Dermatology: Practical and Conceptual Review | Dermatol Pract Concept. 2022;12(4):e2022165 1 Association Between Atopic Dermatitis and Major Cardiovascular Outcomes: a Two-Sample Mendelian Randomization Study Hongjiao Qi1, Lifeng Wang2, Linfeng Li1 1 Department of Dermatology, Beijing Friendship Hospital, Capital Medical University, Beijing, PR China 2 Department of Dermatology, Beijing Luhe Hospital, Capital Medical university, Beijing, PR China Key words: atopic dermatitis, cardiovascular disease, Mendelian randomization Citation: Qi H, Wang L, Li L. Association between Atopic Dermatitis and Major Cardiovascular Outcomes: A Two-Sample Mendelian Randomization Study. Dermatol Pract Concept. 2022;12(4):e2022165. DOI: https://doi.org/10.5826/dpc.1204a165 Accepted: February 28, 2022; Published: October 2022 Copyright: ©2022 Qi et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding author: Linfeng Li, Department of Dermatology, Beijing Friendship Hospital, Capital Medical University, Beijing, PR China, Address: 95 Yong’an Road, Xicheng District, Beijing, China. Zip: 100050, Tel: +8613693620186, E-mail: zoonli@sina.com Introduction: Atopic dermatitis (AD) has been linked to cardiovascular disease (CVD) in population-based studies, however, their causal relationship is still unclear. Objectives: To evaluate the causal association of AD with risk of cardiovascular outcomes using a Mendelian randomization (MR) approach. Methods: We extracted summary-level data for AD, stroke, heart failure, coronary artery disease (CAD), myocardial infarction, angina pectoris from published, nonoverlapping genome-wide asso- ciation studies (GWAS). Inverse variance weighted (IVW) method was used as the primary analysis. Alternative methods, including weighted median, MR Egger, MR-Pleiotropy Residual Sum and Outlier, weighted mode, and leave-out analysis, were performed to examine potential pleiotropy. Results: Thirteen SNPs (13,287 cases and 41,345 controls) were selected as instrumental variables (IVs). No associations of AD with risks of stroke (odds ratio [OR] = 1.03, 95% confidence interval [CI]: 0.97-1.09, P = 0.3630), heart failure (OR = 1.04, 95%CI: 0.99-1.09, P= 0.119), coronary ar- tery disease (OR = 1.00, 95%CI: 0.96-1.05, P = 0.988), myocardial infarction (OR = 1.00, 95%CI: 1.00-1.00, P = 0.322), and angina pectoris (OR = 1.00, 95%CI: 1.00-1.00, P = 0.369) was found. No significant effect of pleiotropy was detected. Conclusions: This MR study does not support a causal effect of AD on stroke, heart failure, CAD, myocardial infarction, angina pectoris. ABSTRACT 2 Review | Dermatol Pract Concept. 2022;12(4):e2022165 Introduction Atopic dermatitis (AD, atopic eczema, eczema) is a common chronic, inflammatory, relapsing, skin diseases [1]. The prev- alence of AD is 15 to 20% among children And 7% to 14% among adults [2,3]. It is characterized by eczematous lesions, varying degrees of pruritus, and a chronic or relapsing disease course [4]. AD broadly decreases health-related quality of life [5]. Recently, there has been a growing interest in the puta- tive cardiovascular comorbidities of AD in population-based observational studies [6-11]. However, owning to the nature of being susceptible to potential confounders and reverse causation in observational study design [12], it remains un- clear whether the elevated risk of CVD in patients with AD is caused by AD or introduced by confounding factors of AD and CVD. Understanding the causal relationship between AD and CVD could have implications for appropriate iden- tification, clinical surveillance, and management of high-risk population. Mendelian randomization (MR) analysis is a novel epidemiological approach to assess the causal relation- ship between an exposure and an outcome [12], with less sus- ceptibility to unmeasured confounders and reverse causation by using genetic variants (i.e., single nucleotide polymor- phisms, SNPs) as instrumental variables (IVs) [13,14]. Objectives In this study, we explored the causal associations between AD and CVD events using the MR method. Methods We carried out a two-sample MR analysis based on sum- mary statistics to investigate the causal relationship between AD and CVD events including stroke, heart failure, CAD, myocardial infarction, and angina pectoris. Single nucleotide polymorphisms (SNPs) were selected as instruments vari- ables because they are randomly allocated and less probable to be affected by confounding or reverse causation[15]. We used publicly available data, informed patients consents and ethical approvals were available in original genome-wide as- sociation studies (GWAS) studies. Data Sources and Selection of SNPs Summary-level data for AD were extracted from the EArly Genetics and Lifecourse Epidemiology (EAGLE) eczema consortium, including 13,287 cases and 41,345 controls of mostly European ancestry [16]. Summary-level data stroke were extracted from the MEGASTROKE Consortium, a meta-analysis of 29 GWAS including a total of 40,585 cases and 406,111 non-cases of European ancestry [17]. Summary-level data for heart failure were extracted from the Heart Failure Molecular Epidemiology for Therapeutic Targets (HERMES) Consortium [18], comprising 47,309 cases and 930,014 non-cases of European ancestry across 26 studies. Summary-level data for CAD from UKBiobank- CardioMetabolic-Consortium CHD working group in- cluded 10801 cases and 137914 non-cases of European ancestry [19]. Summary-level data for myocardial infarction from UKBiobank included 4837 cases and 332,362 non- cases of European ancestry. Summary-level data for angina pectoris from UKBiobank included 4,837 cases and 332,362 non-cases of European ancestry. Statistical Analysis For each CVD outcome, we carried out two-sample MR anal- ysis to estimate the causal effect of AD, using the “TwoSam- pleMR” package of R. The inverse-variance weighted (IVW) linear regression was conducted as the primary analysis. IVW is an efficient analysis method which assumes that all genetic variants are valid IVs, and that there is no horizon- tal pleiotropy [20]. We calculated the odds ratio (OR) with 95% confidence interval (CI) and created the SNP effect scatter plot. Besides, we assessed the potential violations of the as- sumptions of MR analysis by performing a number of com- plementary sensitivity analysis: weighted median approach for examining result robustness when some instruments may be potentially invalid [20], MR-Egger regression for evaluating the directional pleiotropy of instruments [21,22], weighted mode, which generally has low bias and low Type 1 error rate inflation [23], MR Pleiotropy RESidual Sum and Outlier (MR PRESSO) for outlier instrument detection [24], and leave-one-out analysis to evaluate whether the MR esti- mate was influenced by single proxy SNP. We also calculated the Cochran Q test from the IVW analysis to examine poten- tial horizontal pleiotropy. All statistical analyses were performed using R software 4.0.3 (R Foundation for Statistical Computing). All statisti- cal tests were two-sided with α=0.05. Results Genetic Instruments Thirteen SNPs were identified as associated with AD (P<5×10-8), with independent inheritance (r2<0.01), and without linkage disequilibrium (LD) in summary statistics. All of these 13 SNPs were available in GWAS for stroke, heart failure, CAD, myocardial infarction, angina pectoris. Details of the included SNPs are shown in Tables S1, Tables S2, S3, S4, and S5 respectively. Review | Dermatol Pract Concept. 