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PubMed2025

Immunosuppressant use may be a potential mediator in the progression of systemic lupus erythematosus to osteomyelitis: A bidirectional Mendelian randomization study.

The prevalence of osteomyelitis (OM) is elevated in patients with systemic lupus erythematosus (SLE), but the causal direction and proportion of immunosuppressant (IS) use in this relationship is unclear. Therefore, this study used a bidirectional Mendelian randomization (MR) study to investigate the causal relationship between SLE and OM and to quantify the role of IS use as a potential mediator. Genome-wide association study summary-level data were used to obtain genetic instrumental variables for SLE (5201 cases and 9066 controls), OM (1881 cases and 391,037 controls), and IS (3954 cases and 268,648 controls) genetic instrumental variables with no overlap between their participant populations. Causal and total effects of SLE and OM were analyzed using bidirectional MR. Subsequent "2-step" MR was used to assess the direct effect between the 2 and the indirect effect of IS. Inverse variance weighting was used as the primary method of MR, while a series of sensitivity analyses were performed to assess the reliability of the results. Forward MR of inverse variance weighting results demonstrated a positive causal association between SLE and OM (P = .003, odds ratio [OR] = 1.062, 95% confidence interval [Cl]-OR: 1.019-1.107). The reverse MR results indicated no causal effect of OM on SLE was found (P = .503, OR = 0.914, 95% Cl-OR: 0.703-1.188). The direct effect of SLE acting on OM in our study was found to be 19.36% by 2-step analysis, and the indirect effect of OM through IS was found to be 68.11% (proportion mediated: 68.11%; 95% CI = 0.2277331-1.134507). There was no heterogeneity in all MR analyses of causality, except for the MR analysis of SLE causally related to IS. Sensitivity analysis found no evidence of horizontal pleiotropy. The present study found an increased relative risk of OM in SLE. Mediation analysis suggested a potential substantial mediating role for IS; however, this estimate was highly imprecise and requires further validation. In clinical practice, clinicians should remain aware of the potential for IS therapy to influence infection risk, including OM, in SLE patients.

Humans↗

PubMed2026

Modelling time-varying genetic effects on binary disease risk via functional Mendelian randomization.

MOTIVATION: Genome-wide association studies have identified thousands of genetic variants associated with complex traits, establishing Mendelian randomization (MR) as a powerful framework for causal inference using variants as natural experiments. However, existing MR methods treat causal effects as static, relying on cross-sectional exposure measurements and ignoring how genetic predispositions to disease operate dynamically across the life course. Recovering age-specific causal effect functions from longitudinal data requires combining functional data representations of exposure trajectories with instrumental variable estimation strategies suitable for binary disease endpoints, a methodological gap that has remained unaddressed. RESULTS: We develop a functional MR framework for binary outcomes that integrates functional principal component analysis with two-stage residual inclusion (2SRI), ensuring consistent estimation under the nonlinear logistic link function that renders standard instrumental variable estimators inconsistent. Simulations across different causal effect trajectory shapes, varying measurement densities, and varying instrument strengths demonstrate accurate recovery of time-varying genetically predicted effects with minimal bias. Applied to UK Biobank data, the framework identifies an age-specific causal effect of genetically predicted body mass index on type 2 diabetes risk concentrated in early mid-adulthood and progressively attenuating thereafter. Concordance between the proposed 2SRI estimator applied to type 2 diabetes and the established continuous-outcome functional MR estimator applied to the paired glycated haemoglobin marker in the same cohort provides indirect empirical support for the validity of the proposed approach. AVAILABILITY AND IMPLEMENTATION: The method is implemented in the R package mvfmr, with a full tutorial vignette.

Mendelian Randomization Analysis↗

PubMed2026

Novel Insights into Immune Cell Function in Type 2 Diabetes Mediated by Gut Microbiota: A Two-Sample Mendelian Randomization Study.

