Alcohol intake and risk of rheumatoid arthritis: a Mendelian randomization study

The Causal Association between Alcohol, Smoking, Coffee Consumption, and the Risk of Arthritis: A Meta-Analysis of Mendelian Randomization Studies

Objective: To evaluate the genetic causality between alcohol intake, smoking, coffee consumption, and arthritis. Methods: Mendelian randomization (MR) studies with alcohol, smoking, and coffee consumption behaviors as exposures, and osteoarthritis (OA) and rheumatoid arthritis (RA) as outcomes were retrieved from up to July 2023. Two researchers with relevant professional backgrounds independently assessed the quality and extracted data from the included studies. Meanwhile, we applied MR analyses of four lifestyle exposures and five arthritis outcomes (two for OA and three for RA) with gene-wide association study (GWAS) data that were different from the included studies, and the results were also included in the meta-analysis. Statistical analyses were performed using Stata 16.0 and R software version 4.3.1. Results: A total of 84 studies were assessed. Of these, 11 were selected for meta-analysis. As a whole, the included studies were considered to be at a low risk of bias and were of high quality. Results of the meta-analysis showed no significant genetic causality between alcohol intake and arthritis (odds ratio (OR): 1.02 (0.94-1.11)). Smoking and arthritis had a positive genetic causal association (OR: 1.44 (1.27-1.64)) with both OA (1.44 (1.22-1.71)) and RA (1.37 (1.26-1.50)). Coffee consumption and arthritis also had a positive genetic causal association (OR: 1.02 (1.01-1.03)). Results from the subgroup analysis showed a positive genetic causality between coffee consumption and both OA (OR: 1.02 (1.00-1.03)) and RA (OR: 1.56 (1.19-2.05)). Conclusion: There is positive genetic causality between smoking and coffee consumption and arthritis (OA and RA), while there is insufficient evidence for genetic causality between alcohol intake and arthritis.

Appraising causal risk and protective factors for rheumatoid arthritis

Aims

Mendelian randomization (MR) is considered to overcome the bias of observational studies, but there is no current meta-analysis of MR studies on rheumatoid arthritis (RA). The purpose of this study was to summarize the relationship between potential pathogenic factors and RA risk based on existing MR studies.

Methods

PubMed, Web of Science, and Embase were searched for MR studies on influencing factors in relation to RA up to October 2022. Meta-analyses of MR studies assessing correlations between various potential pathogenic factors and RA were conducted. Random-effect and fixed-effect models were used to synthesize the odds ratios of various pathogenic factors and RA. The quality of the study was assessed using the Strengthening the Reporting of Observational Studies in Epidemiology using Mendelian Randomization (STROBE-MR) guidelines.

Results

A total of 517 potentially relevant articles were screened, 35 studies were included in the systematic review, and 19 studies were eligible to be included in the meta-analysis. Pooled estimates of 19 included studies (causality between 15 different risk factors and RA) revealed that obesity, smoking, coffee intake, lower education attainment, and Graves' disease (GD) were related to the increased risk of RA. In contrast, the causality contribution from serum mineral levels (calcium, iron, copper, zinc, magnesium, selenium), alcohol intake, and chronic periodontitis to RA is not significant.

Conclusion

Obesity, smoking, education attainment, and GD have real causal effects on the occurrence and development of RA. These results may provide insights into the genetic susceptibility and potential biological pathways of RA.

