Association between psoriatic disease and lifestyle factors and comorbidities: cross-sectional analysis and Mendelian randomization

Are psoriasis severity and comorbidities associated with diet quality? A cross-sectional analysis using UK Biobank

BACKGROUND & AIMS

Psoriasis has been linked to various diet-related comorbidities such as metabolic syndrome, type 2 diabetes, and cardiovascular disease. Evidence is lacking on the role of diet in the management of psoriasis and its comorbidities. We aimed to characterise the dietary patterns and quality of diet in individuals living with psoriasis and to assess whether psoriasis severity and comorbidities are associated with diet quality.

METHODS

Using the UK Biobank cohort, individuals identified with psoriasis via self-report and/or linked health records at baseline were compared with participants without psoriasis. Dietary intake was assessed through online 24 h-recalls (Oxford WebQ) conducted every 3-4 months over one year. Average nutrient and food group intakes were calculated from at least two 24 h dietary recalls to determine adherence to national food-based dietary guidelines (Eatwell Score (EWS), range: 0-9) and the Mediterranean-style diet (alternative Mediterranean diet (aMED) score, range: 0-9). Associations between psoriasis severity (using treatment category as a proxy), the presence of major comorbidities and diet quality scores were evaluated using regression models adjusting for covariates.

RESULTS

Among 2613 people with psoriasis (mean age 56.5, 49.6 % women) and 120,555 people without psoriasis (mean age 56.2, 56.2 % women), both groups had similar average scores for EWS (3.9 ± 1.7 for both groups). The psoriasis group had a slightly higher aMED score (4.4 ± 1.8 and 3.8 ± 1.7, P < 0.001). However, participants with psoriasis also reported higher intake of red and processed meat, sodium, free sugars, and alcohol (all P < 0.05) compared to the non-psoriasis group. Within the psoriasis group, no significant difference in diet quality was found between different clinical severities of psoriasis, but participants with the highest severity had lower odds of meeting guidelines for daily fruit and vegetable intakes (odds ratio (OR) 95 % confidence interval (CI): 0.69 (0.48, 0.98), P = 0.040) and scoring on nuts intake (OR (95 % CI): 0.66 (0.44, 1.00), P = 0.050) compared to those not receiving treatment. Participants in the psoriasis group with at least one comorbidity had significantly lower diet quality scores (EWS, beta (95%CI): -0.184 (-0.354, -0.014), P = 0.034; aMED beta (95%CI): -0.266 (-0.442, -0.089), P = 0.003).

CONCLUSIONS

Participants with psoriasis showed slightly better adherence to a Mediterranean-style diet but also consumed more processed meat, sodium, free sugars, and alcohol. Those with the most severe psoriasis or comorbidities had poorer diet quality, highlighting the opportunity for dietary interventions in this population.

Weighing in on obesity and psoriatic arthritis - Time to move beyond association to robust randomised trials

Almost one in two individuals with psoriatic arthritis (PsA) are now living with obesity. Obesity increases the risk of developing PsA, worsens disease activity, pain and fatigue, impairs treatment response, and amplifies the risk of many cardiometabolic comorbidities already more prevalent in PsA. Despite the increasing evidence for the pathogenic role of obesity in PsA, current treatment focuses on immune mediated therapies, with limited attention to tackling excess adiposity. Residual pain and disease activity in PsA can in turn adversely impact physical activity, leading to a cycle of further weight gain and worse disease activity. Preliminary evidence from dietary interventions in patients with PsA and obesity suggests weight loss of≥5% body weight can improve disease activity, holding promise for potentially even better improvements with newer pharmacological anti-obesity therapies, such as incretin-based weight loss medicines, which result in average weight losses of 15-20%. In this narrative review, we provide an overview of the adverse impacts of obesity in PsA and discuss weight loss therapies now available to help address this. We highlight the urgent need for robust randomised controlled trials of weight loss therapies in patients with PsA and obesity to determine their clinical and cost effectiveness in PsA management and to inform where these are best implemented in the disease course and treatment pathway.

