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      Evidence of a causal relationship between body mass index and psoriasis: A mendelian randomization study

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          Abstract

          Background

          Psoriasis is a common inflammatory skin disease that has been reported to be associated with obesity. We aimed to investigate a possible causal relationship between body mass index (BMI) and psoriasis.

          Methods and findings

          Following a review of published epidemiological evidence of the association between obesity and psoriasis, mendelian randomization (MR) was used to test for a causal relationship with BMI. We used a genetic instrument comprising 97 single-nucleotide polymorphisms (SNPs) associated with BMI as a proxy for BMI (expected to be much less confounded than measured BMI). One-sample MR was conducted using individual-level data (396,495 individuals) from the UK Biobank and the Nord-Trøndelag Health Study (HUNT), Norway. Two-sample MR was performed with summary-level data (356,926 individuals) from published BMI and psoriasis genome-wide association studies (GWASs). The one-sample and two-sample MR estimates were meta-analysed using a fixed-effect model. To test for a potential reverse causal effect, MR analysis with genetic instruments comprising variants from recent genome-wide analyses for psoriasis were used to test whether genetic risk for this skin disease has a causal effect on BMI.

          Published observational data showed an association of higher BMI with psoriasis. A mean difference in BMI of 1.26 kg/m 2 (95% CI 1.02–1.51) between psoriasis cases and controls was observed in adults, while a 1.55 kg/m 2 mean difference (95% CI 1.13–1.98) was observed in children. The observational association was confirmed in UK Biobank and HUNT data sets. Overall, a 1 kg/m 2 increase in BMI was associated with 4% higher odds of psoriasis (meta-analysis odds ratio [OR] = 1.04; 95% CI 1.03–1.04; P = 1.73 × 10 −60). MR analyses provided evidence that higher BMI causally increases the odds of psoriasis (by 9% per 1 unit increase in BMI; OR = 1.09 (1.06–1.12) per 1 kg/m 2; P = 4.67 × 10 −9). In contrast, MR estimates gave little support to a possible causal effect of psoriasis genetic risk on BMI (0.004 kg/m 2 change in BMI per doubling odds of psoriasis (−0.003 to 0.011). Limitations of our study include possible misreporting of psoriasis by patients, as well as potential misdiagnosis by clinicians. In addition, there is also limited ethnic variation in the cohorts studied.

          Conclusions

          Our study, using genetic variants as instrumental variables for BMI, provides evidence that higher BMI leads to a higher risk of psoriasis. This supports the prioritization of therapies and lifestyle interventions aimed at controlling weight for the prevention or treatment of this common skin disease. Mechanistic studies are required to improve understanding of this relationship.

          Abstract

          In a mendelian randomization study, Ashley Budu-Aggrey and co-workers study the influence of body mass index on psoriasis.

          Author summary

          Why was this study done?
          • Psoriasis is a common inflammatory skin disease that has been reported to be associated with obesity. However, the direction of causality has not been established.

          • Understanding the causal relationship could inform the management or prevention of disease.

          What did the researchers do and find?
          • A mendelian randomization (MR) approach was used to investigate the causal relationship between higher body mass index (BMI) and psoriasis.

          • Our analysis included data for a total of 753,421 individuals from two of the largest population-based studies available as well as published genome-wide association studies (GWASs).

          • We found evidence that higher BMI causally increases the risk of psoriasis, supporting observational reports in previous literature.

          • Conversely, there was no evidence to support a causal effect of psoriasis genetic risk upon BMI.

          What do these findings mean?
          • Our findings suggest that obesity contributes to the pathogenesis of psoriasis, and highlight possible mechanistic relationships.

          • If our findings regarding genetically influenced BMI can be extended to elevated BMI that is amenable to modification by diet or behavior, then they could carry health implications.

          • Further work will be required to determine the effect of a short-term intervention aimed at reducing BMI upon psoriasis patients after disease onset, ideally within a clinical trial setting.