Falsification of the instrumental variable conditions in Mendelian randomization studies in the UK Biobank

Mendelian randomization (MR) is an increasingly popular approach to estimating causal effects. Although the assumptions underlying MR cannot be verified, they imply certain constraints, the instrumental inequalities, which can be used to falsify the MR conditions. However, the instrumental inequalities are rarely applied in MR. We aimed to explore whether the instrumental inequalities could detect violations of the MR conditions in case studies analyzing the effect of commonly studied exposures on coronary artery disease risk.Using 1077 single nucleotide polymorphisms (SNPs), we applied the instrumental inequalities to MR models for the effects of vitamin D concentration, alcohol consumption, C-reactive protein (CRP), triglycerides, high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol on coronary artery disease in the UK Biobank. For their relevant exposure, we applied the instrumental inequalities to MR models proposing each SNP as an instrument individually, and to MR models proposing unweighted allele scores as an instrument. We did not identify any violations of the MR assumptions when proposing each SNP as an instrument individually. When proposing allele scores as instruments, we detected violations of the MR assumptions for 5 of 6 exposures.Within our setting, this suggests the instrumental inequalities can be useful for identifying violations of the MR conditions when proposing multiple SNPs as instruments, but may be less useful in determining which SNPs are not instruments. This work demonstrates how incorporating the instrumental inequalities into MR analyses can help researchers to identify and mitigate potential bias.

Testing relationship between tea intake and the risk of rheumatoid arthritis and systemic lupus erythematosus: a Mendelian randomization study

BACKGROUND

We performed Mendelian randomization (MR) to assess the causal effect of tea intake on rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE).

METHODS

Genetic instruments for tea intake were obtained from a large genome-wide association study (GWAS) dataset of the UK Biobank. Genetic association estimates for RA (6236 cases and 147,221 controls) and SLE (538 cases and 213,145 controls) were obtained from the FinnGen study through the IEU GWAS database.

RESULTS

MR analyses using the inverse-variance weighted method showed that tea intake was not associated with risk of RA [odds ratio (OR) per standard deviation increment in genetically predicted tea intake = 0.997, 95% confidence interval (CI) 0.658-1.511] and SLE (OR per standard deviation increment in genetically predicted tea intake = 0.961, 95% CI 0.299-3.092). Weighted median, weighted mode, MR-Egger, leave-one-out and multivariable MR controlling for several confounding factors including current tobacco smoking, coffee intake, and alcoholic drinks per week yielded completely consistent results. No evidence of heterogeneity and pleiotropy was found.

CONCLUSION

Our MR study did not suggest a causal effect of genetically predicted tea intake on RA and SLE.

Robust anti-inflammatory activity of genistein against neutrophil elastase: a microsecond molecular dynamics simulation study

Human Neutrophil Elastase (HNE) is one of the major causes of tissue destruction in numerous chronic and inflammatory disorders and has been reported as a therapeutic target for inflammatory diseases. Overexpression of this enzyme plays a critical role in the pathogenesis of rheumatoid arthritis (RA). The focus of this study is to identify potent natural inhibitors that could target the active site of the HNE through the use of computational methods. The molecular structure of small molecules was retrieved from several natural compound databases. This was followed by structure-based virtual screening, molecular docking, ADMET property predictions and molecular dynamic simulation studies to screen potential HNE inhibitors. In total, 1881 natural compounds were extracted and subjected to molecular docking studies, and 10 compounds were found to have good interactions, exhibiting the best docking scores. Genistein showed higher binding efficacy (-10.28 Kcal/mol) to HNE in comparison to other natural compounds. The conformational stability of the docked complex of the ELANE gene (HNE) with genistein was assessed using 1-microsecond molecular dynamic simulation (MDs), which reliably revealed the unique stereochemical alteration of the complex, indicating its conformational stability and flexibility. Alterations in the enzyme structure upon complex formation were further characterized through clustering analysis and linear interaction energy (LIE) calculation. The outcomes of this research propose novel potential candidates against target HNE.Communicated by Ramaswamy H. Sarma.

