CARD15 gene polymorphisms in patients with spondyloarthropathies identify a specific phenotype previously related to Crohn's disease

Sacroiliitis in inflammatory bowel disease

PURPOSE OF REVIEW

This review summarizes the recent evidence regarding the epidemiology of inflammatory bowel disease (IBD) associated sacroiliitis, including the prevalence, pathogenesis, role of imaging, and therapeutic challenges.

RECENT FINDINGS

Sacroiliitis is an underappreciated musculoskeletal manifestation of IBD, a chronic inflammatory condition of the gut affecting the younger population. Untreated sacroiliitis can lead to joint destruction and chronic pain, further adding to morbidity in IBD patients. Recent publications suggest sacroiliitis can be detected on abdominal imaging obtained in IBD patients to study bowel disease, but only a small fraction of these patients were seen by rheumatologists. Early detection of IBD-associated sacroiliitis could be achieved by utilization of clinical screening tools in IBD clinics, careful examination of existing computed tomography and MRI studies, and timely referral to rheumatologist for further evaluation and treatment. Current treatment approaches for IBD and sacroiliitis include several targeted biologic therapies, but IBD-associated sacroiliitis has limited options, as these therapies may not overlap in both conditions.

SUMMARY

With the advances in imaging, sacroiliitis is an increasingly recognized comorbidity in IBD patients. Future studies focusing on this unique patient population will expand our understanding of complex pathophysiology of IBD-associated sacroiliitis and lead to identification of novel targeted therapies for this condition.

Serum biomarkers and their relationship to axial spondyloarthritis associated with inflammatory bowel diseases

Spondyloarthritis (SpA) constitute a group of chronic inflammatory immune-mediated rheumatic diseases characterized by genetic, clinical, and radiological features. Recent efforts have concentrated on identifying biomarkers linked to axial SpA associated with inflammatory bowel disease (IBD), offering predictive insights into disease onset, activity, and progression. Genetically, the significance of the HLA-B27 antigen is notably diminished in ankylosing spondylitis (AS) associated with IBD, but is heightened in concurrent sacroiliitis. Similarly, certain polymorphisms of endoplasmic reticulum aminopeptidase (ERAP-1) appear to be involved. Carriage of variant NOD2/CARD15 polymorphisms has been demonstrated to correlate with the risk of subclinical intestinal inflammation in AS. Biomarkers indicative of pro-inflammatory activity, including C-reactive protein (CRP) along with erythrocyte sedimentation rate (ESR), are among the consistent predictive biomarkers of disease progression. Nevertheless, these markers are not without limitations and exhibit relatively low sensitivity. Other promising markers encompass IL-6, serum calprotectin (s-CLP), serum amyloid (SAA), as well as biomarkers regulating bone formation such as metalloproteinase-3 (MMP-3) and Dickkopf-related protein 1 (DKK-1). Additional candidate indicators of structural changes in SpA patients include matrix metalloproteinase-3 (MMP-3), vascular endothelial growth factor (VEGF), tenascin C (TNC), and CD74 IgG. Fecal caprotein (f-CLP) levels over long-term follow-up of AS patients have demonstrated predictive value in anticipating the development of IBD. Serologic antibodies characteristic of IBD (ASCA, ANCA) have also been compared; however, results exhibit variability. In this review, we will focus on biomarkers associated with both axial SpA and idiopathic intestinal inflammation, notably enteropathic spondyloarthritis.

Biologic Treatment Modification Efficacy in Concurrent Inflammatory Bowel Disease and Ankylosing Spondylitis: A Retrospective Cohort Study at a Single Tertiary Center

BACKGROUND

The link between ankylosing spondylitis (AS) and inflammatory bowel disease (IBD) is well-established, with concurrent prevalence estimates ranging from 5-10%. However, there are still significant gaps in our understanding, and a comprehensive treatment guideline for these co-diagnosed patients has yet to be established. Our objective was to explore patterns of treatment alterations following the diagnosis of AS in patients previously diagnosed with IBD, and vice versa. Additionally, we sought to determine how these modifications influence clinical outcomes in both conditions.

METHODS

This retrospective data-based cohort study included patients with coexisting IBD and AS that were diagnosed between the years 2009-2022 and were followed by the gastroenterology and the rheumatology units of the Sheba Medical Center, Israel. The data were extracted from the electronic health record and included demographic information, medication history, treatment modification at the time of second diagnosis, and the characteristics and activity of both IBD and AS at the index time and at the 3-month mark.

RESULTS

The study included a total of 68 patients, with a male predominance (40 patients, 59%). The median age was 43 years (IQR 31-55) and 78% had Crohn's disease (CD). The median duration between the diagnosis of the first disease to the second one was 4 years (IQR 1-9.5). A significant proportion of patients (85%) underwent treatment modification at their second diagnosis. Out of the total cohort, 28% initiated biological therapy, 17.6% switched their biologic regimen, and 16.2% discontinued NSAIDS. Patients who underwent biologic modifications at time of the second diagnosis (the initiation/switch/augmentation of a concurrent regimen) experienced significantly higher rates of clinical improvement in either IBD or AS at the 90-day follow-up compared to patients who did not (68% vs. 32%, p = 0.004), and biologic modification was found to be an independent predictor for clinical improvement (OR 3.69, CI 1.08-12.58, p = 0.037).

CONCLUSIONS

Our findings suggest that biologic therapy modification at the time of the second diagnosis was associated with a higher rate of improvement in AS/IBD at the 90-day follow-up.

SpA plus IBD or IBD plus SpA: Does commutative property apply?

The term spondyloarthritis (SpA) encompasses a group of interrelated disorders characterised by the involvement of the musculoskeletal system as well as extra-articular manifestations like acute anterior uveitis, psoriasis and inflammatory bowel diseases (IBD). Likewise, IBD may present with various extra-intestinal manifestations among which those involving the musculoskeletal system, namely peripheral and axial SpA are the most common. The identification of patients with both SpA and IBD is of paramount importance in clinical practice since the coexistence of these two entities has been associated with great disability and decreased quality of life. In order to achieve an early diagnosis of IBD-SpA it is instrumental that rheumatologists seek for gastrointestinal symptoms in SpA patients and likewise that gastroenterologists seek for inflammatory musculoskeletal symptoms in patients with IBD. This narrative review aims at critically appraising the available evidence about SpA occurring in IBD patients versus IBD occurring in patients with SpA and at highlighting similarities and differences between the two scenarios.