INTRODUCTION: The role of immune cells in type 2 diabetes mellitus (T2DM) development is well-studied, but their interactions with the gut microbiota and the mediating role in this process remain unclear. METHODS: We analyzed 731 immune cell phenotypes (3,757 Europeans), 473 gut microbiota traits (5,959 Finns), and T2DM data (over 400,000 Finns). Mendelian randomization (MR) was based on three assumptions: the instrumental variable (IV) is associated with exposure, IV is not influenced by confounding, and IV affects the outcome only through exposure. We selected single-nucleotide polymorphisms (SNPs) from genome-wide association studies as instrumental variables (IVs) to infer causal effects in two-sample MR analysis. RESULTS: We identified 36 immune cell phenotypes associated with T2DM, including 29 protective factors and seven risk factors, as well as 10 gut microbiota significantly linked to T2DM, with eight protective factors and two risk factors. MR revealed that five gut microbiota mediated the relationship between immune cells and T2DM. For example, the effects of CD3 on resting Treg (OR: 1.0136), CD3 on CM CD4+ (OR: 1.0180), and CD3 on naive CD4+ cells (OR: 1.0150) in T2DM were found to be partially mediated by the species Bacillus. AYThe corresponding mediation effect proportions were 8.99%, 11.8%, and 11.4%. DISCUSSION: MR analysis identified multiple gut microbiota mediators in the relationship between immune cells and T2DM, addressing previous observational evidence. Limitations included the European ancestry bias, among others. CONCLUSION: This study has highlighted the gut microbiota as a mediator between immune cells and T2DM, offering new insights for its early prevention and intervention.

Diabetes Mellitus, Type 2↗

PubMed2025

Association between NAFLD and liver cancer: A two-sample Mendelian randomization study.

Observational studies suggest an association between nonalcoholic fatty liver disease (NAFLD) and liver cancer, but its causal nature remains unclear. A 2-sample Mendelian randomization (MR) analysis was performed using NAFLD and liver cancer summary statistics from genome-wide association study databases. Instrumental variables satisfying the 3 core MR assumptions were selected. Causal effects were estimated using inverse-variance weighted, MR-Egger, weighted median, and other methods, followed by sensitivity and power analyses. All 4 MR analyses demonstrated a positive causal association between NAFLD and liver cancer risk [odds ratio > 1, inverse-variance weighted P < .001]. Sensitivity analysis indicated no significant level of multiplicity or heterogeneity in the instrumental variables, and individual single nucleotide polymorphisms had no significant impact on the results. However, statistical power was insufficient. This study provides the first MR evidence demonstrating a genetically predicted causal relationship between NAFLD and liver cancer that is consistent across subtypes. Sensitivity analyses confirmed the absence of horizontal pleiotropy or heterogeneity, strengthening the robustness of the findings. These results offer genetic support for early NAFLD intervention to reduce the risk of liver cancer. However, the limited statistical power highlights the need for larger-scale genome-wide association study to identify more and stronger genetic instruments for a more precise quantification of the causal effect of NAFLD on liver cancer risk.

Humans↗

PubMed2024

Assessing the causal link between liver function and acute pancreatitis: A Mendelian randomisation study.

A correlation has been reported to exist between exposure factors (e.g. liver function) and acute pancreatitis. However, the specific causal relationship remains unclear. This study aimed to infer the causal relationship between liver function and acute pancreatitis using the Mendelian randomisation method. We employed summary data from a genome-wide association study involving individuals of European ancestry from the UK Biobank and FinnGen. Single-nucleotide polymorphisms (SCNPs), closely associated with liver function, served as instrumental variables. We used five regression models for causality assessment: MR-Egger regression, the random-effect inverse variance weighting method (IVW), the weighted median method (WME), the weighted model, and the simple model. We assessed the heterogeneity of the SNPs using Cochran's Q test. Multi-effect analysis was performed using the intercept term of the MR-Egger method and leave-one-out detection. Odds ratios (ORs) were used to evaluate the causal relationship between liver function and acute pancreatitis risk. A total of 641 SNPs were incorporated as instrumental variables. The MR-IVW method indicated a causal effect of gamma-glutamyltransferase (GGT) on acute pancreatitis (OR = 1.180, 95%CI [confidence interval]: 1.021-1.365, P = 0.025), suggesting that GGT may influence the incidence of acute pancreatitis. Conversely, the results for alkaline phosphatase (ALP) (OR = 0.997, 95%CI: 0.992-1.002, P = 0.197) and aspartate aminotransferase (AST) (OR = 0.939, 95%CI: 0.794-1.111, P = 0.464) did not show a causal effect on acute pancreatitis. Additionally, neither the intercept term nor the zero difference in the MR-Egger regression attained statistical significance (P = 0.257), and there were no observable gene effects. This study suggests that GGT levels are a potential risk factor for acute pancreatitis and may increase the associated risk. In contrast, ALP and AST levels did not affect the risk of acute pancreatitis.

