Mendelian Randomization Analysis Reveals a Complex Genetic Interplay among Atopic Dermatitis, Asthma, and Gastroesophageal Reflux Disease

Mendelian Randomization Studies in Atopic Dermatitis: A Systematic Review

Prior studies have found associations between atopic dermatitis (AD) and comorbidities, including depression, obesity, asthma, and allergic rhinitis. Although observational studies often cannot establish robust causality between potential risk factors and AD, Mendelian randomization minimizes confounding when exploring causality by relying on random allelic assortment at birth. In this study, we systematically reviewed 30 Mendelian randomization studies in AD. Body mass index, gut microbial flora, the IL-18 signaling pathway, and gastroesophageal reflux disease were among the causal factors for AD, whereas AD was causal for several medical conditions, including heart failure, rheumatoid arthritis, and conjunctivitis. These insights may improve preventive counseling in AD.

Analysis of the potential molecular mechanisms of asthma and gastroesophageal reflux disease

OBJECTIVE

Asthma and gastroesophageal reflux disease (GERD) often occur simultaneously, with GERD being a comorbidity of asthma. This study aimed to explore the biological markers related to asthma and GERD by bioinformatics analysis.

METHODS

Initially, gene expression datasets for asthma and GERD were obtained from the Gene Expression Omnibus database, and subsequent differential expression analysis yielded 620 differentially expressed genes (DEGs) for asthma and 2367 DEGs for GERD. The intersection of these two gene sets yielded a total of 84 DEGs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed that these genes may be involved in steroid hormone secretion and cellular stress response. Five hub genes (PTGDR2, CPA3, FCER1A, TPSAB1, and IL1RL1) were identified by a protein-protein interaction (PPI) network analysis and topological algorithm.

RESULTS

Enrichment analysis results indicated that hub genes may be involved in hormone secretion and disease development, particularly in regulating the renin-angiotensin system and systemic arterial blood pressure. PTGDR2, CPA3, TPSAB1, and IL1RL1 were upregulated in both asthma and GERD patient groups, while FCER1A was upregulated in asthma patients but downregulated in GERD patients. Through drug prediction, 22 drugs targeting hub genes PTGDR2, FCER1A, and TPSAB1 were identified. By constructing a transcription factor (TF)-target gene network, we found that eight TFs may regulate the expression of PTGDR2, FCER1A, and IL1RL1.

CONCLUSION

Hence, Asthma and GERD were related to steroid hormone secretion and the renin-angiotensin system.

Causal analysis between gastroesophageal reflux disease and chronic rhinosinusitis

BACKGROUND

Gastroesophageal reflux disease (GERD) and chronic rhinosinusitis (CRS) have been shown to be potentially closely related, but the relationship between these conditions, particularly the possibility of a causal link, is not fully understood. This study used Mendelian randomization (MR) to assess the causal relationship between these two disorders.

METHODS

We extracted genome-wide association study data sets for GERD and CRS from publicly available gene summaries, and used MR to conduct a causal inference analysis. The main robustness test used in this study included MR-Egger regression, a leave-one-out sensitivity test, and multivariate MR (MVMR).

RESULTS

GERD increased the risk of developing CRS by 36%, based on the inverse-variance weighted method, a statistically significant association (odds ratio [OR] 1.360, 95% confidence interval [CI] 1.179-1.568, P < 0.001). Other MR assessment methods, such as weighted median, simple mode, and weighted mode, similarly observed a significant increase in the risk of CRS occurrence (OR 1.434, 95% CI 1.186-1.734, P < 0.001; OR 1.927, 95% CI 1.166-3.184, P = 0.013; and OR 1.910, 95% CI 1.222-2.983, P = 0.006, respectively). No significant bias was found in the heterogeneity or pleiotropy tests (P = 0.071 and P = 0.700, respectively). Even after excluding possible mediators using MVMR, GERD appeared to significantly increase the risk of developing CRS (OR 1.013, 95% CI 1.008-1.023, P = 0.002).