Inflammatory bowel disease manifestations in spondyloarthritis: considerations for the clinician

INTRODUCTION

Spondyloarthropathies (SpA) are a group of inflammatory arthritis that can involve the spine and/or peripheral joints. Extra-articular manifestations, such as inflammatory bowel disease (IBD), are frequently observed within the clinical manifestations of SpA and are part of the SpA classification criteria. Evidence of IBD is observed in about 6-7% of SpA patients, and a silent, microscopic gut inflammation, could be present in up to 50% of patients. From a pathogenetic point of view, dysregulated microbiome and migration of T lymphocytes and other cells from gut to the joint ('gut-joint' axis) has been recognized, in the context of a common genetic background.

AREAS COVERED

The aim of this paper is to narratively review the recent evidences on the epidemiology, classification, clinical findings, pathogenesis, diagnosis, and treatment of IBD in patients with SpA and to provide advices for both rheumatologist and gastroenterologist in the management of IBD in SpA.

EXPERT OPINION

IBD manifestations in SpA frequently increase the burden of the disease and represent a clinical challenge, especially for the diagnosis, assessment, and treatment of patients affected by those conditions. New treatment strategies targeting both articular and intestinal manifestations are now available and may lead to a better outcome.

Ankylosing spondylitis: an autoimmune or autoinflammatory disease?

Ankylosing spondylitis (AS) is a chronic inflammatory disorder of unknown aetiology. Unlike other systemic autoimmune diseases, in AS, the innate immune system has a dominant role characterized by aberrant activity of innate and innate-like immune cells, including γδ T cells, group 3 innate lymphoid cells, neutrophils, mucosal-associated invariant T cells and mast cells, at sites predisposed to the disease. The intestine is involved in disease manifestations, as it is at the forefront of the interaction between the mucosal-associated immune cells and the intestinal microbiota. Similarly, biomechanical factors, such as entheseal micro-trauma, might also be involved in the pathogenesis of the articular manifestation of AS, and sentinel immune cells located in the entheses could provide links between local damage, genetic predisposition and the development of chronic inflammation. Although these elements might support the autoinflammatory nature of AS, studies demonstrating the presence of autoantibodies (such as anti-CD74, anti-sclerostin and anti-noggin antibodies) and evidence of activation and clonal expansion of T cell populations support an autoimmune component to the disease. This Review presents the evidence for autoinflammation and the evidence for autoimmunity in AS and, by discussing the pathophysiological factors associated with each, aims to reconcile the two hypotheses.

[Update: enterogenic spondylarthritis]

Spondylarthritis (SpA) is one of the most frequent extraintestinal manifestations of chronic inflammatory bowel disease (IBD). Several arthritogenic enterobacterial infections can induce sequelae such as reactive SpA. Studies on the gut-synovium axis in view of genetic, immunological, clinical and therapeutic aspects has made enterogenic SpA a model disease of all forms of SpA. The same applies for investigating IBD, as subclinical gut inflammation seen in SpA patients has provided significant evidence for a better understanding of mucosa-associated early immune events in Crohn's disease (CD). This article summarizes the pathognomonic clinical features, diagnostic steps, differential diagnosis and current pathogenetic models of enterogenic SpA. Knowledge of pathogenetic contexts leads to concrete treatment recommendations. These vary individually depending on the underlying IBD, on the inflammatory intestinal or rheumatic activity and on the rheumatological manifestation pattern.

Systematic Review with Meta-analysis: The Impact of Co-occurring Immune-mediated Inflammatory Diseases on the Disease Course of Inflammatory Bowel Diseases

BACKGROUND AND AIMS

Patients with inflammatory bowel diseases (IBDs) are at risk of developing a variety of other immune-mediated inflammatory diseases (IMIDs). The influence of co-occurring IMIDs on the disease course of IBD remains unknown. The aim of this study was therefore to conduct a systematic review and meta-analysis of the impact of IMIDs on phenotypic presentation and outcome in patients with IBD.

METHODS

PubMed and Embase were searched from their earliest records through December 2018 and updated in October 2019 for studies reporting proportions or ratios of IBD-related disease outcomes in patients with and without co-occurring IMIDs. Meta-analyses were performed to estimate summary proportions and risks of the main outcomes. PRISMA guidelines were used, and study quality was assessed according to the Newcastle-Ottawa Scale.

RESULTS

A total of 93 studies were identified, comprising 16,064 IBD patients with co-occurring IMIDs and 3,451,414 IBD patients without IMIDs. Patients with IBD and co-occurring IMIDs were at increased risk of having extensive colitis or pancolitis (risk ratio, 1.38; 95% Cl, 1.25-1.52; P < 0.01, I2 = 86%) and receiving IBD-related surgeries (risk ratio, 1.17; 95% Cl, 1.01-1.36; P = 0.03; I2 = 85%) compared with patients without IMIDs. Co-occurrence of IMIDs other than primary sclerosing cholangitis in patients with IBD was associated with an increased risk of receiving immunomodulators (risk ratio, 1.15; 95% Cl, 1.06-1.24; P < 0.01; I2 = 60%) and biologic therapies (risk ratio, 1.19; 95% Cl, 1.08-1.32; P < 0.01; I2 = 53%).

CONCLUSION

This meta-analysis found that the presence of co-occurring IMIDs influences the disease course of IBD, including an increased risk of surgery and its phenotypical expression.

Putative Pathobionts in HLA-B27-Associated Spondyloarthropathy

Spondyloarthritis (SpA) is a group of immune mediated inflammatory diseases with a strong association to the major histocompatibility (MHC) class I molecule, HLA-B27. Although the association between HLA-B27 and AS has been known for almost 50 years, the mechanisms underlying disease pathogenesis are elusive. Over the years, three hypotheses have been proposed to explain HLA-B27 and disease association: 1) HLA B27 presents arthritogenic peptides and thus creates a pathological immune response; 2) HLA-B27 misfolding causes endoplasmic reticulum (ER) stress which activates the unfolded protein response (UPR); 3) HLA-B27 dimerizes on the cell surface and acts as a target for natural killer (NK) cells. None of these hypotheses explains SpA pathogenesis completely. Evidence supports the hypothesis that HLA-B27-related diseases have a microbial pathogenesis. In animal models of various SpAs, a germ-free environment abrogates disease development and colonizing these animals with gut commensal microbes can restore disease manifestations. The depth of microbial influence on SpA development has been realized due to our ability to characterize microbial communities in the gut using next-generation sequencing approaches. In this review, we will discuss various putative pathobionts in the pathogenesis of HLA-B27-associated diseases. We pursue whether a single pathobiont or a disruption of microbial community and function is associated with HLA-B27-related diseases. Furthermore, rather than a specific pathobiont, metabolic functions of various disease-associated microbes might be key. While the use of germ-free models of SpA have facilitated understanding the role of microbes in disease development, future studies with animal models that mimic diverse microbial communities instead of mono-colonization are indispensable. We discuss the causal mechanisms underlying disease pathogenesis including the role of these pathobionts on mucin degradation, mucosal adherence, and gut epithelial barrier disruption and inflammation. Finally, we review the various uses of microbes as therapeutic modalities including pre/probiotics, diet, microbial metabolites and fecal microbiota transplant. Unravelling these complex host-microbe interactions will lead to the development of new targets/therapies for alleviation of SpA and other HLA-B27 associated diseases.