Associations of rheumatoid arthritis and rheumatoid factor with mental health, sleep and cognition characteristics in the UK Biobank

While previous rheumatoid arthritis (RA) studies have focussed on cardiometabolic and lifestyle factors, less research has focussed on psychological variables including mood and cognitive health, and sleep. Cross-sectional analyses tested for associations between RA and RF+ (positive rheumatoid factor) vs. mental health (depression, anxiety, neuroticism), sleep variables and cognition scores in UK Biobank (total n = 484,064). Those RF+ were more likely to report longer sleep duration (β = 0.01, SE = 0.004, p < 0.01) and less likely to get up in the morning easily (OR 0.95, 95% CI 0.92-0.99, p = 0.01). Those reporting RA were more likely to score higher for neuroticism (β = 0.05, SE = 0.01, p < 0.001), to nap during the day (OR 1.10, 95% CI 1.06-1.14, p < 0.001), have insomnia (OR 1.28, 95% CI 1.22-1.35, p < 0.001), have slower reaction times (β = 0.02, SE = 0.008, p < 0.005) and score less for fluid intelligence (β = - 0.03, SE = 0.01, p < 0.05) and less likely to get up easily (OR 0.61, 95% CI 0.58-0.64, p < 0.001). The current study suggests that prevalent RA, and RF+ status are associated with differences in mental health, sleep, and cognition, highlighting the importance of addressing these aspects in clinical settings and future research.

A Roadmap for Investigating Preclinical Autoimmunity Using Patient-Oriented and Epidemiologic Study Designs: Example of Rheumatoid Arthritis

Background & Aims

Rheumatoid arthritis (RA) is a prototypic autoimmune disease causing inflammatory polyarthritis that affects nearly 1% of the population. RA can lead to joint destruction and disability along with increased morbidity and mortality. Similar to other autoimmune diseases, RA has distinct preclinical phases corresponding to genetic risk, lifestyle risk factors, autoantibody development, and non-specific symptoms prior to clinical diagnosis. This narrative review will detail observational studies for RA risk and clinical trials for RA prevention as a roadmap to investigating preclinical autoimmunity that could be applied to other diseases.

Methods

In this narrative review, we summarized previous and ongoing research studies investigating RA risk and prevention, categorizing them related to their design and preclinical phases.

Results

We detailed the following types of studies investigating RA risk and prevention: retrospective population-based and administrative datasets; prospective studies (case-control and cohort; some enrolling based on genetics, first-degree relative status, elevated biomarkers, or early symptoms/arthritis); and randomized clinical trials. These correspond to all preclinical RA phases (genetic, lifestyle, autoimmunity, early signs/symptoms). Previous and ongoing randomized controlled trials have enrolled individuals at very elevated risk for RA based on biomarkers, symptoms, imaging abnormalities, or early signs/symptoms.

Conclusion

We detailed the rich variety of study designs that is necessary to investigate distinct preclinical phases of an autoimmune disease such as RA. However, further progress is needed to fully elucidate the pathogenesis of RA that may ultimately lead to prevention or delay of disease onset.

No Causal Association Between Adiponectin and the Risk of Rheumatoid Arthritis: A Mendelian Randomization Study

Background: Accumulating evidence from observational studies suggested that circulating adiponectin levels are associated with the risk of rheumatoid arthritis (RA), but the causality remains unknown. We aimed to assess the causal relationship of adiponectin with RA risk. Methods: Based on summary statistics from large-scale genome-wide association studies (GWAS), we quantified the genetic correlation between adiponectin and RA. Then bidirectional Mendelian randomization (MR) analysis was performed to assess the causal relationship. Twenty single-nucleotide polymorphisms (SNPs) associated with adiponectin were selected as instrumental variables from a recent GWAS (n = 67,739). We applied theses SNPs to a large-scale GWAS for RA (14,361 cases and 43,923 controls) with replication using RA data from the FinnGen consortium (6,236 cases and 147,221 controls) and the UK Biobank (5,201 cases and 457,732 controls). The inverse-variance weighted (IVW) and multiple pleiotropy-robust methods were used for two-sample MR analyses. Results: Our analyses showed no significant genetic correlation between circulating adiponectin levels and RA [rG = 0.127, 95% confidence interval (CI): -0.012 to 0.266, P = 0.074]. In MR analyses, genetically predicted adiponectin levels were not significantly associated with the RA risk (odds ratio: 0.98, 95% CI: 0.88-1.09, P = 0.669). In the reverse direction analysis, there is little evidence supporting an association of genetic susceptibility to RA with adiponectin (β: 0.007, 95% CI: -0.003 to 0.018, P = 0.177). Replication analyses and sensitivity analyses using different models yielded consistent results. Conclusions: Our findings provided no evidence to support the causal effect of adiponectin levels on RA risk and of RA on circulating adiponectin levels.