Safety assessment of apremilast: real-world adverse event analysis from the FAERS database

Apremilast, a unique oral immunomodulatory phosphodiesterase 4 inhibitor, has been approved by the U.S. Food and Drug Administration (FDA) for the treatment of psoriasis and psoriatic arthritis (PsA). But there is a lack of real-world studies on the safety of apremilast in large numbers of people. This research employs the FAERS database to assess the real-world safety profile of apremilast to evaluate the association between apremilast and adverse events, which can guide drug monitoring and clinical practice. Our study collected adverse event reports listing apremilast as the primary suspect drug from the first quarter of 2012 to the first quarter of 2024. We utilized multiple disproportionality analysis methods, including reporting odds ratio (ROR), proportional reporting ratio (PRR), Bayesian confidence propagation neural network (BCPNN), and multi-item gamma Poisson shrinker (MGPS), to evaluate adverse events associated with apremilast. A comprehensive analysis yielded 124,734 reports identifying apremilast as the primary suspect drug, encompassing 252,677 preferred terms (PT) for adverse reactions distributed across 27 system organ class (SOC) categories. Apart from the adverse reactions already mentioned in the drug label, this study identified some new clinically valuable potential adverse reactions, such as vomiting, depression, suicidal ideation, weight decreased, decreased appetite, nasopharyngitis, dyspepsia, abdominal pain, gastrooesophageal reflux disease, abdominal distension, migraine, insomnia, memory impairment, muscle spasms, musculoskeletal stiffness and so on. Our study provide new safety information for the clinical use of apremilast and establish a framework and insights for its further safety evaluation.

Exploring the Link Between Genetic Predictors of Cardiovascular Disease and Psoriasis

Importance

The epidemiological link between immune-mediated diseases (IMIDs) and cardiovascular disease has often been attributed to systemic inflammation. However, the direction of causality and the biological mechanisms linking cardiovascular disease with IMIDs are incompletely understood. Given the robust epidemiological association and the growing body of supportive mechanistic evidence, psoriasis is an exemplary IMID model for exploring this relationship.

Objective

To assess the bidirectional relationships between genetic predictors of psoriasis and the 2 major forms of cardiovascular disease, coronary artery disease (CAD) and stroke, and to evaluate the association between genetic predictors of cardiovascular disease with 9 other IMIDs.

Design, Setting, and Participants

This was a genetic association study using mendelian randomization (MR), a powerful genetic tool to help distinguish causation from associations observed in epidemiological studies, to provide supportive evidence for causality between traits. The study conducted 2-sample MR analyses using summary-level data from large-scale genome-wide association meta-analysis studies (GWAS) for each trait. The analysis focused on individuals of European descent from GWAS meta-analyses, involving CAD, stroke, psoriasis, and 9 other IMIDs. Data were analyzed from January 2023 to May 2024.

Exposures

Genetic predictors of CAD, stroke, psoriasis, and 9 other IMIDs.

Main Outcomes and Measures

The primary outcomes were the associations of genetic predictors of CAD and stroke with the risk of psoriasis and 9 other IMIDs, determined using inverse-variance weighted (IVW) MR estimates.

Results

This study included 181 249 cases and 1 165 690 controls with CAD, 110 182 cases and 1 503 898 controls with stroke, 36 466 cases and 458 078 controls with psoriasis, for a total of approximately 3 400 000 individuals, and 9 other IMIDs. In contrast to previous assumptions, genetic predictors of psoriasis were found to have no association with CAD or stroke. In the reverse direction, genetic predictors of both CAD (MR estimate IVW odds ratio [OR], 1.07; 95% CI, 1.04-1.10; P = .003) and stroke (IVW OR, 1.22; 95% CI, 1.05-1.41; P = .01) were found to have risk-increasing associations with psoriasis. Adjusting for stroke rendered the associations of genetically predicted CAD with psoriasis risk nonsignificant (and vice versa), suggesting that a shared effect underlying genetic risk for CAD and stroke associates with increased psoriasis risk. No risk-increasing associations were observed for genetic predictors of cardiovascular disease with other common IMIDs, including rheumatoid arthritis and inflammatory bowel disease.