Bidirectional Causal Associations Between Inflammatory Bowel Disease and Ankylosing Spondylitis: A Two-Sample Mendelian Randomization Analysis

Background

Associations between inflammatory bowel disease (IBD) [including ulcerative colitis (UC) and Crohn’s disease (CD)] and ankylosing spondylitis (AS) were discovered in observational studies, but no evidence supported the causal relationship between the two diseases.

Methods

We employed two-sample Mendelian randomization (MR) to estimate the unconfounded bidirectional causal associations between IBD (including UC and CD) and AS. We selected single-nucleotide polymorphisms (SNPs) from genome-wide association studies (GWAS) after strictly assessing the quality of the studies in the IEU GWAS database. Sensitivity analyses were also conducted to verify whether heterogeneity and pleiotropy can bias the MR results.

Results

We found positive causal effects of genetically increased UC, CD, and IBD risk on AS (e.g., UC and AS, IVW OR: 1.0256, 95% CI: 1.0130∼1.0385, p = 6.43E-05). However, we did not find significant causal associations of AS with UC, CD, or IBD (e.g., AS and UC, IVW OR: 1.1858, 95% CI: 0.8639∼1.6278, p = 0.2916). The sensitivity analysis also confirmed that horizontal pleiotropy was unlikely to bias the causality (e.g., UC and AS, MR-Egger: intercept p = 0.1326). The leave-one-out analysis also demonstrated that the observed links were not driven by SNP. No evidence of heterogeneity was found between the genetic variants (e.g., UC and AS, MR-Egger: Q statistic = 43.1297, I²<0.0001, p = 0.7434).

Conclusion

Our results provide new evidence indicating there are positive causal effects of IBD on AS in the European population. We suggest that the features of inflammatory bowel disease in particular should be assessed in the diagnosis of ankylosing spondylitis. We also provide some advice for preventing and treating the two diseases.

Revisiting the gut-joint axis: links between gut inflammation and spondyloarthritis

Gut inflammation is strongly associated with spondyloarthritis (SpA), as exemplified by the high prevalence of inflammatory bowel disease (IBD) and the even higher occurrence of subclinical gut inflammation in patients with SpA. The gut-joint axis of inflammation in SpA is further reinforced by similarities in immunopathogenesis at both anatomical sites and by the clinical success of therapies blocking TNF and IL-23 in IBD and in some forms of SpA. Many genetic risk factors are shared between SpA and IBD, and changes in the composition of gut microbiota are seen in both diseases. Current dogma is that inflammation in SpA initiates in the gut and leads to joint inflammation; however, although conceptually attractive, some research does not support this causal relationship. For example, therapies targeting IL-17A are efficacious in the joint but not the gut, and interfering with gut trafficking by targeting molecules such as α4β7 in IBD can lead to onset or flares of SpA. Several important knowledge gaps remain that must be addressed in future studies. Determining the true nature of the gut-joint axis has real-world implications for the treatment of patients with co-incident IBD and SpA and for the repurposing of therapeutics from one disease to the other.

The ties that bind: skin, gut and spondyloarthritis

PURPOSE OF REVIEW

This article aims to review recent literature linking epithelial barrier inflammation and arthritis in spondyloarthritis (SpA), with a critical view on how they are bound by genetic, immunological and environmental ties.

RECENT FINDINGS

The epithelia-joint axis has become an intense area of both basic and clinical SpA research. The penultimate goal is to understand the immunopathologic links between epithelial inflammation and arthritis in SpA. Inflammatory bowel disease (IBD) and psoriasis (PsO) have strong links to SpA at several levels. Clinically, there is a strong association of IBD, PsO and SpA. Genetically, there are many shared risk factors; however, there are also distinct differences in the genetics of the respective diseases. Immunologically, type 3 immunity, especially interleukin (IL)-17 and IL-23 dysregulation, has been shown to play a central role in IBD, PsO and SpA. Environmentally, a microbial dysbiosis has been noted in each of these diseases, but whether the microbial signature is similar between diseases is not clear, nor is the effect of dysbiosis on the immune response known.

SUMMARY

It will be crucial to determine whether the relationship between epithelia inflammation and SpA is truly causal for both the understanding of pathogenesis and for future treatment strategies.

Biomarkers in Inflammatory Bowel Disease-Associated Spondyloarthritis: State of the Art and Unmet Needs

Inflammatory bowel disease-associated spondyloarthritis is a systemic disease characterized by the chronic inflammation of both the gastrointestinal tract and the musculoskeletal system. Since inflammatory bowel disease-associated spondyloarthritis has been associated with a significant diagnostic delay, which may lead to poor quality of life and progression of joint damage, efforts to discover new reliable and noninvasive diagnostic biomarkers have been made. We reviewed the state of the art of biomarker research in inflammatory bowel disease-associated spondyloarthritis, showing that to date it has been largely unsatisfactory. Only a few of the biomarkers that have been investigated are likely to enter the clinical practice upon further validation in independent cohorts. The research of new and innovative biomarkers for inflammatory bowel disease-associated spondyloarthritis is warranted.