CONCLUSIONS

This study provides new, significant evidence that GERD is genetically associated with a higher incidence rate of CRS. However, further research is needed to elucidate the potential underlying biological mechanisms of this relationship.

Higher risk of osteoporosis in adult-onset asthma than childhood-onset asthma: from genetic and prospective evidence

Both COA and AOA have a genetically causal effect on osteoporosis. COA and AOA were independently associated with incident osteoporosis, and the risk was greatly higher in AOA. Besides corticosteroids, the increased risk of osteoporosis among asthma patients should be attributed to genetic susceptibility and other asthma medications.

PURPOSE/INTRODUCTION

Childhood-onset asthma (COA) differs with adult-onset asthma (AOA) on genetic susceptibility, severity, and co-morbidities. Whether COA or AOA is independently associated with osteoporosis is unexplored. We aimed to determine the effects of COA and AOA on osteoporosis at genetic and individual level.

METHODS

We used two-sample Mendelian randomization analysis to explore the causal effects of COA and AOA on osteoporosis. In the UK Biobank cohort, we included 478,289 osteoporosis-free participants at baseline (2006-2010). Participants were classified as non-asthma, COA, and AOA at recruitment. Multivariate Cox regression analysis was used to evaluate the effects of COA, AOA, and multiple asthma medications on incident osteoporosis risk.

RESULTS

COA and AOA were causally related to osteoporosis, with odds ratio of 1.007 (95% confidence interval (CI), 1.0003-1.0132) and 1.012 (95% CI, 1.002-1.023), respectively. Multivariate Cox regression analysis suggested that COA (hazard ratio (HR), 1.46; 95% CI, 1.32-1.61) and AOA (HR, 1.70; 95% CI, 1.61-1.80) were independently associated with incident osteoporosis, and the risk was greatly higher in AOA (HR, 1.51; 95% CI, 1.34-1.70). In addition to corticosteroids, monotherapy with leukotriene modifiers (HR, 1.70; 95% CI, 1.20-2.42), long-acting beta agonists (HR, 1.49; 95% CI, 1.18-1.87), and short-acting beta agonists (HR, 1.72; 95% CI1.01-2.93) were independently associated with a higher risk of osteoporosis.

CONCLUSIONS

Both COA and AOA have a genetically causal effect on osteoporosis, and the risk of osteoporosis is greatly higher in AOA. Besides corticosteroids, the increased risk of osteoporosis among asthma patients should be attributed to genetic susceptibility and other asthma medications.

Association between lipid-lowering drugs and allergic diseases: A Mendelian randomization study

Background

Several observational studies suggest a possible link between lipid-lowering drugs and allergic diseases. However, inferring causality from these studies can be challenging due to issues such as bias, reverse causation, and residual confounding. To investigate the potential causal effect of lipid-lowering drugs, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors and 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) inhibitors, on allergic diseases (allergic asthma, allergic conjunctivitis, atopic dermatitis, allergic rhinitis, and allergic urticaria), we performed a Mendelian randomization (MR)-based study.

Methods

We employed MR and summary-data-based MR (SMR), analyzing genome-wide association study (GWAS) data from people of European descent. Single nucleotide polymorphisms (SNPs) were employed as instrumental variables. We selected 2 types of genetic measures to represent the impact of lipid-lowering drugs, including genetic variants near or within drug target genes correlated with low-density lipoprotein cholesterol (LDL-C), and expression quantitative trait loci of drug target genes. The inverse-variance weighted (IVW)-MR approach was the primary utilized MR method, while sensitivity analyses were used to test the robustness of the results. We used SMR analysis as a supplementary analytical method, applying the heterogeneity in dependent instruments (HEIDI) test to assess if the observed correlation between gene expression and outcome was due to a linkage situation.

Results

The IVW-MR analysis revealed significant evidence for an association between PCSK9-mediated LDL-C reduction and a decrease in the risk of allergic asthma (odds ratio [OR] = 1.31, 95% confidence interval [CI] = 1.11-1.56; P < 0.01). Likewise, SMR analysis discovered an augmented expression of PCSK9 being linked with a heightened susceptibility to allergic asthma (OR = 1.21, 95% CI = 1.03-1.43; P = 0.02). No consistent evidence was found for other associations in either analysis.