Humans↗

PubMed1977

Socio-psychological factors and metabolic control in juvenile diabetes.

The influence of exogenous and environmental factors on metabolic control was studied in 58 insulin treated juvenile diabetics, 6-17 years of age. Duration of diabetes varied between 3-14 years and age at onset of diabetes between 1-13 years. The social situation as well as knowledge about and attitudes towards diabetes among the patients and their parents were estimated by interviews, questionnaires and special tests. The quality of the diet, exercise and insulin treatment was assessed. An index of diabetic control was calculated on the basis of the patients daily urinalysis made at home. Multiple regression analysis and a special statistical "instrumental" variable technique were used in an effort to analyse the correlations between all variables. The social situation of the diabetic children was comparable with that of other Swedish children, but many parents felt the economic burden of the diabetic treatment as a problem. Knowledge tests showed that 25% of the parents and 62% of the patients above 12 years had unsatisfactory knowledge about diabetes. However, 93% of the patients seemed to have predominantly positive attitudes towards the treatment. Severe psychological problems had occurred in 7 cases. Food habits were appropriate among 21% of the patients and 26% had very regular exercise customs. Physical exercise seemed to be the most important of the exogenous factors for the diabetic control (p less than 0.001). Among teenagers knowledge was positively correlated to positive attitudes which in turn were positively correlated to physical exercise. Instrumental variable technique gave further indications of a positive influence of knowledge on control, and the correlation between diabetic control on one hand and knowledge combined with positive attitudes on the other was significantly positive. The results emphasize the importance of assisting young diabetic patients and their families in their socio-psychological adaptation to the strains of diabetic therapy.

Adolescent↗

PubMed2025

Exploring the causal association between television viewing and meniscal injuries: A two-sample Mendelian randomization analysis.

The aim of this study was to assess whether there is a potential causal relationship between sedentary behavior and meniscal injuries based on the Mendelian randomization (MR) method. This study used a two-sample MR design to integrate pooled data from a large-scale genome-wide association studies (GWAS). Single nucleotide polymorphisms (SNPs) that were significantly associated with sedentary behavior (represented by daily TV-viewing time) and independent of each other were selected as instrumental variables, while focusing on data from populations of European ancestry. To ensure the robustness and reliability of the analyses, 3 mainstream MR analysis methods were combined in this study: inverse variance weighted (IVW), weighted median estimation (WME) and MR-Egger regression. Heterogeneity test, horizontal multivariate analysis, and leave-one-out sensitivity test were also conducted to further validate the stability of causal estimation. The results of the IVW method showed that sedentary behavior was significantly associated with the risk of meniscus injury, with an OR (95% CI) of 2.93 (1.89-4.52), and a P-value of < .001, suggesting that sedentary behavior may be an important risk factor for meniscus injury. No significant bias was found in the heterogeneity test and the assessment of multiple validity, and the sensitivity analysis showed that the effect of individual SNPs on the overall estimation was small, and the results had good robustness. This study provides genetic epidemiological evidence of a positive causal effect of sedentary behavior on meniscal injuries based on a causal inference approach with genetic instrumental variables. The results suggest that reducing sedentary time, especially prolonged TV watching behavior, may reduce the risk of meniscus injury to some extent.

Humans↗

PubMed1978

A variable focus telescopic instrument for indirect ophthalmoscopy with increased magnification and stereopsis.

We devised a new binocular indirect ophthalmoscope and a complimentary examination technique that provide enhanced fundus magnification and optimum stereopsis through a wide range of patient pupillary apertures. The lightweight, mechanically simple instrument uses a variable focus Galilean telescopic observation system to enlarge the condensing lens image of the fundus seen by the examiner. The present device is capable of about X 1.5 fundus magnification with negligible stereopsis through a 20-mm patient pupil, continuously increasing to X 8.5 with greatly enhanced stereopsis through an 8-mm pupil. A zoom focusing capability considerably extends the magnification, stereopsis, and small pupip penetrating characteristics of a given condensing lens by allowing the examiner to binocularly observe the telescopically magnified fundus image throughout the 30-cm to 60-cm focusing range of the ophthalmoscope.