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          Most cited references28

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          Using published data in Mendelian randomization: a blueprint for efficient identification of causal risk factors

          Finding individual-level data for adequately-powered Mendelian randomization analyses may be problematic. As publicly-available summarized data on genetic associations with disease outcomes from large consortia are becoming more abundant, use of published data is an attractive analysis strategy for obtaining precise estimates of the causal effects of risk factors on outcomes. We detail the necessary steps for conducting Mendelian randomization investigations using published data, and present novel statistical methods for combining data on the associations of multiple (correlated or uncorrelated) genetic variants with the risk factor and outcome into a single causal effect estimate. A two-sample analysis strategy may be employed, in which evidence on the gene-risk factor and gene-outcome associations are taken from different data sources. These approaches allow the efficient identification of risk factors that are suitable targets for clinical intervention from published data, although the ability to assess the assumptions necessary for causal inference is diminished. Methods and guidance are illustrated using the example of the causal effect of serum calcium levels on fasting glucose concentrations. The estimated causal effect of a 1 standard deviation (0.13 mmol/L) increase in calcium levels on fasting glucose (mM) using a single lead variant from the CASR gene region is 0.044 (95 % credible interval −0.002, 0.100). In contrast, using our method to account for the correlation between variants, the corresponding estimate using 17 genetic variants is 0.022 (95 % credible interval 0.009, 0.035), a more clearly positive causal effect. Electronic supplementary material The online version of this article (doi:10.1007/s10654-015-0011-z) contains supplementary material, which is available to authorized users.
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            Psoriasis and systemic inflammatory diseases: potential mechanistic links between skin disease and co-morbid conditions.

            Psoriasis is now classified as an immune-mediated inflammatory disease (IMID) of the skin. It is being recognized that patients with various IMIDs, including psoriasis, are at higher risk of developing "systemic" co-morbidities, e.g., cardiovascular disease (CVD), metabolic syndrome, and overt diabetes. In non-psoriatic individuals, the pathophysiology of obesity, aberrant adipocyte metabolism, diabetes, and CVDs involves immune-mediated or inflammatory pathways. IMIDs may impact these co-morbid conditions through shared genetic risks, common environmental factors, or common inflammatory pathways that are co-expressed in IMIDs and target organs. Given that pathogenic immune pathways in psoriasis are now well worked out and a large number of inflammatory mediators have been identified in skin lesions, in this review we will consider possible mechanistic links between skin inflammation and increased risks of (1) obesity or metabolic alterations and (2) CVD. In particular, we will discuss how well-established risk factors for CVD can originate from inflammation in other tissues.
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              Genome-wide genetic data on ~500,000 UK Biobank participants

              The UK Biobank project is a large prospective cohort study of ~500,000 individuals from across the United Kingdom, aged between 40-69 at recruitment. A rich variety of phenotypic and health-related information is available on each participant, making the resource unprecedented in its size and scope. Here we describe the genome-wide genotype data (~805,000 markers) collected on all individuals in the cohort and its quality control procedures. Genotype data on this scale offers novel opportunities for assessing quality issues, although the wide range of ancestries of the individuals in the cohort also creates particular challenges. We also conducted a set of analyses that reveal properties of the genetic data (such as population structure and relatedness) that can be important for downstream analyses. In addition, we phased and imputed genotypes into the dataset, using computationally efficient methods combined with the Haplotype Reference Consortium (HRC) and UK10K haplotype resource. This increases the number of testable variants by over 100-fold to ~96 million variants. We also imputed classical allelic variation at 11 human leukocyte antigen (HLA) genes, and as a quality control check of this imputation, we replicate signals of known associations between HLA alleles and many common diseases. We describe tools that allow efficient genome-wide association studies (GWAS) of multiple traits and fast phenome-wide association studies (PheWAS), which work together with a new compressed file format that has been used to distribute the dataset. As a further check of the genotyped and imputed datasets, we performed a test-case genome-wide association scan on a well-studied human trait, standing height.
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                Author and article information