Conclusion

Our findings support a potential causal relationship between PCSK9 activity and an increased risk of allergic asthma. Thus, PCSK9 inhibitors, which reduce PCSK9 activity, might be considered a priority in future clinical trials investigating drugs for allergic asthma prevention or treatment.

Treatable Traits in Asthma: The Importance of Extrapulmonary Traits-GERD, CRSwNP, Atopic Dermatitis, and Depression/Anxiety

Treatable traits is a personalized medicine approach to the management of airway disease. Assessing traits within the 3 domains of pulmonary, extrapulmonary, and behavioral/lifestyle/risk factor traits, and applying targeted treatments to effectively manage these traits, enables a holistic and personalized approach to care. Asthma is a heterogeneous and complex airway disease that is frequently complicated by several extrapulmonary traits that impact asthma outcomes and predict future outcomes. We propose that the identification of extrapulmonary and behavioral risk factor traits and the implementation of targeted therapy will lead to improved management of people with asthma. Furthermore, many extrapulmonary traits present as "connected comorbidities"; that is, they coexist with asthma, have an impact on asthma, and effective treatment improves both asthma and the comorbidity or the comorbidities may share a similar mechanism. In this review, we explore this concept and look at atopic dermatitis, chronic rhinosinusitis with nasal polyps, gastroesophageal reflux disease, anxiety, and depression as treatable traits of asthma and how these can be managed using this approach.

Causal relationship between irritability and asthma: a bidirectional two-sample Mendelian randomization study

INTRODUCTION

Previous studies have suggested a relationship between bad mood and asthma. Therefore, in this study, a two-sample Mendelian randomization (MR) method was used to explore the correlation between irritability and asthma.

MATERIAL AND METHODS

Relevant instrumental variables (IVs) were extracted from the aggregated data of the genome-wide association studies (GWAS) database. Inverse-variance weighting (IVW) and weighted median (WME) were used for the MR analysis to evaluate the causal relationship between irritability and asthma using odds ratios (ORs) and the corresponding 95% confidence intervals (CIs), respectively. The "leave-one-out" method was used for sensitivity analysis.

RESULTS

The results of IVW analysis using random-effects models suggested that irritability increased the risk of asthma (OR = 1.954, 95% CI = 1.188-3.214, p = 0.008). The results of WME were consistent with this observation (OR = 1.934, 95% CI = 1.100-3.400, p = 0.021). Additionally, gastroesophageal reflux disease (GERD) might account for approximately 40% of the relationship between irritability and asthma. The sensitivity analysis revealed the stability of the results.

CONCLUSION

The causal relationship between irritability and asthma was analyzed through MR analysis. Irritability increased the risk of asthma. GERD might play an important mediating role in this relationship.

Identifying causal relationships between gastroesophageal reflux and extraesophageal diseases: A Mendelian randomization study

Traditional observational and in vivo studies have suggested an etiological link between gastroesophageal reflux disease (GERD) and the development of extraesophageal diseases (EEDs), such as noncardiac chest pain. However, evidence demonstrating potential causal relationships is lacking. This study evaluated the potential causal relationship between GERD and EEDs, including throat and chest pain, asthma, bronchitis, chronic rhinitis, nasopharyngitis and pharyngitis, gingivitis and periodontal disease, cough, using multiple Mendelian randomization (MR) methods, and sensitivity analysis was performed. The Mendelian randomization Pleiotropy RESidual Sum and Outlier and PhenoScanner tools were used to further check for heterogeneous results and remove outliers. MR with inverse-variance weighted (IVW) showed a significant causal relationship between GERD and EEDs after Bonferroni correction. IVW results indicated that GERD increased the risk of chronic rhinitis, nasopharyngitis and pharyngitis (odds ratio [OR] = 1.482, 95% confidence interval [CI] = 1.267-1.734, P < .001], gingivitis and periodontal disease (OR = 1.166, 95% CI = 1.046-1.190, P = .001), throat and chest pain (OR = 1.585, 95% CI = 1.455-1.726, P < .001), asthma (OR = 1.539, 95% CI = 1.379-1.717, P < .001), and bronchitis (OR = 1.249, 95% CI = 1.168-1.335, P < .001). Sensitivity analysis did not detect pleiotropy. Leave-one-out analysis shows that MR results were not affected by individual single nucleotide polymorphisms. The funnel plot considers the genetic instrumental variables to be almost symmetrically distributed. This MR supports a causal relationship among GERD and EEDs. Precise moderation based on causality and active promotion of collaboration among multidisciplinary physicians ensure high-quality diagnostic and treatment recommendations and maximize patient benefit.