Conclusions and Relevance

Findings of this mendelian randomization study indicate that genetic predictors of cardiovascular disease were associated with increased psoriasis risk with no reciprocal effect or association with other IMIDs. Elucidating mechanisms underpinning this association could lead to novel therapeutic approaches in both diseases.

Genetically Proxied Interleukin-13 Inhibition Is Associated With Risk of Psoriatic Disease: A Mendelian Randomization Study

OBJECTIVE

Inhibitors of the interleukin 13 (IL-13) pathway, such as dupilumab, are licensed for atopic dermatitis and asthma. Adverse events resembling psoriatic disease after dupilumab initiation have been reported, but evidence is limited to case reports with uncertain causality. We aimed to investigate whether genetically mimicked IL-13 inhibition (IL-13i) is associated with risk of psoriatic arthritis (PsA) and psoriasis.

METHODS

We instrumented IL-13i using a protein-coding variant in the IL13 gene, rs20541, that is associated with circulating eosinophil count (biomarker of IL-13i) at genome-wide significance in a study of 563,946 individuals. Outcome genetic data were taken from studies of PsA, psoriasis, and related spondyloarthritis traits in up to 10,588 cases and 209,287 controls. Colocalization analysis was performed to examine genetic confounding. We additionally used circulating IgE as a biomarker to test whether associations were replicated, both in the test and in an independent genetic dataset. We also replicated analyses using individual-level data from the UK Biobank.

RESULTS

Genetically proxied IL-13i was associated with increased risk of PsA (odds ratio [OR] 37.39; 95% confidence interval [95% CI] 11.52-121.34; P = 1.64 × 10-9) and psoriasis (OR 20.08; 95% CI 4.38-92.01; P = 1.12 × 10-4). No consistent associations were found for Crohn disease, ulcerative colitis, ankylosing spondylitis, or iritis. Colocalization showed no strong evidence of genetic confounding for psoriatic disease. Results were replicated using circulating IgE for the exposure, using independent outcome data and using individual-level data.

CONCLUSION

We provide supportive genetic evidence that IL-13i is linked to increased risk of PsA and psoriasis. Physicians prescribing IL-13 inhibitors should be vigilant for these adverse events.

Adherence to general national dietary guidelines and risk of psoriasis: results from a general population study of 105 332 individuals

BACKGROUND

It is unknown if an unhealthy diet can affect the risk of developing psoriasis.

OBJECTIVES

To test the hypothesis that individuals with an unhealthy diet have an increased risk of prevalent and incident psoriasis.

METHODS

We included 105 332 adults from the Copenhagen General Population Study, who were invited to participate between 2003 and 2015. The response rate was 43%. An unhealthy vs. healthy diet was defined according to adherence to general national dietary guidelines. The participants were grouped into three groups: low, intermediate and high adherence to general national dietary guidelines; this was based on information from a food frequency questionnaire. Identification of psoriasis was made using International Classification of Diseases codes.

RESULTS

Of the 105 332 individuals, 580 had a diagnosis of psoriasis at the time of enrolment and 640 received a diagnosis during the median follow-up of 9 years. Risk of prevalent psoriasis increased according to nonadherence to general national dietary guidelines in a stepwise manner with an age- and sex-adjusted odds ratio of 1.70 (95% confidence interval 1.26-2.30) in individuals with low vs. high adherence to dietary guidelines. Results were similar in a multivariable-adjusted model. Prospective analyses adjusted for age and sex showed a weak association between nonadherence to dietary guidelines and risk of incident psoriasis (P for trend 0.04). This association disappeared, when adjusting for multiple confounders (P for trend 0.50).

CONCLUSIONS

Although individuals with psoriasis have an unhealthier diet, diet alone does not appear to independently increase the risk of developing psoriasis.

Targeting cytokines in psoriatic arthritis

Psoriatic arthritis (PsA) is part of the psoriatic disease spectrum and is characterized by a chronic inflammatory process that affects entheses, tendons and joints. Cytokines produced by immune and non-immune cells play a central role in the pathogenesis of PsA by orchestrating key aspects of the inflammatory response. Pro-inflammatory cytokines such as TNF, IL-23 and IL-17 have been shown to regulate the initiation and progression of PsA, ultimately leading to the destruction of the architecture of the local tissues such as soft tissue, cartilage and bone. The important role of cytokines in PsA has been underscored by the clinical success of antibodies that neutralize their function. In addition to biologic agents targeting individual pro-inflammatory cytokines, signaling inhibitors that block multiple cytokines simultaneously such as JAK inhibitors have been approved for PsA therapy. In this review, we will focus on our current understanding of the role of cytokines in the disease process of PsA and discuss potential new treatment options based on modulation of cytokine function.