                Contributors
                Role: Data curationRole: Formal analysisRole: InvestigationRole: Writing – original draftRole: Writing – review & editing
                Role: Data curationRole: Formal analysisRole: Writing – original draftRole: Writing – review & editing
                Role: Formal analysisRole: InvestigationRole: Writing – review & editing
                Role: Data curationRole: Formal analysisRole: InvestigationRole: Writing – original draftRole: Writing – review & editing
                Role: Formal analysisRole: Writing – review & editing
                Role: InvestigationRole: Writing – review & editing
                Role: InvestigationRole: Writing – original draftRole: Writing – review & editing
                Role: InvestigationRole: Writing – review & editing
                Role: Formal analysisRole: MethodologyRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: InvestigationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: InvestigationRole: Writing – review & editing
                Role: InvestigationRole: Writing – review & editing
                Role: Data curationRole: Writing – review & editing
                Role: MethodologyRole: Writing – review & editing
                Role: ConceptualizationRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: SupervisionRole: Writing – review & editing
                Role: ConceptualizationRole: SupervisionRole: Writing – review & editing
                Role: Academic Editor
                Journal
                PLoS Med
                PLoS Med
                plos
                plosmed
                PLoS Medicine
                Public Library of Science (San Francisco, CA USA )
                1549-1277
                1549-1676
                31 January 2019
                January 2019
                : 16
                : 1
                : e1002739
                Affiliations
                [1 ] Medical Research Council (MRC) Integrative Epidemiology Unit, University of Bristol, Bristol, United Kingdom
                [2 ] Bristol Medical School, Population Health Sciences, University of Bristol, Bristol, United Kingdom
                [3 ] K.G. Jebsen Center for Genetic Epidemiology, Department of Public Health and Nursing, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
                [4 ] Department of Thoracic Medicine, St. Olavs Hospital, Trondheim University Hospital, Trondheim, Norway
                [5 ] Genetics of Complex Traits, Institute of Biomedical and Clinical Science, University of Exeter Medical School, Royal Devon and Exeter Hospital, Exeter, United Kingdom
                [6 ] European Centre for Environment and Human Health, University of Exeter Medical School, The Knowledge Spa, Truro, United Kingdom
                [7 ] Department of Public Health and Nursing, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
                [8 ] Department of Dermatology, St. Olav’s Hospital, Trondheim University Hospital, Trondheim, Norway
                [9 ] Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
                [10 ] Department of Mathematics and Statistics, Lancaster University, Lancaster, United Kingdom
                [11 ] Department of Internal Medicine, Division of Cardiology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
                [12 ] Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, Michigan, United States of America
                [13 ] Department of Dermatology, University of Michigan, Ann Arbor, Michigan, United States of America
                [14 ] Department of Biostatistics, Center for Statistical Genetics, University of Michigan, Ann Arbor, Michigan, United States of America
                [15 ] Department of Clinical and Molecular Medicine, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
                [16 ] Institute of Infection, Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
                [17 ] Ann Arbor Veterans Affairs Hospital, Ann Arbor, Michigan, United States of America
                [18 ] Department of Endocrinology, St. Olav’s Hospital, Trondheim University Hospital, Trondheim, Norway
                [19 ] Skin Research Group, School of Medicine, University of Dundee, Dundee, United Kingdom
                [20 ] Department of Dermatology, Ninewells Hospital and Medical School, Dundee, United Kingdom
                King’s College London, UNITED KINGDOM
                Author notes

                I have read the journal’s policy and the authors of this manuscript have the following competing interests: IBM has received grants from Arthritis Research UK during the conduct of the study; grants and personal fees from Novartis, grants and personal fees from Janssen, grants and personal fees from Celgene, grants and personal fees from Abbvie, grants from BI, grants and personal fees from UCB, personal fees from Lilly, grants and personal fees from BMS. LP has received personal fees from Merck for Scientific Input Engagement related to MR methodology. SS has received grants from Arthritis Research UK during the conduct of the study; research grants from Janssen, BMS, Celgene, UCB, Boehringer Ingelheim and consultancy/speaker’s fees from AbbVie, UCB, Celgene, Pfizer, Janssen, Boehringer Ingelheim, and Novartis. SJB has received honoraria for invited lectures at the British Association of Dermatologists’ annual meetings and the AAAAI annual meetings. GDS is a member of the Editorial Board of PLOS Medicine.

                ‡These authors are joint last authors on this work.