Gastrointestinal Comorbidities Associated with Atopic Dermatitis-A Narrative Review

The current understanding of atopic dermatitis (AD) seems to be extending beyond a skin-confined condition frequently associated with allergic comorbidities, as in a number of epidemiological studies, the prevalence rate of a range of illnesses has been determined to be greater in patients with AD, or inversely. In most cases, the reasons for this are vague. A subset of these conditions are gastrointestinal disorders, including food sensitization (FS) and food allergy (FA), eosinophilic esophagitis (EoE) (it is of mixed background, both IgE-dependent and independent), food protein-induced enterocolitis syndrome (FPIES) (it exemplifies an IgE-independent food allergy), Crohn's disease (CD), colitis ulcerosa (CU), celiac disease, irritable bowel syndrome (IBS), and gastroesophageal reflux disease (GERD). In this review, we performed a comprehensive search of the literature using the PubMed database. We addressed the epidemiology of the increased co-occurrence of these diseases with AD and discussed potential causes for this subject. Multiple gastroenterological comorbidities appear to be more common in patients with AD, according to our review. The mechanisms that underlie this phenomenon are largely unknown, highlighting the need for further study in this field.

Causal relationships between atopic dermatitis and psychiatric disorders: a bidirectional two-sample Mendelian randomization study

BACKGROUND

Observational studies have suggested the potential associations between atopic dermatitis (AD) and psychiatric disorders. However, the causal relationship between them remains uncertain. This study aimed to evaluate the potential bidirectional causal relationship between AD and psychiatric disorders, including autism spectrum disorder (ASD), major depressive disorder (MDD), attention deficit hyperactivity disorder (ADHD), bipolar disorder (BD), anorexia nervosa (AN), Tourette syndrome (TS), schizophrenia, and anxiety.

METHODS

Bidirectional two-sample Mendelian randomization (MR) was employed to elucidate the causality between AD and psychiatric disorders, using summary statistics from the most comprehensive genome-wide association studies conducted on AD (Ncases = 60,653, Ncontrols = 804,329). Psychiatric disorders were derived from the Psychiatric Genomics Consortium and were independent of AD data sources. The MR analysis entailed the implementation of multiple methods, including the inverse variance weighted method, MR-Egger regression method, weighted median method, simple mode method, and weighted mode method.

RESULTS

Bidirectional two-sample MR analysis uncovered significant causal associations between AD and severe psychiatric disorders. Specifically, liability to AD was associated with increased risk of ADHD (OR = 1.116; 95% CI: [1.009, 1.234]; P = 0.033) and ASD (OR = 1.131; 95% CI: [1.023, 1.251]; P = 0.016). Additionally, evidence suggested that liability to ADHD (OR = 1.112; 95% CI: [1.094, 1.130]; P = 9.20e-40), liability to AN (OR = 1.1; 95% CI: [1.068, 1.134]; P = 4.45e-10) and liability to BD (OR = 1.067; 95% CI: [1.009, 1.128]; P = 0.023) were associated with an increased risk of AD. Only the causal association between AD and ASD was independent of the reverse effect bias. These causal associations were robust and not affected by biases of heterogeneity and horizontal pleiotropy.