Causal risk and protective factors in rheumatoid arthritis: A genetic update

The characterization of risk and protective factors in complex diseases such as rheumatoid arthritis (RA) has evolved from epidemiological studies, which test association, to the use of Mendelian randomization approaches, which test direct relationships. Indeed, direct associations with the mucosal origin of RA are retrieved with periodontal disease (Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans predominantly), interstitial lung involvement, tobacco smoking and air pollutants. Next, factors directly associated with an acquired immune response include genetic factors (HLA DRB1, PTPN22), capacity to produce anti-modified protein antibodies (AMPA), and relatives with a history of autoimmune diseases. Finally, factors can be also classified according to their direct capacity to interfere with the IL-6/CRP/sIL-IL6R proinflammatory pathway as risk factor (body fat, cardiometabolic factors, type 2 diabetes, depressive syndrome) or either as protective factors by controlling of sIL-6R levels (higher education level, and intelligence). Although some co-founders have been characterized (e.g. vitamin D, physical activity, cancer) the direct association with sex-discrepancy, pregnancy, and infections among other factors remains to be better explored.

The effects of alcohol consumption and its associations with disease activity among 979 patients with inflammatory arthritis

Objective

The role of alcohol in inflammatory disease remains debated. This study explores the relationship between alcohol and disease activity in patients with inflammatory arthritis.

Methods

Patients attending a rheumatology clinic between 2010 and 2020 were prospectively followed. Information on demographics, alcohol use, smoking habits and disease outcome measures were collected from these patients. Statistical analysis included univariate and multivariate linear and binary logistic regressions, Mann-Whitney U tests and one-way analysis of variance with Tukey’s honest significant difference (HSD) test.

Results

Of the 979 analysed patients, 62% had rheumatoid arthritis (RA), 26.7% had psoriatic arthritis (PsA) and 11.2% had ankylosing spondylitis. Mean DAS28-CRP (Disease Activity Score 28 - C-reactive protein) in RA and PsA at 1 year was 2.96±1.39, and 64.2% of patients were in remission (DAS28-CRP ≤2.6 or BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) ≤4). Both male gender and risky drinking (>15 units of weekly alcohol) were significantly associated with remission. Compared with women, men had an OR of 1.8 (1.1, 2.5) (p=0.034) for any alcohol consumption and 6.9 (4.7, 9.1) (p=0.001) for drinking at least 15 weekly drinks. When adjusted for gender, there was no association between alcohol and disease activity. Yet, when adjusted for alcohol consumption, gender still significantly influenced disease activity.

Conclusion

While it may appear that alcohol is linked to remission in inflammatory arthritis, when adjusted for gender, it is not. Men with inflammatory arthritis drink significantly more than women and have less severe disease activity.

Alcohol Consumption and Risk of Rheumatoid Arthritis among Chinese Adults: A Prospective Study