                Author information
                http://orcid.org/0000-0002-8911-2492
                http://orcid.org/0000-0002-9256-6065
                http://orcid.org/0000-0002-8034-8095
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                http://orcid.org/0000-0003-2612-3917
                http://orcid.org/0000-0002-6136-8349
                http://orcid.org/0000-0003-1552-5291
                http://orcid.org/0000-0003-4655-4511
                http://orcid.org/0000-0002-2110-1690
                http://orcid.org/0000-0002-6654-2852
                http://orcid.org/0000-0001-7719-0859
                http://orcid.org/0000-0003-1627-5722
                http://orcid.org/0000-0003-0153-922X
                http://orcid.org/0000-0003-0750-8248
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                http://orcid.org/0000-0002-3232-5251
                http://orcid.org/0000-0003-2514-0889
                Article
                PMEDICINE-D-18-02371
                10.1371/journal.pmed.1002739
                6354959
                30703100
                d41c81c5-daf4-44a9-a510-b7b96dddd027
                © 2019 Budu-Aggrey et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 2 July 2018
                : 27 December 2018
                Page count
                Figures: 4, Tables: 1, Pages: 18
                Funding
                Funded by: British Heart Foundation
                Award ID: RE/13/5/30177
                Award Recipient :
                Funded by: British Skin Foundation (GB)
                Award ID: 8010 Innovative Project
                Award Recipient :
                Funded by: UK Medical Research Council
                Award ID: MC_UU_00011/1
                Award Recipient :
                Funded by: European Regional Development Fund (ERDF)
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/501100000273, Diabetes Research & Wellness Foundation;
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/100004440, Wellcome Trust;
                Award Recipient :
                Funded by: Royal Society
                Award ID: 104150/Z/14/Z
                Award Recipient :
                Funded by: UK Medical Research Council
                Award ID: MR/M005070/1
                Award Recipient :
                Funded by: European Research Council
                Award ID: 323195:GLUCOSEGENES-FP7-IDEAS-ERC
                Award Recipient :
                Funded by: Stiftelsen Kristian Gerhard Jebsen; Faculty of Medicine and Health Sciences, NTNU
                Award Recipient :
                Funded by: The Liaison Committee for education, research and innovation in Central Norway
                Award Recipient :
                Funded by: the Joint Research Committee between St. Olavs hospital and the Faculty of Medicine and Health Sciences, NTNU
                Award Recipient :
                Funded by: Norwegian Research Council
                Award ID: 250335
                Award Recipient :
                Funded by: Danish Heart Foundation
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/100004440, Wellcome Trust;
                Award ID: 106865/Z/15/Z
                Award Recipient :
                Funded by: British Heart Foundation
                Award ID: RE/13/5/30177
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/100000002, National Institutes of Health;
                Award Recipient :
                Funded by: University of Michigan
                Funded by: The Research Council of Norway
                AB-A and LP are funded by a grant awarded by the British Skin Foundation (8010 Innovative Project) ( http://www.britishskinfoundation.org.uk/). AB-A, LP, SW, and GDS work in a research unit funded by the UK Medical Research Council (MC_UU_00011/1) ( https://mrc.ukri.org/). JT is funded by the European Regional Development Fund (ERDF) ( http://ec.europa.eu/regional_policy/en/funding/erdf/) and a Diabetes Research and Wellness Foundation fellowship ( https://www.drwf.org.uk/). RNB is funded by the Wellcome Trust ( https://wellcome.ac.uk/) and Royal Society grant 104150/Z/14/Z ( https://royalsociety.org). SEJ is funded by the Medical Research Council (grant MR/M005070/1) ( https://mrc.ukri.org/). JT, RNB, and SEJ’s analysis of UK Biobank was under project 9072. TMF and ARW are supported by the European Research Council (grant 323195:GLUCOSEGENES-FP7-IDEAS-ERC) ( https://erc.europa.eu/). BB, ML, LGF, and BOA work in a research unit funded by Stiftelsen Kristian Gerhard Jebsen; Faculty of Medicine and Health Sciences, NTNU ( https://stiftkgj.no/what-we-do/k-g-jebsen-centres-of-medical-research/?lang=en); The Liaison Committee for education, research and innovation in Central Norway ( https://helsemidt.no/helsefaglig/helsefaglig/samarbeidsorganet); and the Joint Research Committee between St. Olav’s Hospital and the Faculty of Medicine and Health Sciences, NTNU ( https://www.ntnu.edu/). EHM and ML were supported by a research grant from the Liaison Committee for education, research and innovation in Central Norway ( https://helsemidt.no/helsefaglig/helsefaglig/samarbeidsorganet). GAV is supported by a research grant from the Norwegian Research Council, grant number 250335 ( https://www.forskningsradet.no/en/Home_page/1177315753906). JBN was supported by grants from the Danish Heart Foundation ( https://hjerteforeningen.dk/english/) and the Lundbeck Foundation ( https://www.lundbeckfonden.com/en/). SJB holds a Wellcome Trust Senior Research Fellowship in Clinical Science (106865/Z/15/Z) ( https://wellcome.ac.uk/). LDF is funded by the British Heart Foundation (BHF) Research Excellence award, grant number RE/13/5/30177 ( https://www.bhf.org.uk/for-professionals/information-for-researchers/what-we-fund). The genotyping in HUNT was financed by the National Institutes of Health (NIH) ( https://www.nih.gov/); the University of Michigan ( https://www.umich.edu/); The Research Council of Norway ( https://www.forskningsradet.no/en/Home_page/1177315753906); The Liaison Committee for education, research and innovation in Central Norway ( https://helsemidt.no/helsefaglig/helsefaglig/samarbeidsorganet); and the Joint Research Committee between St. Olav’s hospital and the Faculty of Medicine and Health Sciences, NTNU ( https://www.ntnu.edu/). The psoriasis meta-GWAS was funded by multiple sources, including the NIH ( https://www.nih.gov/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Medicine and Health Sciences
                Clinical Medicine
                Clinical Immunology
                Autoimmune Diseases
                Psoriasis
                Biology and Life Sciences
                Immunology
                Clinical Immunology
                Autoimmune Diseases
                Psoriasis
                Medicine and Health Sciences
                Immunology
                Clinical Immunology
                Autoimmune Diseases
                Psoriasis
                Biology and Life Sciences
                Physiology
                Physiological Parameters
                Body Weight
                Body Mass Index
                Medicine and Health Sciences
                Physiology
                Physiological Parameters
                Body Weight
                Body Mass Index
                Research and Analysis Methods
                Mathematical and Statistical Techniques
                Statistical Methods
                Metaanalysis
                Physical Sciences
                Mathematics
                Statistics
                Statistical Methods
                Metaanalysis
                Biology and Life Sciences
                Computational Biology
                Genome Analysis
                Genome-Wide Association Studies
                Biology and Life Sciences
                Genetics
                Genomics
                Genome Analysis
                Genome-Wide Association Studies
                Biology and Life Sciences
                Genetics
                Human Genetics
                Genome-Wide Association Studies
                Biology and Life Sciences
                Physiology
                Physiological Parameters
                Body Weight
                Obesity
                Medicine and Health Sciences
                Physiology
                Physiological Parameters
                Body Weight
                Obesity
                Biology and Life Sciences
                Nutrition
                Diet
                Alcohol Consumption
                Medicine and Health Sciences
                Nutrition
                Diet
                Alcohol Consumption
                Medicine and Health Sciences
                Dermatology
                Skin Diseases
                Research and Analysis Methods
                Mathematical and Statistical Techniques
                Statistical Methods
                Instrumental Variable Analysis
                Physical Sciences
                Mathematics
                Statistics
                Statistical Methods
                Instrumental Variable Analysis
                Custom metadata
                The UK Biobank dataset used to conduct the research in this paper is available via application directly to the UK Biobank. Applications are assessed for meeting the required criteria for access, including legal and ethics standards. More information regarding data access can be found here: http://www.ukbiobank.ac.uk/scientists-3/. Data from the HUNT Study used in research projects will, when reasonably requested by others, be made available upon request to the HUNT Data Access Committee ( hunt@ 123456medisin.ntnu.no ). Data are only available to research groups with a PI affiliated with a Norwegian research institute. The HUNT data access information (available here: http://www.ntnu.edu/hunt/data) describes in detail the policy regarding data availability. BMI GWAS source data (Locke et al, 2015) are available from the GIANT consortium ( https://portals.broadinstitute.org/collaboration/giant/index.php/GIANT_consortium_data_files#GWAS_Anthropometric_2015_BMI). Psoriasis GWAS source data used in this study have been made available in S1 Appendix. This research has been conducted using data from the UK Biobank Resource (application numbers 10074 and 9072) and the Nord-Trøndelag Health Study (the HUNT Study).

                Medicine
                Medicine

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