CONCLUSIONS

Our study emphasizes the significant causal association between AD and an increased risk of ASD, and also identifying BD and AN as risk factors for AD.

The causal relationship between risk of developing bronchial asthma and frailty: a bidirectional two-sample Mendelian randomization study

Background

A potential link between asthma and frailty has been suggested in previous studies. However, the nature of the causal relationship between these two conditions warrants further investigation. Therefore, this study assessed the bidirectional causality between asthma and frailty risk using two-sample Mendelian randomization (MR).

Methods

The study data were obtained from the genome-wide association study (GWAS) dataset, with 337,159 samples representing asthma data and 175,226 samples representing frailty. The causal relationship between the two disorders was assessed by selecting the single nucleotide polymorphisms (SNPs), significantly associated with both asthma and frailty. The inverse variance weighting (IVW) method was used as the main analytical method to estimate the possible influence of causality. Sensitivity analysis was also performed using Mr-Egger intercept, funnel plot, "leave-one-out," and Cochran Q test. In addition, potential mediators were investigated by risk factor analysis.

Result

The IVW method showed an increased risk of frailty due to increased genetic susceptibility factors and the number of to asthma (OR = 2.325, 95%CI:1.958-2.761; p = 6.527498e-22), while no horizontal pleiotropy was observed for the Mr-Egger intercept (p = 0.609) and the funnel plot. The Cochran Q value was 72.858, p = 0.024, and there was heterogeneity in the Cochran Q-value. No single SNP was observed for "leave-one-out" that had a biasing effect on the instrumental variables. In addition, genetic susceptibility to frailty was associated with asthma (OR = 1.088, 95%CI:1.058-1.119; p = 4.815589e-09). In the causal relationship described above, several risk factors for frailty are complex, with asthma leading to a significant reduction in physical activity endurance.

Conclusion

Our findings suggest a probable positive causal effect of asthma on the risk of developing frailty, potentially mediated by reduced physical activity endurance. At the same time, a causal relationship exists between frailty and asthma. Therefore, assessment strategies for frailty should include asthma and vice versa.

Common gastrointestinal diseases and chronic obstructive pulmonary disease risk: a bidirectional Mendelian randomization analysis

Background: Observational studies suggest an association between gastrointestinal diseases and chronic obstructive pulmonary disease (COPD), but the causal relationship remains unclear. Methods: We conducted bidirectional Mendelian randomization (MR) analysis using summary data from genome-wide association study (GWAS) to explore the causal relationship between common gastrointestinal diseases and COPD. Gastrointestinal diseases included gastroesophageal reflux disease (GERD), peptic ulcer disease (PUD), irritable bowel syndrome (IBS), Crohn's disease (CD), ulcerative colitis (UC), functional dyspepsia (FD), non-infectious gastroenteritis (NGE), and constipation (CP). Significant MR analysis results were replicated in the COPD validation cohort. Results: Bidirectional MR analysis supported a bidirectional causal relationship between GERD and COPD, and COPD was also found to increase the risk of IBS and CP. Our study also provided evidence for a bidirectional causal relationship between PUD and COPD, although the strength of evidence may be insufficient. Furthermore, we provided evidence that there is no causal association between CD, UC, FD, NGE, and COPD. Conclusion: This study offers some evidence to clarify the causal relationship between common gastrointestinal diseases and COPD. Further research is needed to understand the underlying mechanisms of these associations.

The associations between asthma and common comorbidities: a comprehensive Mendelian randomization study

Background

Asthma is a chronic respiratory disease and is often associated with multiple comorbidities. The causal relationship between asthma and these comorbidities is still unclear. This study aimed to investigate the association between genetically predicted asthma and common comorbidities.

Methods

After searching PubMed and GWAS summary statistics, we identified 26 comorbidities of asthma. The causal relationship between asthma and comorbidities was assessed in two independent GWASs by bidirectional Mendelian randomization, followed by validation of the results using a multivariate Mendelian randomization analysis and several sensitivity analyses.