Alcohol consumption may be associated with the risk of rheumatoid arthritis (RA), but potential sex-related differences in this association have not been explored. Thus, we utilized 87,118 participants in the Kailuan Study, a prospective cohort initiated in 2006 to study the risk factors of cardiovascular disease in a Chinese population. We included those that did not have RA at baseline (2006), and performed cox proportional hazard modeling to calculate the hazard ratio (HR) and 95% confidence interval (95% CI) of RA according to the levels of alcohol consumption (never or past, light or moderate (<1 serving/day for women, <2 servings/day for men), and heavy (>1 serving/day for women, >2 servings/day for men), adjusting for age, sex, body mass index, and smoking. Diagnoses of RA were confirmed via medical record review by rheumatologists. From 2006 to 2018, we identified 87 incident RA cases. After adjusting for potential confounders, the HR of RA was 1.26 (95% CI: 0.62, 2.56) for participants with light or moderate alcohol consumption and 1.98 (95% CI: 0.93, 4.22) for participants with heavy alcohol consumption) versus non-drinkers. The HR of each 10 g increase in alcohol consumption was 1.11 (95% CI: 0.98, 1.26) (p-trend = 0.09). A significant association between alcohol consumption and RA risk was observed in women, but not in men (p for interaction = 0.06). Among women, each 10 g increase in alcohol consumption was significantly associated with a high risk of RA (HR: 1.56; 95% CI: 1.06, 2.29). In contrast, each 10 g increase in alcohol consumption was not significantly associated with the risk of RA in men (HR: 1.10; 95% CI: 0.97, 1.25). Excluding past drinkers generated similar results. In this prospective Chinese cohort, increasing alcohol consumption was associated with an elevated risk of RA among women, but not in men. These findings highlight the importance of incorporating analysis of sex differences into future studies of alcohol consumption and RA risk.

Alcohol Consumption and Risk of Common Autoimmune Inflammatory Diseases-Evidence From a Large-Scale Genetic Analysis Totaling 1 Million Individuals

Purpose: Observational studies have suggested a protective effect of alcohol intake with autoimmune disorders, which was not supported by Mendelian randomization (MR) analyses that used only a few (<20) instrumental variables.

Methods: We systemically interrogated a putative causal relationship between alcohol consumption and four common autoimmune disorders, using summary-level data from the largest genome-wide association study (GWAS) conducted on inflammatory bowel disease (IBD), rheumatoid arthritis (RA), multiple sclerosis (MS), and systemic lupus erythematosus (SLE). We quantified the genetic correlation to examine a shared genetic similarity. We constructed a strong instrument using 99 genetic variants associated with drinks per week and applied several two-sample MR methods. We additionally incorporated excessive drinking as reflected by alcohol use disorder identification test score.

Results: We observed a negatively shared genetic basis between alcohol intake and autoimmune disorders, although none was significant (r_g = −0.07 to −0.02). For most disorders, genetically predicted alcohol consumption was associated with a slightly (10–25%) decreased risk of onset, yet these associations were not significant. Meta-analyzing across RA, MS, and IBD, the three Th1-related disorders yielded to a marginally significantly reduced effect [OR = 0.70 (0.51–0.95), P = 0.02]. Excessive drinking did not appear to reduce the risk of autoimmune disorders.

Conclusions: With its greatly augmented sample size and substantially improved statistical power, our MR study does not convincingly support a beneficial role of alcohol consumption in each individual autoimmune disorder. Future studies may be designed to replicate our findings and to understand a causal effect on disease prognosis.

Network Meta-Analysis on the Mechanisms Underlying Alcohol Augmentation of COVID-19 Pathologies

Background

The coronavirus disease 2019 (COVID‐19) pandemic is a worldwide crisis caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). Many COVID‐19 patients present with fever in the early phase, with some progressing to a hyperinflammatory phase. Ethanol (EtOH) exposure may lead to systemic inflammation. Network meta‐analysis was conducted to examine possible relationships between EtOH consumption and COVID‐19 pathologies.

Methods

Molecules affected by EtOH exposure were identified by analysis with QIAGEN Knowledge Base. Molecules affected by COVID‐19 were identified from studies in MEDLINE, bioRxiv, and medRxiv reporting gene expression profiles in COVID‐19 patients, QIAGEN Coronavirus Network Explorer, and analysis of the RNA‐sequencing data of autopsied lungs of COVID‐19 patients retrieved from the GEO database. Network meta‐analysis was then conducted on these molecules using QIAGEN Ingenuity Pathway Analysis (IPA).