Fundus Oculi↗

PubMed2026

Assessing the Association Between Age at First Sexual Intercourse and HIV Infection Risk Using A Two-sample Mendelian Randomization Framework.

This study applied a two-sample Mendelian randomization framework to investigate the potential association between age at first sexual intercourse (AFS) and the risk of Human Immunodeficiency Virus (HIV) infection. Summary-level Genome-Wide Association Study (GWAS) data from European populations were analyzed, including 214,547 individuals for AFS and 357 HIV cases with 218,435 controls from the FinnGen R5 dataset. Independent single-nucleotide polymorphisms significantly associated with AFS were selected as instrumental variables following linkage disequilibrium clumping and instrument-strength assessment. Causal estimates were evaluated using inverse-variance weighting (IVW), MR-Egger regression, weighted median, weighted mode, and simple mode. Cochran's Q test, MR-Egger intercept analysis, MR-PRESSO assessment, and leave-one-out sensitivity analyses were performed to evaluate heterogeneity, pleiotropy, and robustness. The IVW analysis suggested that genetically predicted later AFS was associated with reduced HIV infection risk (OR = 0.192, 95% CI = 0.062-0.592, P = 0.004), whereas earlier sexual debut corresponded to increased HIV susceptibility. Directionally consistent findings across multiple Mendelian randomization methods supported the stability of the observed association. However, the findings should be interpreted cautiously because the HIV outcome analysis relied on a single dataset with a limited number of HIV cases. These results support a potential association between earlier sexual debut and HIV susceptibility and demonstrate the utility of Mendelian randomization for investigating behavioral risk factors associated with infectious disease outcomes.

Humans↗

PubMed2026

Causal Relationship Between Ischemic Stroke and Vascular Dementia: A Mendelian Randomization Study.

Ischemic stroke (IS) is a major cause of disability and mortality worldwide, and vascular dementia (VaD) is a common dementia subtype associated with cerebrovascular injury. Observational studies have suggested a relationship between IS and VaD, but these studies are vulnerable to confounding and reverse causality. This protocol describes a reproducible two-sample Mendelian randomization (MR) workflow for evaluating the potential causal association between IS and VaD using publicly available genome-wide association study (GWAS) summary statistics. Genetic instruments associated with IS were extracted from a public GWAS dataset, and outcome associations for VaD were obtained from a public VaD GWAS dataset. The corresponding dataset IDs are provided in the Protocol section. After outcome matching and allele harmonization, 51 single-nucleotide polymorphisms (SNPs) were retained for the final MR analysis. The workflow includes instrumental variable selection, linkage disequilibrium clumping, allele harmonization, instrument strength assessment, inverse variance weighted (IVW) analysis, weighted median analysis, MR-Egger analysis, heterogeneity testing, horizontal pleiotropy assessment, and leave-one-out sensitivity analysis. In the representative analysis, the IVW method showed a positive association between genetically predicted IS and VaD risk, and the weighted median method yielded a directionally concordant result. The MR-Egger estimate was directionally consistent but did not reach statistical significance. Therefore, these findings should be interpreted as suggestive evidence of a possible causal effect, rather than definitive proof of causality. This protocol may help researchers apply a transparent and reproducible MR workflow to investigate cerebrovascular disease-related outcomes using public GWAS data.

Humans↗

PubMed2025

No More Free Lunch: Challenges to Mendelian Randomization Due to Sample Selection and Complex Methods.

Mendelian randomization (MR) is increasingly used in epidemiological studies to investigate causal relationships. MR depends on 3 fundamental instrumental variable assumptions: relevance, independence, and exclusion restriction. Studies often assume that MR mitigates bias from confounding due to the random allocation of genetic variants at conception. In this perspective, using causal directed acyclic graphs, we discuss several scenarios where biases in MR analyses may arise due to the nature of the data or methods being used. These include (1) collider bias due to the nonrandom selection of participants into study populations used for conducting genome-wide association studies (GWAS), (2) indirect genetic effects arising from population-based GWAS rather than within-family studies, and (3) collider bias due to gene-environment interaction effects on the exposure in nonlinear MR analyses. We provide practical considerations for examining and reducing these biases in MR analyses.