Inflammatory bowel diseases and spondyloarthropathies: From pathogenesis to treatment

Spondyloarthropathies (SpA) include many different forms of inflammatory arthritis and can affect the spine (axial SpA) and/or peripheral joints (peripheral SpA) with Ankylosing spondylitis (AS) being the prototype of the former. Extra-articular manifestations, like uveitis, psoriasis and inflammatory bowel disease (IBD) are frequently observed in the setting of SpA and are, in fact, part of the SpA classification criteria. Bowel involvement seems to be the most common of these manifestations. Clinically evident IBD is observed in 6%-14% of AS patients, which is significantly more frequent compared to the general population. Besides, it seems that silent microscopic gut inflammation, is evident in around 60% in AS patients. Interestingly, occurrence of IBD has been associated with AS disease activity. For peripheral SpA, two different forms have been proposed with diverse characteristics. Of note, SpA (axial or peripheral) is more commonly observed in Crohn's disease than in ulcerative colitis. The common pathogenetic mechanisms that explain the link between IBD and SpA are still ill-defined. The role of dysregulated microbiome along with migration of T lymphocytes and other cells from gut to the joint ("gut-joint" axis) has been recognized, in the context of a genetic background including associations with alleles inside or outside the human leukocyte antigen system. Various therapeutic modalities are available with monoclonal antibodies against tumour necrosis factor, interleukin-23 and interleukin-17, being the most effective. Both gastroenterologists and rheumatologists should be alert to identify the co-existence of these conditions and ideally follow-up these patients in combined clinics.

Detection of Crohn Disease in Patients with Spondyloarthropathy: The SpACE Capsule Study

OBJECTIVE

Inflammatory bowel disease (IBD) is generally reported to be associated with spondylarthropathies (SpA) in 5%-15% of cases. Systematic colonoscopic assessment by protocol demonstrated mucosal inflammation characteristic of Crohn disease (CD) in up to one-third of patients with SpA. Video capsule endoscopy (CE) is a superior diagnostic tool to detect small bowel mucosal disease. Our study compared the accuracy of CE to standard colonoscopy for detection of inflammatory bowel lesions in patients with SpA, and to describe predictors of small bowel inflammation (SBI) in this cohort.

METHODS

Prospective cross-sectional study of adult patients followed for SpA. Patients were evaluated by CE and standard colonoscopy with biopsies. SBI was quantified using the Lewis Score. Additional screening tests included fecal calprotectin (FCP), C-reactive protein (CRP), and a diagnostic panel of serologic, inflammatory and genetic tests (SGI).

RESULTS

There were 64 patients recruited (53% female, mean age 42 ± 13 yrs). Chronic gastrointestinal (GI) symptoms were present in 57%. CE revealed significant SBI in 27/64 (42.2%), compared to 7/64 (10.9%) by standard colonoscopy (p = 0.035). Elevated FCP was associated with small bowel CD (OR 4.5, 95% CI 1.01-19.9; p = 0.042). No correlation was observed with presence of GI symptoms, CRP, or SGI results. Finding CD led to a change in management in 65.2% of cases.

CONCLUSION

CE uncovered SBI consistent with CD in 42.2% of patients with SpA, with a significant incremental yield over colonoscopy of 31%. FCP levels were significantly correlated with CE results, while GI symptoms and SGI results were poor predictors of SBI.

Gastrointestinal and Hepatic Disease in Spondyloarthritis

The association of inflammatory arthritis with intestinal pathology extends back more than 100 years. This association is now supported by epidemiologic studies demonstrating an elevated prevalence of inflammatory bowel disease in spondyloarthritis and vice versa, compared with the general population. Genetic and intestinal microbiome studies have further linked these diseases. Although diabetes and nonalcoholic fatty liver disease disproportionately affect individuals with psoriatic arthritis, diseases of the esophagus, stomach, pancreas, and liver are not particularly common in spondyloarthritis. Clinicians should be aware of the differential diagnosis and the appropriate diagnostic tools available when evaluating digestive and hepatic disorders in spondyloarthritis.

Chronic bowel inflammation and inflammatory joint disease: Pathophysiology

Bowel inflammation is closely linked to chronic joint inflammation. Research reported in the 1980s demonstrated bowel inflammation with gross and microscopic pathological features identical to those of Crohn's disease in over 60% of patients with spondyloarthritis (SpA). Numerous prospective studies have evidenced joint involvement in patients with chronic inflammatory bowel disease (IBD) and bowel inflammation in patients with SpA. Nevertheless, the interactions of joint disease and chronic bowel inflammation remain incompletely elucidated. Two main hypotheses have been suggested to explain potential links between inflammation of the mucosal immune system and peripheral arthritis: one identifies gut bacteria as potentially implicated in the development of joint inflammation and the other involves the recruitment of gut lymphocytes or activated macrophages to the joints. Pathophysiological investigations have established that HLA-B27 is a pivotal pathogenic factor. Here, we review current data on links between chronic bowel inflammation and inflammatory joint disease.

Autophagy-related IRGM genes confer susceptibility to ankylosing spondylitis in a Chinese female population: a case-control study

It is known that ankylosing spondylitis (AS) and inflammatory bowel disease (IBD) shared a common genetic component. The gist of current study is to assess the role of IBD-associated autophagy gene IRGM on AS susceptibility in a Chinese Han population. A total of 1270 unrelated subjects (643 AS and 627 controls) were enrolled. Two tag single-nucleotide polymorphisms (SNPs) (rs10065172 and rs4958846) were selected and were genotyped by iMLDR Assay technology. Genotypes and haplotype analysis were conducted by using SPSS 16.0 and haploview 4.2 software. Among two tag SNPs of IRGM, no correlation was observed between rs10065172 and AS susceptibility. For rs4958846, genotype and allelic frequencies were marginally discrepant between female cases and controls before, not after, Bonferroni correction (P=0.049; P=0.031). Logistic regression analysis revealed that carriers with CT+TT or CT genotype had a significantly decreased risk for developing AS among female subjects when compared with CC genotype (OR=0.514, 95% CI=0.301-0.876, P=0.014; OR=0.518, 95% CI=0.297-0.902, P=0.020, respectively). Additionally, a risk haplotype rs4958846^C-rs10065172^C (OR=2.093, 95% CI=1.301-3.368) and a protective haplotype rs4958846^T-rs10065172^C (OR=0.652, 95% CI=0.441-0.964) were also identified to be associated with female AS. IBD-associated IRGM gene is also associated with AS susceptibility in the Chinese female population, indicating that autophagy pathway may involve in AS genetic predisposition.