Results

Twenty‐eight studies reporting significant gene expression changes in COVID‐19 patients were identified. One RNA‐sequencing dataset on autopsied lungs of COVID‐19 patients was retrieved from GEO. Our network meta‐analysis suggests that EtOH exposure may augment the effects of SARS‐CoV‐2 infection on hepatic fibrosis signaling pathway, cellular metabolism and homeostasis, inflammation, and neuroinflammation. EtOH may also enhance the activity of key mediators including cytokines, such as IL‐1β, IL‐6, and TNF, and transcription factors, such as JUN and STAT, while inhibiting the activity of anti‐inflammatory mediators including glucocorticoid receptor. Furthermore, IL‐1β, IL‐6, TNF, JUN, and STAT were mapped to 10 pathways predicted to associate with SARS‐CoV‐2 proteins, including HMGB1, IL‐1, and IL‐6 signaling pathways.

Conclusions

Our meta‐analyses demonstrate that EtOH exposure may augment SARS‐CoV‐2–induced inflammation by altering the activity of key inflammatory mediators. Our findings suggest that it is important for clinicians to caution patients about the risk of alcohol consumption, which has increased during the COVID‐19 pandemic. The findings also call for further investigation into how alcohol exposure affects viral infections.

Long-term methotrexate use in rheumatoid arthritis patients: real-world data from the MARTE study

BACKGROUND

The MARTE study investigated the demographic, clinical, and therapeutic characteristics of rheumatoid arthritis (RA) patients ongoing methotrexate (MTX) treatment for longer than 8 years.

METHODS

This cross-sectional, observational study considered 587 RA patients from 67 Rheumatology Units across Italy. Data collected included demographic, clinical, and therapeutic characteristics, focusing on MTX prescription patterns (route of administration, dosing regimens, treatment duration, and discontinuation).

RESULTS

As initial therapy, 90.6% of patients received one conventional synthetic Disease Modifying Anti Rheumatic Drug (csDMARD), with treatment started within the first 3 months from diagnosis in half of the patients. MTX was the first csDMARD in 46.2% of patients. The prevalent route of administration at diagnosis was the intramuscular (60.5%), while at study entry (baseline) 57.6% were receiving subcutaneous MTX. Patients who required a higher MTX dose at study entry were those who received a significantly lower starting MTX dose (P<0.001). Significantly higher MTX doses were currently required in men (P<0.001), current smokers (P=0.013), and overweight patients (P=0.028), whereas patients on oral therapy received significantly lower doses of MTX (P<0.001).

CONCLUSIONS

The MARTE study confirms once again the potential of the proper use of MTX in the treatment of RA. Data from our study suggest that a higher dose of MTX should be used since the first stages in overweight patients, men, and smokers.

Modifiable environmental exposure and risk of rheumatoid arthritis-current evidence from genetic studies

Rheumatoid arthritis (RA) is a multifactorial chronic autoimmune disease, which involves a complex interplay of environmental triggers and genetic components in its etiology. It has been shown that genetics only explain about half of the liability to develop RA, leaving a large room for non-genetic factors. Indeed, several environmental exposures including smoking, drinking, obesity, and dietary patterns (and more) have been identified to be associated with RA risk, yet the observational nature of conventional epidemiological investigation hampers causal inference, as the validity of results could be plagued by measurement error, confounding, and/or reverse causality. Mendelian randomization (MR) is a novel statistical approach that uses genetic variants as instrumental variables (IV) to make causal inferences from observational data. The current genetic discoveries in the many heritable and modifiable human complex traits have provided an exceptional opportunity to evaluate a putative causal relationship between exposure and outcome in the absence of high-quality experimental or intervention studies, through a MR design. In the current review, we detail the contribution of MR studies hitherto conducted for modifiable environmental exposures with the risk of RA to understand the role of these factors in RA pathogenesis. We start with a brief introduction of each study, follow by a summarization of shortcomings and conclude by highlighting future directions. The application of MR design in the field of rheumatology remains limited. Only a few MR studies have examined the causal roles of vitamin D, cigarette smoking, alcohol consumption, coffee consumption, and levels of education in RA, where, no consistent evidence for a causal relationship has been found. Most studies lacked sensitivity analyses to verify MR model assumptions and to guarantee the validity of results. Almost all studies are likely to bias the strength of association towards a null value, since they used IVs from earlier GWAS(s) of exposures with a small sample size (i.e., few genetic markers). As the magnitudes of GWAS expand rapidly, additional trait-associated loci have been discovered. Incorporating these loci would greatly improve the strength of genetic instruments, as well as both the accuracy and precision of MR estimates. To conclude, there is a need for an update and a huge space for improvement of future MR studies in RA.