Humans↗

PubMed2026

The Association of Allergic Rhinitis with Chronic Adenotonsillar Diseases and Chronic Rhinosinusitis: A Mendelian Randomization Study.

INTRODUCTION: Allergic rhinitis (AR) has long been considered to be associated with chronic adenotonsillar disease (CATD). However, their causal relationship remains unclear. This study aims to investigate the causal relationship between AR and CATD and to examine the mediating role of chronic rhinosinusitis (CRS) in this association. METHODS: This study employed a two-sample Mendelian randomization (MR) design using genetic instrumental variable analysis. Data for allergic rhinitis (AR) were obtained from the MRC IEU OpenGWAS data infrastructure, data for chronic adenotonsillar disease (CATD) from the FinnGen biobank, and data for chronic rhinosinusitis (CRS) from the GWAS Catalog. Several MR methods were applied. In addition, a two-step MR approach was used to investigate the mediating role of CRS in the relationship between AR and CATD. RESULTS: MR analysis identified a positive correlation between AR and CATD. IVW and weighted median analyses showed significant causal effects (beta = 0.55, 95% CI: 0.26 to 0.84); p <0.001). No causal association was found between CATD and AR. AR and CRS showed a positive correlation (beta = 1.38, 95% CI: 0.78 to 1.98; p = 6.5 × 10-6). CRS had a beta value of 0.15 (95% CI: 0.06 to 0.24; p = 0.001) for CATD. CRS mediates 37.6% of the AR to CATD pathway (mediation effect = 0.20, 95% CI: 0.04 to 0.37; p = 0.013). DISCUSSION: These findings indicate that AR may contribute to CATD risk through CRS, highlighting the need for further research to explore underlying biological mechanisms and validate these findings. CONCLUSIONS: This study suggests a positive causal relationship between AR and CATD, with CRS acting as a mediator.

Mendelian Randomization Analysis↗

PubMed2026

Causal relationship between asthma and hernia risk: A Mendelian randomization study.

Epidemiological associations between asthma and various hernia subtypes have been reported, but the causality and direction remain unclear. This study employs a two‑sample Mendelian randomization (MR) approach to systematically assess the causal associations between asthma and 6 hernia subtypes. Using publicly available summary data of genome-wide association studies, asthma was selected as the exposure, and diaphragmatic hernia, umbilical hernia, femoral hernia, hiatus hernia, inguinal hernia, and ventral hernia were selected as outcomes. Instrumental variables were strictly screened (F-statistic > 10). The inverse‑variance weighted method was used as the primary analytical approach, supplemented with MR Egger and weighted median methods. Sensitivity analyses included heterogeneity tests, horizontal pleiotropy tests, Steiger directionality tests, leave‑one‑out analyses, and Radial MR. Reverse MR was performed for validation. Forward MR analyses revealed a significant positive causal effect of asthma on diaphragmatic hernia (odds ratio [OR] = 1.19, 95% confidence interval [CI]: 1.08-1.31, P < .001) and a suggestive association with umbilical hernia (OR = 1.19, 95% CI: 1.05-1.34, P = .007). The umbilical hernia association was significant only by the inverse‑variance weighted method; weighted median (P = .102) and MR-Egger (P = .210) estimates were not statistically significant, and the estimate attenuated after outlier removal (confirmatory OR = 1.13, 95% CI: 1.01-1.26, P = .028). Sensitivity analyses showed no significant heterogeneity or pleiotropy. Reverse MR did not identify significant causal effects of hernias on asthma, although power limitations for certain hernia subtypes should be considered. No significant associations were observed between asthma and the other hernia subtypes, although the null findings for femoral and ventral hernias should be interpreted with caution due to limited statistical power. This study provides genetic evidence supporting asthma as a causal risk factor for diaphragmatic hernia, with a suggestive association for umbilical hernia. The diaphragmatic hernia finding was robust across multiple sensitivity analyses, whereas the umbilical hernia association was less consistent and requires further confirmation. These findings contribute to a deeper understanding of the mechanistic links between asthma and specific hernia subtypes.

Mendelian Randomization Analysis↗

PubMed2026

NLCD: A method to discover nonlinear causal relations among genes.