NOD2/CARD15 gene mutations in patients with gouty arthritis

Nucleotide binding and oligomerization domains/caspase recruitment domain-containing protein 15 (NOD2/CARD15) is a cytoplasmic molecule controlling apoptosis and inflammatory processes by recognizing some microbial components. We aimed to identify the frequencies of NOD2/CARD15 gene mutations in patients with gouty arthritis and to determine their possible correlation with the disease phenotype. The study included 93 patients with gouty arthritis and 51 healthy controls matched for age, gender, and ethnicity. The NOD2/CARD15 R702W and G908R gene mutations were explored by the polymerase chain reaction restriction fragment length polymorphism method while the 3020insC mutation was analyzed by DNA sequencing. The mean patient age was 54.2 ± 14.2 years and mean duration of the disease was 3.1 ± 2.9 years. The first metatarsophalangeal and finger joint involvements were detected in 72 (77.4%) and 18 (19.5%) patients, respectively. Ankle arthritis and knee arthritis were detected in 43 (46.2%) and 20 (21.5%) patients, respectively. In total, 4 (9%) heterozygous mutations were detected in the G908R and R702W genes, while no mutation was detected in the 3020insC gene. Compared to the control group, there were no significant differences in all three DNA regions (G908R, R702W, and 3020insC; p = 0.452, p = 0.583, and p = 0.350, respectively). No correlation between the NOD2/CARD15 variants and clinical or laboratory findings (p > 0.05) was found. The frequencies of the NOD2/CARD15 gene mutations in the patients were similar to healthy control group. No association between clinical or laboratory findings and the NOD2/CARD15 gene mutations was observed.

The intestinal microbiome in spondyloarthritis

PURPOSE OF REVIEW

Microbial dysbiosis in the gut is emerging as a common component in various inflammatory disorders including spondyloarthritis (SpA). The depth of this influence has begun to be realized with next-generation sequencing of the gut microbiome providing unbiased assessment of previously uncharted bacterial populations.

RECENT FINDINGS

Decreased numbers of Firmicutes, a major phyla of gut commensals, especially the species Faecalibacterium prausnitzii and Clostridium leptum have been found in various inflammatory disorders including SpA and inflammatory bowel disease (IBD), and could be an important link between SpA and gut inflammation. Multiple studies in ankylosing spondylitis, psoriatic arthritis, juvenile SpA, and animal models of SpA are revealing common bacterial associations among these diseases as well as IBD.

SUMMARY

We are beginning to appreciate the complex relationship between the gut microbiome and host immune regulation and dysregulation in health and disease. Potentially important differences have been revealed in SpA, but cause and effect relationships remain far from established. Many critical questions remain to be answered before we can apply new knowledge to improve therapeutics in SpA.

Importance of intestinal microenvironment in development of arthritis. A systematic review

A strong connection between spondylarthropathies and inflammatory bowel diseases (IBD) is well established. About 10-15% of IBD are associated with different forms of spondylarthritis. Arthritis can be manifested as axial, peripheral form or both. The primary functions of the gastrointestinal tract are digestion and absorption of nutrients, electrocytes and maintenance of water homoeostasis. The anatomic and functional lesions could lead to the development of IBD based on molecular mimicry and bystander effects. The mechanism of the macromolecules is uptaken may affect intestinal and extraintestinal manifestation in genetically susceptible individuals by gut-associated lymphoid tissue, the interplay between innate and adaptive immunity and the neuroendocrine network.

Spondyloarthritis and the microbiome: new insights from an ancient hypothesis

The human microbiome, which represents the total collection of microorganisms (and their genes) inhabiting the human body, has increasingly been recognized as a potential key factor in the development of autoimmune disease. Multiple studies suggest that the microbiome has significant influence on immune homeostasis, while disruptions in local microbiome composition can result in a heightened systemic inflammatory response. The intestinal microbiome, in particular, harbors the densest assembly of bacteria and appears to influence the immune system in the context of inflammatory arthropathies. Although studies are still sparse, this review will examine the role of the microbiome in the pathogenesis of spondyloarthritis (SpA), particularly in enteropathic arthritis (EA), reactive arthritis (ReA), ankylosing spondylitis (AS), and psoriatic arthritis (PsA).

Occult spondyloarthritis in inflammatory bowel disease

Spondyloarthritis (SpA) is a frequent extra-intestinal manifestation in patients with inflammatory bowel disease (IBD), although its real diffusion is commonly considered underestimated. Abnormalities in the microbioma and genetic predisposition have been implicated in the link between bowel and joint inflammation. Otherwise, up to date, pathogenetic mechanisms are still largely unknown and the exact influence of the bowel activity on rheumatic manifestations is not clearly explained. Due to evidence-based results of clinical studies, the interest on clinically asymptomatic SpA in IBD patients increased in the last few years. Actually, occult enthesitis and sacroiliitis are discovered in high percentages of IBD patients by different imaging techniques, mainly enthesis ultrasound (US) and sacroiliac joint X-ray examinations. Several diagnostic approaches and biomarkers have been proposed in an attempt to correctly classify and diagnose clinically occult joint manifestations and to define clusters of risk for patient screening, although definitive results are still lacking. The correct recognition of occult SpA in IBD requires an integrated multidisciplinary approach in order to identify common diagnostic and therapeutic strategies. The use of inexpensive and rapid imaging techniques, such as US and X-ray, should be routinely included in daily clinical practice and trials to correctly evaluate occult SpA, thus preventing future disability and worsening of quality of life in IBD patients.

Gut microbes, immunity, and spondyloarthritis

The last decade has witnessed an explosion of studies evaluating the impact of the human microbiota on a variety of disease states. The microbiota can impact diseases in multiple ways, including through abnormalities in the diversity and contents of the microbiota, as well as by acting as targets of immunologic dysregulation. Herein, evidence that the microbiota in spondyloarthritis is both altered and abnormally targeted by the immune system will be presented.

The role of the gut and microbes in the pathogenesis of spondyloarthritis

The intestinal microbiota is firmly implicated not only in the pathogenesis of inflammatory bowel disease (IBD) but increasingly also in the development of inflammation at extraintestinal tissue sites. Significant clinical, genetic, immunological, and microbiological overlap exists between IBD and spondyloarthritis (SpA), which indicates that pathophysiological mechanisms are shared between these diseases and may center on the intestinal microbiota. Recently, culture-independent techniques have enabled the microbiota in health and disease to be described in increasing detail. Moreover, functional studies have identified myriad host effector and regulatory pathways that shape or are shaped by this microbial community. We consider the complex relationship between SpA pathogenesis and gut microbes, with a discussion of how manipulation of the gut microbiota itself may be a promising future target for SpA therapy.