Infectious Triggers in Periodontitis and the Gut in Rheumatoid Arthritis (RA): A Complex Story About Association and Causality

Rheumatoid arthritis (RA) is a systemic immune mediated inflammatory disease of unknown origin, which is predominantly affecting the joints. Antibodies against citrullinated peptides are a rather specific immunological hallmark of this heterogeneous entity. Furthermore, certain sequences of the third hypervariable region of human leukocyte antigen (HLA)-DR class II major histocompatibility (MHC) molecules, the so called "shared epitope" sequences, appear to promote autoantibody positive types of RA. However, MHC-II molecule and other genetic associations with RA could not be linked to immune responses against specific citrullinated peptides, nor do genetic factors fully explain the origin of RA. Consequently, non-genetic factors must play an important role in the complex interaction of endogenous and exogenous disease factors. Tobacco smoking was the first environmental factor that was associated with onset and severity of RA. Notably, smoking is also an established risk factor for oral diseases. Furthermore, smoking is associated with extra-articular RA manifestations such as interstitial lung disease in anatomical proximity to the airway mucosa, but also with subcutaneous rheumatoid nodules. In the mouth, Porphyromonas gingivalis is a periodontal pathogen with unique citrullinating capacity of foreign microbial antigens as well as candidate RA autoantigens. Although the original hypothesis that this single pathogen is causative for RA remained unproven, epidemiological as well as experimental evidence linking periodontitis (PD) with RA is rapidly accumulating. Other periopathogens such as Aggregatibacter actinomycetemcomitans and Prevotella intermedia were also proposed to play a specific immunodominant role in context of RA. However, demonstration of T cell reactivity against citrullinated, MHC-II presented autoantigens from RA synovium coinciding with immunity against Prevotella copri (Pc.), a gut microbe attracted attention to another mucosal site, the intestine. Pc. was accumulated in the feces of clinically healthy subjects with citrulline directed immune responses and was correlated with RA onset. In conclusion, we retrieved more than one line of evidence for mucosal sites and different microbial taxa to be potentially involved in the development of RA. This review gives an overview of infectious agents and mucosal pathologies, and discusses the current evidence for causality between different exogenous or mucosal factors and systemic inflammation in RA.

Genetic determinants of beverage consumption: Implications for nutrition and health

Beverages make important contributions to nutritional intake and their role in health has received much attention. This review focuses on the genetic determinants of common beverage consumption and how research in this field is contributing insight to what and how much we consume and why this genetic knowledge matters from a research and public health perspective. The earliest efforts in gene-beverage behavior mapping involved genetic linkage and candidate gene analysis but these approaches have been largely replaced by genome-wide association studies (GWAS). GWAS have identified biologically plausible loci underlying alcohol and coffee drinking behavior. No GWAS has identified variants specifically associated with consumption of tea, juice, soda, wine, beer, milk or any other common beverage. Thus far, GWAS highlight an important behavior-reward component (as opposed to taste) to beverage consumption which may serve as a potential barrier to dietary interventions. Loci identified have been used in Mendelian randomization and gene×beverage interaction analysis of disease but results have been mixed. This research is necessary as it informs the clinical relevance of SNP-beverage associations and thus genotype-based personalized nutrition, which is gaining interest in the commercial and public health sectors.