Distinguishing correlation from causation is a fundamental challenge in many scientific fields, including biology, especially when interventions like randomized controlled trials are infeasible and only observational data are available. Methods based on statistical tests of conditional independence within the Mendelian Randomization framework can detect causality between two observed variables that are each associated with a third instrumental variable. However, these methods for detecting causal relationships between traits (e.g., two gene expression or clinical traits associated with a genetic variant, all observed in the same population) often assume a linear relationship, thereby hindering the discovery of causal gene networks from genomics data. We have developed NLCD, a method for NonLinear Causal Discovery from genomics data based on nonlinear regression modeling and conditional feature importance scoring. NLCD uses these techniques to extend the statistical tests in an existing linear causal discovery method called the Causal Inference Test (CIT). We benchmarked NLCD against current state-of-the-art methods: CIT, Findr, and MRPC. On simulated datasets, NLCD performs comparably to most methods in detecting linear relations (Average AUPRC (Area Under the Precision-Recall Curve) of NLCD = 0.94, CIT = 0.94, Findr = 0.94, and MRPC = 0.99), and outperforms them in detecting nonlinear (sine and sawtooth type) relations between two genes (Average AUPRC of NLCD = 0.76, CIT = 0.60, Findr = 0.56, and MRPC = 0.73). When tested on a nonlinear subset of a yeast genomic dataset to recover known causal relations involving transcription factors, NLCD and CIT performed comparable to each other and slightly better than Findr and MRPC (Average AUPRC of NLCD = 0.82, CIT = 0.81, Findr = 0.71, and MRPC = 0.54). On application to a human genomic dataset, NLCD revealed active causal gene pairs (IRF1 → PSME1 and HLA-C → HLA-T) in the muscle tissue, and clarified the promises and challenges in discovering causal gene networks in tissues under in vivo human settings.

Humans↗

PubMed2025

Exploring the causal role of plasma metabolites in pediatric asthma: a Mendelian randomization study.

BACKGROUND: Pediatric asthma (PA) is the prevailing chronic respiratory ailment in childhood. A better understanding of plasma metabolites is the goal for elucidating the molecular pathological mechanisms of PA and investigating novel therapeutic approaches. METHODS: Data for PA from Genome-Wide Association Studies (GWAS) was derived from the IEU-OpenGWAS project, featuring a collection of 1400 plasma metabolites. The inverse-variance weighting (IVW) method assessed causal relationships between plasma metabolites and PA, with measures taken to mitigate horizontal pleiotropy and heterogeneity. To select instrumental variables, a genome-wide significance threshold (p < 5 × 10-8) was applied to ensure robust genetic instruments. A Bonferroni correction controlled for multiple testing, with statistical significance defined as p < 3.57 × 10-5) (0.05/1400). To further substantiate outcomes, a reverse Mendelian randomization analysis was conducted. RESULTS: Research found 91 plasma metabolites linked to PA, ten of which showed significant associations. Of note, 20:4n6 levels (IVW: OR (95% CI) = 1.062 (1.030 to 1.094) and G/C16 (IVW: OR (95% CI) = 0.886 (0.832 to 0.943) were identified as pivotal exposure factors for PA. CONCLUSIONS: This study highlights 10 plasma metabolites that may have significant associations with PA incidence, with 20:4n6 levels and G/C16 potentially serving as valuable biomarkers for the early detection and management of PA.

Humans↗

PubMed2026

Genetically predicted CXCL16 expression is associated with Parkinson's disease risk and peripheral immune cell dysregulation: a two-sample mendelian randomization study.