Spondyloarthritis and inflammatory bowel disease. Comorbidity and treatment implications

Spondyloarthritides (SpA) and inflammatory bowel disease (IBD) are chronic, idiopathic inflammatory disorders of the axial and peripheral joints and the intestinal tract, respectively, affecting up to 1 % of the population. There is clinical and genetic evidence supporting some degree of overlap between the pathogenesis of these two entities. Nevertheless, their treatment is at times conflicting. NSAIDs, although useful in SpA, are considered to be possible risk factors for flares in IBD. Moreover, etanercept, a soluble TNF receptor blocker used in SpA, is ineffective in IBD. As patients with SpA often develop microscopic gut inflammation, it is important to understand the impact on disease progression or even therapeutic response. Further research is mandatory in this regard.

Osteoarticular manifestations: specific treatments and/or treating intestinal disease?

Osteoarticular manifestations in inflammatory bowel diseases (IBD) belong to the concept of spondyloarthritis (SpA) including an axial and peripheral SpA according to predominant symptoms (inflammatory back pain vs. peripheral arthritis and enthesopathy). Careful examination of sacroiliac joints on MRI plays a crucial role in the recognition of an early axial SpA in young patients with inflammatory back pain and spinal inflammation on MRI but without structural changes on radiography (non-rx SpA). In this early form of SpA, chronic gut inflammation was already found in about 30% of patients. Moreover, more pronounced bone marrow edema was found in patients with axial SpA and chronic gut inflammation. Identification of a therapeutic window in patients with early gut and spine inflammation is important since anti-TNF suppresses inflammation and seems to prevent evolution to structural changes. Shared genetic factors probably predispose to both diseases. Careful analysis of the effect of medication on gut and spine inflammation in SpA and IBD patients is recommended in order to find new therapeutic agents.

Enteropathic spondyloarthritis: from diagnosis to treatment

Enteropathic arthritis (EA) is a spondyloarthritis (SpA) which occurs in patients with inflammatory bowel diseases (IBDs) and other gastrointestinal diseases. Diagnosis is generally established on the medical history and physical examination. It was, generally, made according to the European Spondyloarthropathy Study Group (ESSG) criteria. Rheumatic manifestations are the most frequent extraintestinal findings of IBD with a prevalence between 17% and 39%, and IBD is associated, less frequently, with other rheumatic disease such as rheumatoid arthritis, Sjogren syndrome, Takayasu arteritis, and fibromyalgia. Although the pathogenesis of EA has not been plainly clarified, the most popular theory supposes that joint inflammation occurs in genetically predisposed subjects with bacterial gut infections, provided an important evidence for a possible relationship between inflammation of the gut mucosa and arthritis. The management of patients with EA requires an active cooperation between the gastroenterologist and rheumatologist.

The transition of acute to chronic bowel inflammation in spondyloarthritis

That gut and joint inflammation are linked in spondyloarthritis (SpA) has been recognized for almost three decades. Intriguingly, microscopic gut inflammation, which occurs frequently in patients with SpA, is an important risk factor for clinically overt Crohn's disease and ankylosing spondylitis. This Review describes current insights into the underlying mechanisms that lead to chronic gut inflammation in patients with SpA. We propose that the development of chronic bowel inflammation in these individuals occurs through a transition phase, in which inflammation evolves from an acute into a chronic state. Our transition model implies that different cell types are involved at different stages during disease progression, with stromal cells having an important role in chronicity. In addition, deficient regulatory feedback mechanisms or genetically determined alterations in antigen presentation, endoplasmic reticulum stress, autophagy or cytokine signaling might also favor a transition from self-limiting acute inflammation to chronic inflammation. We anticipate that this transition phase might be an important window for therapeutic intervention.

Ubiquitination and phosphorylation in the regulation of NOD2 signaling and NOD2-mediated disease

The immune system is exquisitely balanced. It has the ability to effectively respond to and control infections while at the same time preventing inappropriate responses to self and environmental antigens. When this response goes awry, either through a failure to activate the immune response, or failure to terminate it, inflammatory pathology results. Posttranslational modifications (PTMs) such as ubiquitination and phosphorylation help ensure that the delicate balance underlying immune signal transduction is maintained. Ubiquitination and phosphorylation affect localization, activity, stability, and interactions of various components of the immune signal transduction machinery. Moreover, ubiquitination and phosphorylation are tightly linked, with one PTM affecting the other. Therefore, in order to find potential therapies for many immune-related pathologies, it is necessary to understand not only how the immune response is activated by ubiquitination and phosphorylation, but also how it is regulated by these PTMs at different stages of the response. An excellent system to study such activation and regulation is the NOD2 pathway. Dysregulation of NOD2 signaling is involved in the pathogenesis of a variety of inflammatory disorders including Crohn's disease, early onset sarcoidosis, and Blau syndrome. More recently NOD2 has been implicated in the development of autoimmune disease, allergy and asthma. This review will focus on what is currently known about how ubiquitination and phosphorylation regulate NOD2 signaling with particular emphasis on novel in vitro substrates which may serve as potential in vivo therapeutic targets for hyperactive NOD2 states. This article is part of a Special Issue entitled: Ubiquitin Drug Discovery and Diagnostics.

Role of genetics in the diagnosis and prognosis of Crohn's disease

Considering epidemiological, genetic and immunological data, we can conclude that the inflammatory bowel diseases are heterogeneous disorders of multifactorial etiology in which hereditability and environment interact to produce the disease. It is probable that patients have a genetic predisposition for the development of the disease coupled with disturbances in immunoregulation. Several genes have been so far related to the diagnosis of Crohn's disease. Those genes are related to innate pattern recognition receptors, to epithelial barrier homeostasis and maintenance of epithelial barrier integrity, to autophagy and to lymphocyte differentiation. So far, the most strong and replicated associations with Crohn's disease have been done with NOD2, IL23R and ATG16L1 genes. Many genes have so far been implicated in prognosis of Crohn's disease and many attempts have been made to classify genetic profiles in Crohn's disease. CARD15 seems not only a susceptibility gene, but also a disease-modifier gene for Crohn's disease. Enriching our understanding on Crohn's disease genetics is important but when combining genetic data with functional data the outcome could be of major importance to clinicians.

