95%CI: 0.992-0.998) due to reductions in Lp(a) levels through genetically proxied PCSK9 inhibition, corresponding to 3.8% and 3.2% of the total effects, respectively.

CONCLUSIONS

Genetic proxies for PCSK9 inhibition are associated with lower Lp(a) levels. However, Lp(a) lowering explains only a small proportion of the total effects of genetic proxies for PCSK9 inhibitors on risk of CAD and IS.