Results

In the bidirectional Mendelian randomization analysis, chronic sinusitis [odds ratio (OR) = 1.54, p = 1.40 × 10-5], atopic dermatitis (OR = 1.36, p = 9.37 × 10-21), allergic conjunctivitis (OR = 2.07, p = 4.32 × 10-6), and allergic rhinitis (OR = 1.53, p = 5.20 × 10-6) were significantly associated with increased asthma risk. Hyperthyroidism (OR = 1.12, p = 0.04) had a potential increased risk for asthma. For the reverse direction, asthma showed significant associations with an increased risk of chronic obstructive pulmonary disease (OR = 1.24, p = 2.25 × 10-9), chronic sinusitis (OR = 1.61, p = 5.25 × 10-21), atopic dermatitis (OR = 2.11, p = 1.24 × 10-24), allergic conjunctivitis (OR = 1.65, p = 6.66 × 10-35), allergic rhinitis (OR = 1.90, p = 2.38 × 10-57), and a potential higher risk of allergic urticaria (OR = 1.25, p = 0.003).

Conclusion

This study suggested a significant bidirectional association of chronic sinusitis, atopic dermatitis, allergic conjunctivitis, and allergic rhinitis with asthma. In addition, hyperthyroidism was associated with an increased risk of asthma and asthma increased the risk of chronic obstructive pulmonary disease and allergic urticaria.

Potential drug targets for asthma identified in the plasma and brain through Mendelian randomization analysis

Background

Asthma is a heterogeneous disease, and the involvement of neurogenic inflammation is crucial in its development. The standardized treatments focus on alleviating symptoms. Despite the availability of medications for asthma, they have proven to be inadequate in controlling relapses and halting the progression of the disease. Therefore, there is a need for novel drug targets to prevent asthma.

Methods

We utilized Mendelian randomization to investigate potential drug targets for asthma. We analyzed summary statistics from the UK Biobank and then replicated our findings in GWAS data by Demenais et al. and the FinnGen cohort. We obtained genetic instruments for 734 plasma and 73 brain proteins from recently reported GWAS. Next, we utilized reverse causal relationship analysis, Bayesian co-localization, and phenotype scanning as part of our sensitivity analysis. Furthermore, we performed a comparison and protein-protein interaction analysis to identify causal proteins. We also analyzed the possible consequences of our discoveries by the given existing asthma drugs and their targets.

Results

Using Mendelian randomization analysis, we identified five protein-asthma pairs that were significant at the Bonferroni level (P < 6.35 × 10-5). Specifically, in plasma, we found that an increase of one standard deviation in IL1R1 and ECM1 was associated with an increased risk of asthma, while an increase in ADAM19 was found to be protective. The corresponding odds ratios were 1.03 (95% CI, 1.02-1.04), 1.00 (95% CI, 1.00-1.01), and 0.99 (95% CI, 0.98-0.99), respectively. In the brain, per 10-fold increase in ECM1 (OR, 1.05; 95% CI, 1.03-1.08) and PDLIM4 (OR, 1.05; 95% CI, 1.04-1.07) increased the risk of asthma. Bayesian co-localization found that ECM1 in the plasma (coloc.abf-PPH4 = 0.965) and in the brain (coloc.abf-PPH4 = 0.931) shared the same mutation with asthma. The target proteins of current asthma medications were found to interact with IL1R1. IL1R1 and PDLIM4 were validated in two replication cohorts.

Conclusion

Our integrative analysis revealed that asthma risk is causally affected by the levels of IL1R1, ECM1, and PDLIM4. The results suggest that these three proteins have the potential to be used as drug targets for asthma, and further investigation through clinical trials is needed.

Management of comorbidities in difficult and severe asthma

Difficult-to-treat and severe asthma are challenging clinical entities. In the face of suboptimal asthma control, the temptation for clinicians is to reflexively escalate asthma-directed therapy, including increasing exposure to corticosteroids and commencement of costly but potent biologic therapies. However, asthma control is objectively and subjectively assessed based on measurable parameters (such as exacerbations or variability in pulmonary physiology), symptoms and patient histories. Crucially, these features can be confounded by common untreated comorbidities, affecting clinicians' assessment of asthma treatment efficacy.