Alcohol consumption and risk of psoriasis: Results from observational and genetic analyses in more than 100,000 individuals from the Danish general population

Background

Psoriasis is associated with high alcohol consumption, but the causality of this relationship is unclear.

Objective

We aimed to use a Mendelian randomization approach to investigate the causal effects of alcohol on incident psoriasis.

Methods

We included 102,655 adults from the prospective Copenhagen studies. All participants filled out a questionnaire on alcohol consumption, were physically examined, and had blood drawn for biochemical and genetic analyses. We created a genetic instrument based on the number of fast-metabolizing alleles in alcohol dehydrogenase 1B and alcohol dehydrogenase 1C, known to be associated with alcohol consumption, to test whether alcohol consumption was causally associated with psoriasis.

Results

Observationally, we found an increased risk of incident psoriasis among individuals with high alcohol consumption compared to those with low alcohol consumption with a hazard ratio of 1.30 (95% confidence interval 1.05-1.60) in the fully adjusted model. Using genetic data to predict alcohol consumption to avoid confounding and reverse causation, we found no association between number of fast-metabolizing alleles and risk of psoriasis.

Limitations

Alcohol consumption was self-reported and psoriasis was defined using the International Classification of Diseases 10th revision and 8th revision codes.

Conclusion

Alcohol consumption is observationally but not causally associated with incident psoriasis.

Multiple long-term conditions in people with psoriasis: a latent class and bidirectional Mendelian randomization analysis

BACKGROUND

Coexisting long-term conditions (LTCs) in psoriasis and their potential causal associations with the disease are not well -established.

OBJECTIVES

To determine distinct clusters of LTCs in people with psoriasis and the potential bidirectional causal association between these LTCs and psoriasis.

METHODS

Using latent class analysis, cross-sectional data from people with psoriasis from the UK Biobank were analysed to identify distinct psoriasis-related comorbidity profiles. Linkage disequilibrium score regression (LDSR) was applied to compute the genetic correlation between psoriasis and LTCs. Two-sample bidirectional Mendelian randomization (MR) analysis assessed the potential causal direction using independent genetic variants that reached genome-wide significance (P < 5 × 10-8).

RESULTS

Five comorbidity clusters were identified in a population of 10 873 people with psoriasis. LDSR revealed that psoriasis was positively genetically correlated with heart failure [genetic correlation (rg) = 0.23, P = 8.8 × 10-8], depression (rg = 0.12, P = 2.7 × 10-5), coronary artery disease (CAD; rg = 0.15, P = 2 × 10-4) and type 2 diabetes (rg = 0.19, P = 3 × 10-3). Genetic liability to CAD was associated with an increased risk of psoriasis [inverse variance weighted (IVW) odds ratio (ORIVW) 1.159, 95% confidence interval (CI) 1.055-1.274; P = 2 × 10-3]. The MR pleiotropy residual sum and outlier (MR-PRESSO; ORMR-PRESSO 1.13, 95% CI 1.042-1.228; P = 6 × 10-3) and the MR-robust adjusted profile score (RAPS) (ORMR-RAPS 1.149, 95% CI 1.062-1.242; P = 5 × 10-4) approaches corroborate the IVW findings. The weighted median (WM) generated similar and consistent effect estimates but was not statistically significant (ORWM 1.076, 95% CI 0.949-1.221; P = 0.25). Evidence for a suggestive increased risk was detected for CAD (ORIVW 1.031, 95% CI 1.003-1.059; P = 0.03) and heart failure (ORIVW 1.019, 95% CI 1.005-1.033; P = 9 × 10-3) in those with a genetic liability to psoriasis; however, MR sensitivity analyses did not reach statistical significance.