2022;12(4):e2022165 3 Two-sample MR of AD and CVD No significant evidence was found for a causal effect of AD on stroke, heart failure, CAD, myocardial infarction, angina pectoris using the IVW analysis (stroke: OR = 1.03, 95%CI: 0.97-1.09, P = 0.363; heart failure: OR = 1.04, 95%CI: 0.99-1.09, P = 0.119; CAD: OR = 1.00, 95%CI: 0.94-1.06, P = 0.961; myocardial infarction: OR = 1.00, 95%CI: 1.00- 1.00, P = 0.322; angina pectoris: OR = 1.00, 95%CI: 1.00- 1.00, P = 0.369). The results neither weighted median, MR Egger, weighted mode nor MR PRESSO analyses were sig- nificant for all of the diseases above (Table 1 and Figures S1, S2, S3, S4, S5). Leave-one-out analysis indicated no influence of single SNP on the risk estimates of AD on stroke, heart failure, CAD, myocardial infarction, angina pectoris. P values of Co- chrane Q test and MR Egger intercept for AD on stroke were 0.481 and 0.695, respectively; for AD on heart failure were 0.150 and 0.224, respectively; for AD on CAD were 0.146 and 0.583, respectively; for AD on myocardial infarction were 0.417 and 0.993, respectively; for AD on angina pec- toris were 0.080 and 0.752, respectively, suggesting no evi- dence of potential horizontal pleiotropy and heterogeneity. Conclusions To the best of our knowledge, this is the first study to explore the causal relationship between AD and CVD based on an MR approach. Our results did not support a causal effect of AD on CVD. Previous studies on the link between AD and stroke are controversial. In a Danish matched cohort study, patients with severe AD had an increased risk of ischemic stroke, but after adjustment for socioeconomic status, smoking, co- morbidities, and medication use, the risk was similar with controls [6]. In a cohort from the Nurses’ Health Study 2, the risk of stroke was significantly increased in female nurses with AD in the age and models adjusted for demo- graphic, lifestyle risk factors, family history of MI, and Table 1. The Causal Effect of Atopic Dermatitis on Stroke Type of CVD Method OR (95% CI) P Value No. of SNPs Stroke IVW 1.03 (0.97-1.09) 0.363 13 Weighted median 0.99 (0.92-1.05) 0.681 13 MR Egger 0.96 (0.79-1.17) 0.694 13 Weighted mode 0.97 (0.88-1.07) 0.529 13 MR PRESSO 1.01 (0.96-1.06) 0.659 13 Heart failure IVW 1.04 (0.99-1.09) 0.119 13 Weighted median 1.05 (1.00-1.11) 0.069 13 MR Egger 1.13 (0.98-1.30) 0.110 13 Weighted mode 1.06 (0.98-1.14) 0.176 13 MR PRESSO 1.04 (0.99-1.09) 0.145 13 Coronary artery disease IVW 1.00 (0.96-1.05) 0.988 13 Weighted median 0.99 (0.94-1.05) 0.760 13 MR Egger 0.96 (0.84-1.10) 0.608 13 Weighted mode 0.98 (0.90-1.07) 0.654 13 MR PRESSO 1.00 (0.96-1.05) 0.988 13 Myocardial infarction IVW 1.00 (1.00-1.00) 0.322 13 Weighted median 1.01 (1.00-1.00) 0.789 13 MR Egger 1.00 (1.00-1.00 0.724 13 Weighted mode 1.00 (1.00-1.00) 0.574 13 MR PRESSO 1.00 (1.00-1.00) 0.328 13 Angina pectoris IVW 1.00 (1.00-1.00) 0.369 13 Weighted median 1.01 (1.00-1.00) 0.416 13 MR Egger 1.00 (1.00-1.00) 0.992 13 Weighted mode 1.00 (1.00-1.00) 0.627 13 MR PRESSO 1.00 (1.00-1.00) 0.386 13 CI = Confidence interval; CVD = cardiovascular disease; IVW = inverse variance–weighted; MR = mendelian randomization; OR = odds ratio; SNP = single-nucleotide polymorphism. 4 Review | Dermatol Pract Concept. 2022;12(4):e2022165 There are some limitations to the present study. First, the summary-level GWAS data we used were based mainly on people of European ancestry. Therefore, results in this study may not be applicable to other populations. Second, onset age and disease severity of AD might influence the associa- tion between AD and comorbidities, but because the limita- tion of data, we were not able to perform subgroup analyses by age and severity of AD. Third, an important limitation for MR study is potential pleiotropy. In this study, we applied various MR approaches to test for potential pleiotropy, and no evidence of pleiotropy for all the analyses was observed. Moreover, the definitions of AD and comorbidities used in the data is a mixture of self-reported diagnosis together with doctor diagnosed cases, which may cause bias to our findings. Conclusion In conclusion, MR study does not support a causal effect of AD on stroke, heart failure, CAD, myocardial infarction, angina pectoris. References 1. Puar N, Chovatiya R, Paller AS. 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