Role of genetics in the diagnosis and prognosis of Crohn's disease

Considering the epidemiological, genetic and immunological data, we can conclude that the inflammatory bowel diseases are heterogeneous disorders of multifactorial etiology in which hereditability and environment interact to produce the disease. It is probable that patients have a genetic predisposition for the development of the disease coupled with disturbances in immunoregulation. Several genes have so far been related to the diagnosis of Crohn's disease. These genes are related to innate pattern recognition receptors, to epithelial barrier homeostasis and maintenance of epithelial barrier integrity, to autophagy and to lymphocyte differentiation. So far, the strongest and most replicated associations with Crohn's disease have been demonstrated with NOD2, IL23R and ATG16L1 genes. Many genes have so far been implicated in the prognosis of Crohn's disease and many attempts have been made for classification of genetic profiles in Crohn's disease. CARD15 seems to be not only a susceptibility gene, but also a disease-modifier gene for Crohn's disease. Enriching our understanding of Crohn's disease genetics is of value, but when combining genetic data with functional data the outcome could be of major importance to clinicians.

Inflammatory bowel disease associated arthropathy

Arthritis is the most common extraintestinal manifestation of inflammatory bowel disease (IBD) and can have a significant impact on morbidity and quality of life. IBD-associated arthropathy is considered a subtype of seronegative spondyloarthropathy, with axial, peripheral, or a combination of both joint manifestations. Peripheral arthritis is generally non-erosive and the oligoarticular variant particularly may correlate with intestinal disease activity. Axial arthritis may include inflammatory back pain, sacroiliitis, or ankylosing spondylitis, and is less likely to correlate with gastrointestinal symptoms. While there have been advances in identifying predisposing genetic factors and in elucidating pathophysiology of inflammatory bowel disease, the mechanisms surrounding the development of arthritis in IBD remain unclear. Treatment of inflammatory bowel disease is not always sufficient for control of arthritis. While treatment with biologic agents is promising, there remains a great need for larger, randomized studies to address optimal therapy of IBD associated arthropathy.

Novel development in extraintestinal manifestations and spondylarthropathy

The important co-existence of spondylarthritis (SpA) and inflammatory bowel disease (IBD) within the same individual suggests common etiopathogenic mechanisms. This is supported by intriguing similarities between both diseases at the subclinical and molecular level. The recent advances in IBD genetics have led to the identification of common pathways involved in both IBD and SpA, including bacterial recognition and ER stress. This offers the opportunity to develop potential new therapeutic strategies for both diseases. Transgenic animals which develop both joint and gut inflammation (like the TNF(ΔARE) mice and the HLA-B27 transgenic rats) are a very useful tool to test such novel therapeutics and to get further mechanistic insight into the pathogenetic link between SpA and IBD. This review will focus on the recent scientific progress in our understanding of the link between SpA and IBD. Based on this, potential novel therapeutic strategies are discussed.

Evidence for significant overlap between common risk variants for Crohn's disease and ankylosing spondylitis

Background

A multicenter genome-wide association scan for Crohn's Disease (CD) has recently reported 40 CD susceptibility loci, including 29 novel ones (19 significant and 10 putative). To gain insight into the genetic overlap between CD and ankylosing spondylitis (AS), these markers were tested for association in AS patients.

Principal Findings

Two previously established associations, namely with the MHC and IL23R loci, were confirmed. In addition, rs2872507, which maps to a locus associated with asthma and influences the expression of the ORMDL3 gene in lymphoblastoid cells, showed a significant association with AS (p = 0.03). In gut biopsies of AS and CD patients, ORMDL3 expression was not significantly different from controls and no correlation was found with the rs2872507 genotype (Spearman's rho: −0.067). The distribution of p-values for the remaining 36 SNPs was significantly skewed towards low p-values unless the top 5 ranked SNPs (ORMDL3, NKX2–3, PTPN2, ICOSLG and MST1) were excluded from the analysis.

Conclusions

Association analysis using risk variants for CD led to the identification of a new risk variant associated with AS (ORMDL3), underscoring a role for ER stress in AS. In addition, two known and five potentially relevant associations were detected, contributing to common susceptibility of CD and AS.

Interactions between gut inflammation and arthritis/spondylitis

PURPOSE OF REVIEW

The spectrum of spondyloarthritis is characterized by the intriguing co-occurrence of gut and joint inflammation, although no obvious anatomical link exists.

RECENT FINDINGS

Data from animal models identify stromal cells as important players in pathogenesis, although signalling through TNFRI appeared to be sufficient for development of combined gut and joint inflammation. Interleukin-23 receptor was identified as a susceptibility locus for ankylosing spondylitis.

SUMMARY

Human genome studies combined with animal model research provide us with new evidence in the fascinating field of the gut-joint axis. However, how these newly identified genetic associations can influence the immunological environment remains to be elucidated.

The joint-gut axis in inflammatory bowel diseases

Inflammatory bowel diseases, Crohn's disease and ulcerative colitis, are associated with a variety of extraintestinal manifestations. The most common extraintestinal manifestation, articular involvement, occurs in 16% to 33% of inflammatory bowel disease patients. These arthropathies may increase morbidity, resulting in a worse quality of life compared with inflammatory bowel disease patients without arthropathies. Thus, arthropathies in inflammatory bowel diseases represent a major medical problem in these patients. Arthritis associated with inflammatory bowel diseases is one of the diseases captured under the umbrella of spondyloarthritis. Spondyloarthritis is a group of inflammatory diseases with overlapping features and is linked to Human Leukocyte Antigen-B27. Arthropathy in inflammatory bowel diseases is clinically divided into peripheral and axial involvement. Peripheral arthritis often flares with relapses of bowel disease resulting in a different treatment approach than axial arthritis in which the course is independent of inflammatory bowel disease activity. Definitions, prevalence, pathophysiology and treatment of the arthropathies commonly seen in inflammatory bowel diseases such as peripheral arthritis, dactylitis, enthesitis, arthralgia, sacroiliitis, inflammatory back pain and ankylosing spondylitis are summarized.