CONCLUSIONS

Five distinct clusters of psoriasis comorbidities were observed with these findings to offer opportunities for an integrated approach to comorbidity prevention and treatment. Coexisting LTCs share with psoriasis common genetic and nongenetic risk factors, and aggressive lifestyle modification in these people is anticipated to have an impact beyond psoriasis risk. Genetically predicted CAD is possibly associated with an increased risk of psoriasis, altering our prior knowledge.

Associations of polysocial risk score, lifestyle and genetic factors with incident psoriasis: a larger-scale prospective cohort study

OBJECTIVES

The impact of polysocial risk score (PsRS), a composite measure of multiple social risk factors, on the development of psoriasis remains unclear. Moreover, the potential modifying effects of lifestyle and genetic susceptibility on the relationship between PsRS and psoriasis risk require further exploration.

STUDY DESIGN

This was a prospective cohort study conducted among UK Biobank.

METHODS

In this study, we analyzed 331,631 participants enrolled in the UK Biobank cohort. To derive the PsRS, we utilized a summative strategy, amalgamating six social determinants of health derived from three domains: socio-economic status, psychosocial factors, and neighborhood and living environment consistently linked to incident psoriasis. Cox proportional hazard models were used to assess the associations between PsRS and psoriasis incidence. Furthermore, we constructed a lifestyle score and a genetic risk score to explore the potential modifying effects of these factors on the relationship between PsRS and psoriasis risk.

RESULTS

Compared with individuals with a low PsRS (≤1), those with intermediate PsRS (2-4) and high PsRS (≥5) had 1.20 (95% confidence interval [CI], 1.06-1.36) and 1.53 (95% CI, 1.31-1.78) times higher risks of developing psoriasis, respectively. Our findings revealed an additive interaction between PsRS and genetic susceptibility. Moreover, it was found that individuals with high PsRS and unhealthier lifestyles had a 2.60 times higher risk of developing psoriasis than those with lower PsRS and healthier ones.

CONCLUSIONS

Our study results imply that an elevated PsRS is linked to a heightened risk of psoriasis, which is further influenced by genetic factors. Our results also indicate that greater social vulnerability and unhealthier lifestyle may synergistically contribute to the additional risk of psoriasis.

The impact of dietary interventions in psoriatic arthritis

PURPOSE OF REVIEW

Psoriatic arthritis (PsA) is a common form of inflammatory arthritis that affects people with psoriasis. Both psoriasis and PsA are associated with metabolic diseases including obesity, hypertension, hyperlipidaemia, diabetes mellitus, fatty liver disease, and cardiovascular disease including myocardial infarction. Dietary interventions for psoriatic disease have been of great interest, particularly among patients with PsA.

RECENT FINDINGS

Herein, we review the evidence for dietary intervention in psoriatic arthritis. To date, weight loss among patients who are obese has the greatest evidence for benefit. We also examine the evidence for fasting, nutrient supplementation, and specific diets as adjunct therapeutic strategies.

SUMMARY

While the data do not clearly support a single dietary intervention across the disease, weight loss among those who are obese results in improved PsA disease activity and physical function. Additional studies are needed to better understand the impact of diet on psoriatic arthritis.

The Association of Psoriasis, Diabetes Mellitus, and Hypertension: A Meta-Analysis

Psoriasis is a systemic disease affecting various organs; however, it is usually thought of as a skin disease. A multidisciplinary approach is needed for better outcomes. The current meta-analysis assessed the association between diabetes mellitus, high blood pressure, and psoriasis. We searched four databases, including Cochrane Library, PubMed, MEDLINE, and Google Scholar, for relevant articles using the following keywords: psoriasis, hypertension, high blood pressure, cardiovascular risk factors, and diabetes mellitus. The author's name, year, and country of publication, diabetes, and hypertension among patients with psoriasis and control subjects were collected and entered into a Microsoft Excel sheet. Out of 1209 articles retrieved, 903 articles remained after duplication removal. From the 82 full texts screened, only seven studies fulfilled the inclusion and exclusion criteria. Psoriasis was associated with diabetes and hypertension: odds ratio 1.38, 95% CI 1.17-1.64; P-value 0.0002, chi-square 224.93, and odds ratio 1.60, 95% CI 1.41-1.81, P-value 0.00001, chi-square 226.59, respectively. Substantial heterogeneity was observed (I2 for heterogeneity, 97%, P < 0.001). A broad approach is needed to address the associated comorbidities and select the appropriate therapeutic approach. Randomized controlled trials investigating the best drugs for the treatment of psoriasis and its associated cardiovascular risk factors are needed.