Asthma and atopic dermatitis as risk factors for rheumatoid arthritis: a bidirectional mendelian randomization study

BACKGROUND

Previous observational studies have shown an association between asthma, atopic dermatitis (AD) and rheumatoid arthritis (RA). However, the bidirectional cause-effect chain between asthma and AD and RA has not been proven yet.

METHODS

We performed bidirectional two-sample Mendelian randomization (TSMR) and selected single nucleotide polymorphisms (SNPs) associated with asthma, AD, and RA as instrumental variables. All of the SNPs were obtained from the latest genome-wide association study in Europeans. Inverse variance weighted (IVW) was the main method used in MR analysis. MR-Egger, weighted model, simple model, and weighted median were used for quality control. The robustness of the results was tested by sensitivity analysis.

RESULTS

Asthma was found to be the largest effect size for RA susceptibility using the IVW method (OR, 1.35;95%CI, 1.13-1.60; P, 0.001), followed by AD (OR, 1.10;95%CI, 1.02-1.19; P, 0.019). In contrast, there was no causal relationship between RA and asthma (IVW: P = 0.673) or AD (IVW: P = 0.342). No pleiotropy or heterogeneity was found in the sensitivity analysis.

CONCLUSION

Findings from this study showed a causal relationship between genetic susceptibility to asthma or AD and increased risk of RA, but do not support a causal relationship between genetic susceptibility to RA and asthma or AD.

Association of atopic dermatitis with autoimmune diseases: A bidirectional and multivariable two-sample mendelian randomization study

Background

Observational studies have suggested the association between atopic dermatitis (AD) and the risks of autoimmune diseases. It is still unclear, however, whether or in which direction causal relationships exist, because these associations could be confounded.

Objectives

Our study seeks to assess the possibility of AD as a cause of autoimmune diseases, and to estimate the magnitude of the causal effect.

Methods

Two-sample mendelian randomization (MR) analyses were performed using genome-wide association study (GWAS) summary-level statistics. Specifically, bidirectional MR analyses were conducted to examine the direction of association of AD with autoimmune diseases; multivariable MR analyses (MVMR1) were used to test the independence of causal association of AD with autoimmune diseases after controlling other atopic disorders (asthma and allergic rhinitis), while MVMR2 analyses were conducted to account for potential confounding factors such as smoking, drinking, and obesity. Genetic instruments for AD (Ncases=22 474) were from the latest GWAS meta-analysis. The GWAS summary data for asthma and allergic rhinitis were obtained from UK Biobank. The GWAS summary data for smoking, alcohol consumption, obesity and autoimmune diseases (alopecia areata, vitiligo, systemic lupus erythematosus, ankylosing spondylitis, rheumatoid arthritis, and type 1 diabetes) were selected from the largest GWASs available. Causal estimates were derived by the inverse-variance weighted method and verified through a series of sensitivity analyses.

Results

Genetically predicted AD linked to higher risks of rheumatoid arthritis (OR, 1.28; P=0.0068) (OR_MVMR1, 1.65; P=0.0020) (OR_MVMR2, 1.36; P<0.001), type 1 diabetes (OR, 1.37; P=0.0084) (OR_MVMR1, 1.42; P=0.0155) (OR_MVMR2, 1.45; P=0.002), and alopecia areata (OR, 1.98; P=0.0059) (OR_MVMR1, 2.55; P<0.001) (OR_MVMR2, 1.99; P=0.003) in both univariable and multivariable MR. These causal relationships were supported by sensitivity analyses. No causal effect of AD was identified in relation to systemic lupus erythematosus, vitiligo, and ankylosing spondylitis. Concerning the reverse directions, no significant association was noted.

Conclusion

The results of this MR study provide evidence to support the idea that AD causes a greater risk of rheumatoid arthritis, type 1 diabetes and alopecia areata. Further replication in larger samples is needed to validate our findings, and experimental studies are needed to explore the underlying mechanisms of these causal effects.