Extraintestinal manifestations of inflammatory bowel disease: epidemiology, diagnosis, and management

Abstract Extraintestinal manifestations occur rather frequently in inflammatory bowel disease (IBD), e.g. ulcerative colitis (UC) and Crohn's disease (CD). The present paper provides an overview of the epidemiology, clinical characteristics, diagnostic process, and management of rheumatic, metabolic, dermatologic (mucocutaneous), ophthalmologic, hepatobiliary, hematologic, thromboembolic, urinary tract, pulmonary, and pancreatic extraintestinal manifestations related to IBD. Articles were identified through search of the PubMed and Embase databases, the Cochrane Library, and the web sites of the European Agency for the Evaluation of Medicinal Products (EMEA) and the US Food and Drug Administration (FDA) (cut-off date October 2009). The search terms 'Crohn's disease', 'inflammatory bowel disease', or 'ulcerative colitis' were combined with the terms 'adalimumab', 'anemia', 'arthritis', 'bronchiectasis', 'bronchitis', 'cutaneous manifestations', 'erythema nodosum', 'extraintestinal manifestations', 'hyperhomocysteinemia', 'infliximab', 'iridocyclitis', 'lung disease', 'ocular manifestations', 'osteomalacia', 'pancreatitis', 'primary sclerosing cholangitis', 'renal stones', 'sulfasalazine', 'thromboembolism', and 'treatment'. The search was performed on English-language reviews, practical guidelines, letters, and editorials. Articles were selected based on their relevance, and additional papers were retrieved from their reference lists. Since some of the diseases discussed are uncommon, valid evidence of treatment was difficult to obtain, and epidemiologic data on the rarer forms of extraintestinal manifestations are scarce. However, updates on the pathophysiology and treatment regimens are given for each of these disorders. This paper offers a current review of original research papers and randomized clinical trials, if any, within the field and makes an attempt to point out practical guidelines for the diagnosis and treatment of various extraintestinal manifestations related to IBD.

Joint involvement in inflammatory bowel disease: managing inflammation outside the digestive system

Joint inflammation is present in approximately 30% of patients with inflammatory bowel disease. Peripheral arthritis can frequently be controlled by an optimal treatment of the gut inflammation in association with short-term use of NSAIDs. Recurrent inflammation requires the use of sulfasalazine. More therapy-resistant forms and axial arthropathy can be treated with anti-TNF drugs, predominantly infliximab and adalimumab. An intensified multidisciplinary approach in research and in the clinic may help to unravel the question of why common etiopathogenic mechanisms ultimately lead to different disease phenotypes. Animal models may help to identify the most promising therapeutic strategies including in the near future modulation of adhesion molecules, costimulatory molecules and the Th17 pathway.

Rheumatic manifestations of inflammatory bowel disease

This article reviews the literature concerning rheumatic manifestations of inflammatory bowel disease (IBD), including common immune-mediated pathways, frequency, clinical course and therapy. Musculoskeletal complications are frequent and well-recognized manifestations in IBD, and affect up to 33% of patients with IBD. The strong link between the bowel and the osteo-articular system is suggested by many clinical and experimental observations, notably in HLA-B27 transgenic rats. The autoimmune pathogenic mechanisms shared by IBD and spondyloarthropathies include genetic susceptibility to abnormal antigen presentation, aberrant recognition of self, the presence of autoantibodies against specific antigens shared by the colon and other extra-colonic tissues, and increased intestinal permeability. The response against microorganisms may have an important role through molecular mimicry and other mechanisms. Rheumatic manifestations of IBD have been divided into peripheral arthritis, and axial involvement, including sacroiliitis, with or without spondylitis, similar to idiopathic ankylosing spondylitis. Other periarticular features can occur, including enthesopathy, tendonitis, clubbing, periostitis, and granulomatous lesions of joints and bones. Osteoporosis and osteomalacia secondary to IBD and iatrogenic complications can also occur. The management of the rheumatic manifestations of IBD consists of physical therapy in combination with local injection of corticosteroids and nonsteroidal anti-inflammatory drugs; caution is in order however, because of their possible harmful effects on intestinal integrity, permeability, and even on gut inflammation. Sulfasalazine, methotrexate, azathioprine, cyclosporine and leflunomide should be used for selected indications. In some cases, tumor necrosis factor-α blocking agents should be considered as first-line therapy.

Non-invasive investigation in patients with inflammatory joint disease

Gut inflammation can occur in 30%-60% of patients with spondyloarthropathies. However, the presence of such gut inflammation is underestimated, only 27% of patients with histological evidence of gut inflammation have intestinal symptoms, but subclinical gut inflammation is documented in two-thirds of patients with inflammatory joint disease. There are common genetic and immunological mechanisms behind concomitant inflammation in the joints and intestinal tract. A number of blood tests, e.g. erythrocyte sedimentation rate, orosomucoid, C-reactive protein, and white cell and platelet counts, are probably the most commonly used laboratory markers of inflammatory disease, however, these tests are difficult to interpret in arthropathies associated with gut inflammation, since any increases in their blood levels might be attributable to either the joint disease or to gut inflammation. Consequently, it would be useful to have a marker capable of separately identifying gut inflammation. Fecal proteins, which are indirect markers of neutrophil migration in the gut wall, and intestinal permeability, seem to be ideal for monitoring intestinal inflammation: they are easy to measure non-invasively and are specific for intestinal disease in the absence of gastrointestinal infections. Alongside the traditional markers for characterizing intestinal inflammation, there are also antibodies, in all probability generated by the immune response to microbial antigens and auto-antigens, which have proved useful in establishing the diagnosis and assessing the severity of the condition, as well as the prognosis and the risk of complications. In short, non-invasive investigations on the gut in patients with rheumatic disease may be useful in clinical practice for a preliminary assessment of patients with suspected intestinal disease.

Enteropathic spondyloarthropathy: a common genetic background with inflammatory bowel disease?

The association between spondyloarthropathy and inflammatory bowel disease (IBD) is largely established, although prevalence is variable because of different population selection and diagnostic methodologies. Most studies indicate that as many as 10%-15% of cases of IBD are complicated by ankylosing spondylitis (AS) or other forms of spondylarthritis (SpA). Of note, ileal inflammation resembling IBD has been reported in up to two thirds of cases of SpA, and it has been suggested that the presence of ileitis is associated with the chronicity of articular complications. Although this observation is of interest to unravel the pathophysiology of the disease, systematic screening of patients with SpA by ileocolonoscopy is not indicated in the absence of gut symptoms, as only a small proportion of patients with subclinical gut inflammation will develop overt IBD over time. The existence of familial clustering of both IBD and AS, the coexistence of both conditions in a patient, the evidence of an increased risk ratio among first- and second-degree relatives of affected AS or IBD patients and finally, the increased cross-risk ratios between AS and IBD, strongly suggest a shared genetic background. So far, however, IL23R is the only identified susceptibility gene shared by both IBD and AS. Although functional studies are still needed to better understand its pathogenic role, great effort is being spent therapeutically targeting this pathway that may prove effective for both disorders.