Genetic causal relationship between gut microbiome and psoriatic arthritis: a bidirectional two-sample Mendelian randomization study

Background

Several observational studies have suggested a potential relationship between gut microbiome and psoriatic arthritis (PsA). However, the causality of this relationship still remains unclear. We aim to explore if the specific gut microbiome is causally associated with PsA at the genetic level and offer valuable insights into the etiology of PsA.

Methods

In this study, we employed a bidirectional two-sample Mendelian randomization (MR) analysis to investigate the causal effects of the gut microbiome on PsA. Publicly accessible genome-wide association study summary data of gut microbiome were obtained from the MiBioGen consortium (n = 14,306), while the summary statistics of psoriatic arthropathies were sourced from the FinnGen consortium R8 release data (2,776 cases and 221,323 controls). The primary analytical method employed was inverse variance weighted (IVW), complemented by supplementary methods including MR-Egger, weighted median, weighted mode, maximum likelihood, MR-PRESSO, and cML-MA. Reverse MR analysis was performed on the bacteria that were found to be causally associated with PsA in forward MR analysis. Cochran's IVW Q statistic was utilized to assess the heterogeneity of instrumental variables among the selected single nucleotide polymorphisms.

Results

IVW estimates revealed that Ruminococcaceae_UCG-002 (odds ratio (OR) = 0.792, 95% confidence interval (CI), 0.643-0.977, p = 0.029) exhibited a protective effect on PsA. Conversely, Blautia (OR = 1.362, 95% CI, 1.008-1.842, p = 0.044), Eubacterium_fissicatena_group (OR = 1.28, 95% CI, 1.075-1.524, p = 0.006), and Methanobrevibacter (OR = 1.31, 95% CI, 1.059-1.621, p = 0.013) showed a positive correlation with the risk of PsA. No significant heterogeneity, horizontal pleiotropy, or outliers were observed, and the results of the MR analysis remained unaffected by any single nucleotide polymorphisms. According to the results of reverse MR analysis, no significant causal effect of PsA was found on gut microbiome.

Conclusion

This study establishes for the first time a causal relationship between the gut microbiome and PsA, providing potential valuable strategies for the prevention and treatment of PsA. Further randomized controlled trials are urgently warranted to support the targeted protective mechanisms of probiotics on PsA.

Association of Lipid-Lowering Drugs With Risk of Psoriasis: A Mendelian Randomization Study

Importance

Lipid pathways have been implicated in the pathogenesis of psoriasis, and some lipid-lowering drugs, such as statins, are hypothesized to have disease-modifying properties. However, large population-level studies are scarce, and causal interpretation of results from traditional observational designs is limited by confounding.

Objective

To investigate the causal association between genetically proxied lipid-lowering drugs and psoriasis risk.

Design, Setting, and Participants

This 2-sample mendelian randomization study was performed from August to October 2022 and included population-level genome-wide association studies of psoriasis in the UK Biobank and FinnGen studies and low-density lipoprotein (LDL) by the Global Lipids Genetics Consortium. The inverse variance-weighted method was used with pleiotropy robust methods and colocalization as sensitivity analyses.

Exposures

Genetically proxied inhibition of 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR, targeted by statins), Niemann-Pick C1-like 1 (NPC1L1, targeted by ezetimibe), and proprotein convertase subtilisin/kexin type 9 (PCSK9, targeted by, eg, alirocumab), using LDL as the biomarker.

Main Outcomes and Measures

Risk of psoriasis.