BACKGROUND: Parkinson's disease (PD) is a progressive neurodegenerative disorder with limited disease-modifying therapies. PANoptosis, an integrated form of programmed cell death involving apoptosis, pyroptosis, and necroptosis, has been implicated in neuroinflammation-related neurodegeneration. However, the roles of PANoptosis-related genes in PD remain unclear. METHODS: We performed two-sample Mendelian randomization (MR) using cis-eQTL instruments from the eQTLGen Consortium for 30 PANoptosis-related genes, with PD GWAS data from Nalls et al. 2019 as the outcome. Instrumental variables were selected using a hierarchical strategy, with genome-wide significant cis-eQTLs as primary instruments and a relaxed threshold applied only for genes with fewer than three independent SNPs. Sensitivity analyses included MR-Egger, weighted median, MR-PRESSO, MR-RAPS, and leave-one-out analyses. SMR/HEIDI testing and two-step MR mediation using 731 peripheral immune traits were also performed. RESULTS: Genetically predicted higher CXCL16 expression was associated with increased PD risk (OR = 1.115, 95% CI 1.060-1.173, p = 2.4 × 10-5), while higher FADD expression was associated with reduced PD risk (OR = 0.861, 95% CI 0.790-0.939, p = 7.1 × 10-4). CASP1 and IFI27 were nominally significant and considered exploratory. Sensitivity analyses were directionally consistent, although MR-Egger estimates were imprecise. SMR/HEIDI supported CXCL16. Exploratory mediation analysis identified 63/66 candidate immune mediators after FDR correction. CONCLUSION: These findings provide MR-based genetic evidence linking CXCL16 expression to PD risk, with exploratory mediation through peripheral immune phenotypes. The CXCL16-immune cell-PD axis warrants further experimental validation.

Humans↗

PubMed2026

Bayesian Mendelian randomization reveals a protective effect of later age at first sexual intercourse against erectile dysfunction.

Erectile dysfunction (ED) is a prevalent health condition with significant psychosocial impacts, yet the causal role of age at first sexual intercourse (AFS) remains unclear. This study investigated the causal effect of AFS on the risk of ED using Mendelian randomization (MR) and Bayesian methods. Five traditional 2-sample MR analyses and 5 Bayesian MR analyses were performed using genome-wide association studies summary statistics from European populations. Sensitivity analyses included MR Egger regression, MR-pleiotropy residual sum and outlier, and Cochran Q-test. In mixed-sex cohorts (Groups 1 and 2), inverse variance weighted results demonstrated significant protective effects: odds ratio (OR) = 0.626, θ = -0.469, P = 2.73 × 10-6 for Group 1 and OR = 0.617, θ = -0.483, P = 3.56 × 10-5 for Group 2. The analyses for male-specific cohorts (Groups 3-10) showed weaker but consistent effects. For Group 3, OR = 0.643, θ = -0.442, P = .010. For Group 4, some instrumental variables associated with confounders were removed. The result became statistically insignificant: OR = 0.680, θ = -0.385, P = .064. For Group 5, the instrument selection criteria were relaxed and significance was retained: OR = 0.695, θ = -0.364, P = .016. For Groups 6 to 10, Bayesian MR was used to strengthen the inferences. In particular, for Group 8, which has a strongly informed prior, a posterior mean θ = -0.358 and a 95% credible interval (-0.575, -0.136) were obtained. This study provides evidence supporting a causal protective effect of later AFS on ED risk. While traditional MR analyses in male-specific cohorts yielded suggestive results, Bayesian MR analyses, which allow for the integration of prior evidence, provided more precise estimates and strengthened the causal inference. These findings may inform future sexual health policies. Strengths include the use of male-specific cohorts and Bayesian enhancement for weak instruments. Limitations include reliance on European-ancestry data and inability to stratify ED subtypes.

Male↗

PubMed2026

Reassessing Instrument Strength in Two-Sample Mendelian Randomization Analysis.

Mendelian randomization (MR) analysis is widely used to estimate causal relationships between risk factors and outcomes of interest. Two-sample MR approaches have gained increasing attention in genetic epidemiology due to the growing availability of Genome-Wide Association Study (GWAS) summary statistics from public databases. A critical step in two-sample MR is the selection of genetic variants as instrumental variables (IVs). Although genome-wide significant variants are typically preferred, the inclusion of variants with weaker association p-values is considered, as they may potentially improve power through an increased instrument number of instruments, while they may introduce weak instrument bias and attenuate effect estimates towards the null. Our simulation results show that even modest levels of pleiotropy substantially increase the variability of causal effect estimates, while the inclusion of weak IVs does not substantially affect the direction and variability of causal effect estimates in most cases. In real data analyses, we used two released versions of FinnGen GWAS summary statistics with different sample sizes as exposure GWASs to assess the influence of weak IVs. Here, the inclusion of IVs with higher exposure-association p-values resulted in weakened estimated effect sizes, particularly when the exposure GWAS sample size was small. These findings suggest that incorporating weak IVs is reasonable when the exposure GWAS sample size is large, but it poses a risk of falsely concluding null associations when the exposure GWAS sample size is small.

Journal Article↗