Results

Data from 12 116 patients with psoriasis and approximately 1.3 million individuals with LDL measurement were analyzed. Genetically proxied PCSK9 inhibition was associated with reduced risk of psoriasis (odds ratio, 0.69 per standard deviation reduction in LDL; 95% CI, 0.55-0.88; P = .003), which was replicated in FinnGen (odds ratio, 0.71; 95% CI, 0.57-0.88; P = .002). Sensitivity analyses did not provide statistical evidence of bias from pleiotropy or genetic confounding. No robust association was found for HMGCR or NPC1L1 inhibition.

Conclusions and Relevance

This mendelian randomization study suggests that PCSK9 is implicated in psoriasis pathogenesis, and its inhibition is associated with reduced psoriasis risk. These findings potentially pave the way for future studies that may allow personalized selection of lipid-lowering drugs for those at risk of psoriasis.

Smoking is an independent but not a causal risk factor for moderate to severe psoriasis: A Mendelian randomization study of 105,912 individuals

Background

Smoking is strongly associated with higher risk of psoriasis in several observational studies; however, whether this association is causal or can be explained by confounding or reverse causation is not fully understood. Randomized controlled trials are the gold standard when examining causality; however, when this method is not feasible, the Mendelian randomization design is an alternative. Herein genetic variants can be used as robust proxies for modifiable exposures and thereby avoiding confounding and reverse causation.In this study, we hypothesized that smoking is an independent and causal risk factor for psoriasis and tested this using a Mendelian randomization design.

Methods

We used data from the Copenhagen General Population Study including 105,912 individuals with full information on lifestyle factors, biochemistry, and genotype data. In total, 1,240 cases of moderate to severe psoriasis were included to investigate the association between smoking and psoriasis. To assess causality of the association, we used the genetic variant CHRNA3 rs1051730, where the T-allele is strongly associated with high lifelong cumulative smoking, as a proxy for smoking.

Results

In observational analyses, the multivariable adjusted hazard ratio of developing moderate to severe psoriasis was 1.64 (95% confidence interval: 1.35-2.00) in ever smokers with ≤ 20 pack-years and 2.23 (1.82-2.73) in ever smokers with > 20 pack-years compared to never smokers. In genetic analyses, the odds ratio of developing moderate to severe psoriasis was 1.05 (0.95-1.16) per CHRNA3 rs10511730 T-allele in ever smokers.

Conclusion

Smoking was an independent risk factor for moderate to severe psoriasis in observational analyses. However, using a genetic variant as a robust proxy for smoking, we did not find this association to be causal.

Non-alcoholic fatty liver disease is not a causal risk factor for psoriasis: A Mendelian randomization study of 108,835 individuals

Background

Psoriasis is observationally associated with a higher risk of non-alcoholic fatty liver disease (NAFLD); however, the causal relationship between the two diseases remains unclear.

Objective

We hypothesized that individuals with NAFLD or elevated liver fat content have higher risk of psoriasis and that NAFLD is a causal risk factor for psoriasis. We tested this using a Mendelian randomization approach.

Methods

We included 108,835 individuals from the Danish general population, including 1,277 individuals with psoriasis and 802 individuals with NAFLD according to ICD codes. To estimate liver fat content, a subset of the participants (N = 7,416) also had a CT scan performed. First, we tested whether a diagnosis of NAFLD or elevated liver fat content was observationally associated with risk of psoriasis. Subsequently, we used the genetic variants PNPLA3 and TM6SF2, both strongly associated with NAFLD and high liver fat content, to test whether NAFLD was causally associated with increased risk of psoriasis.

Results

Observationally, individuals with vs. without a diagnosis of NAFLD had higher risk of psoriasis with an odds ratio of 2.03 (95% confidence interval 1.28-3.21). The risk of psoriasis increased in a stepwise manner with increasing liver fat content with an odds ratio of 5.00 (2.63-9.46) in individuals in the highest quartile of liver fat content compared to individuals in the lowest quartile. In genetic analyses, PNPLA3 and TM6SF2 were both associated with increased risk of NAFLD but not with increased risk of psoriasis.

Conclusion

Observationally, a diagnosis of NAFLD or elevated liver fat content was associated with higher risk of psoriasis. However, using genetic variants as a proxy for NAFLD, we did not find evidence of a causal relationship between NAFLD and psoriasis. Thus, the observational association between NAFLD and psoriasis is presumably a result of shared confounding factors or reverse causation.