Genetics of rheumatoid arthritis: time for a change!

Exploring the pathogenesis of RA through the gut-articular axis-dysbiosis a potential factor

Rheumatoid arthritis (RA) is a chronic autoimmune disease with a complex etiology. It has been suggested that the pathogenesis of RA begins in the mucosa and then transitions to the joints when many factors interact, including microbial dysbiosis, inflammatory responses, and immune abnormalities at the mucosal site. Data from RA animals and patients suggest there are changes in the mucosal microflora before the onset of RA, and that dysbiosis of the mucosal ecology continues to play a role in the development of arthritis. Microbial dysbiosis of the mucosa reduces the normal barrier function of the intestinal tract, promotes inflammatory reactions in the mucosal areas of the intestines, and then activates the intestinal immune cells abnormally to produce a large number of auto-reactive antibodies that exacerbate arthritis. Current findings do not clarify whether dysbiosis is only a potential trigger for the development of RA. If it is possible to intervene in such microbial changes before the onset of RA, could the clinical symptoms of arthritis be prevented or reduced? Finding new ways to regulate gut flora composition to maintain gut barrier function is an ongoing challenge for the prevention and treatment of RA.

Association of Hematological and Biochemical Parameters and HLA-DRB1 Alleles With Anti-cyclic Citrullinated Peptide Autoantibodies in Sudanese Rheumatic Patients

Introduction Anti-citrullinated protein/peptide antibodies (ACPA) are crucial for the diagnosis and prognosis of rheumatoid arthritis (RA) and are associated with class II HLA-DRB1 alleles. The study's goal was to determine how DRB1 alleles and hematological and biochemical parameters affect ACPA production in RA patients from Sudan. Methods The study analyzed the hematological and biochemical parameters and the frequency of HLA-DRB1 alleles in 120 RA patients and 100 controls. Automated analyzers, ELISA, the latex agglutination test, and the Westergren method were utilized for hematological and biochemical testing. HLA class II alleles were genotyped using polymerase chain reaction-sequence-specific primers (PCR-SSP). The student's t-test and the chi-square (Χ2) test were employed to identify significant alterations between the examined parameters and allele frequencies. Results A total of 51.7% of 120 RA patients tested positive for ACPA (ACPA+). Among those patients, the DRB1*04 and *10 alleles were significantly more prevalent (22.2% vs. 8.9%, P = 0.048 and 23.8% vs. 8.9%, P = 0.030, respectively). RA patients had significantly higher counts of platelet count test (PLT; P = 0.011), lymphocytes (LY; P = 0.000), neutrophils (NE; P = 0.025), monocytes (MO; P = 0.000), eosinophils (EO; P = 0.000), neutrophil-to-lymphocyte ratio (NLR; P = 0.006), C-reactive protein (CRP; P = 0.000), and erythrocyte sedimentation rate (ESR; P = 0.000) than controls. Patients also showed low counts of red blood cells (RBC; P = 0.003), hemoglobin (Hb; P = 0.024), mean platelet volume (MPV; P = 0.000), and basophils (BA; P = 0.048). ACPA+ RA patients had elevated white blood cells (WBC; P = 0.046), PLT (P = 0.029), and low mean corpuscular hemoglobin concentration (MCHC; P = 0.022). The hematological and biochemical parameters of ACPA+ RA patients with the DRB1*04 or *10 alleles did not differ significantly. Conclusions We found significant differences in hematological and biochemical parameters between RA patients and controls that had nothing to do with ACPA positivity or the frequency of DRB1*04 or *10 alleles.

The Association of Human Leukocyte Antigen Genotyping Among Sudanese Patients With Rheumatoid Arthritis: Reference to Ethnicity

INTRODUCTION

 Human leukocyte antigens (HLA) account for up to one-half of the total genetic contribution to rheumatoid arthritis (RA) risk. The study investigated the association of HLA class II genotyping with RA susceptibility in Sudanese ethnic groups.

METHODS

 The DRB1 and DQB1 alleles and haplotypes were determined in 122 RA patients (i.e., Gaalia = 54, Johayna = 24, Baggara = 17, Nile Nubian = 12, and others = 15) and 120 healthy controls of ethnic groups (i.e., Gaalia = 44, Johayna = 11, Baggara = 15, Nile Nubian = 9, and others = 21) using a polymerase chain reaction with sequence-specific primers method.

RESULTS

Susceptibility to RA was associated with a high frequency of DRB1*04 (P = 0.04), DRB1*10 (P = 0.04), and DQB1*03 (P = 2.2 x 10-8/Pc = 6.6 x 10-8) between study ethnic groups, while protective effects were shown with DRB1*07 (P = 0.01), DQB1*02 (P = 0.02), and DQB1*06 (P = 2.2 x 10-6/Pc = 6.6 x 10-6), with an inconsistent frequency between study ethnic groups. The HLA haplotypes that were high in frequency among RA ethnic groups and showed susceptibility associations were DRB1*03-DQB1*03, DRB1*04-DQB1*03, DRB1*08-DQB1*03, DRB1*13-DQB1*02, and DRB1*13-DQB1*03 (P = 0.00003/Pc = 0.0003, P = 0.0001/Pc = 0.0001, P = 0.03, P = 0.004/Pc = 0.03, and P = 3.79x10-8/Pc = 3.3x10-9, respectively). On the contrary, DRB1*03-DQB1*02, DRB1*07-DQB1*02, and DRB1*13-DQB1*06 were lower in frequency in the ethnic groups with RA and may confer protection (P = 0.004/Pc = 0.032, P = 0.002/Pc = 0.02, and P = 0.01, respectively).

CONCLUSIONS

Our findings indicate an association between HLA-DRB1 and DQB1 genotypes and the susceptibility to RA in the Sudanese population, with a moderate frequency between our ethnic groups.

Association of Human Leukocyte Antigen (HLA) class II (DRB1 and DQB1) alleles and haplotypes with Rheumatoid Arthritis in Sudanese patients

The aim of this study was to determine the Human Leukocyte Antigen (HLA) class II (DRB1 and DQB1) alleles and haplotype frequency in Rheumatoid Arthritis (RA) in the Sudanese population. The frequency of HLA-DRB1 and -DQB1 alleles and DRB1-DQB1 haplotypes were determined in 122 RA patients and 100 controls. HLA alleles were genotyped by the polymerase chain reaction-sequence specific primers (PCR-SSP) method. In RA patients, HLA-DRB1*04 and *10 alleles were high in frequency (9.6% vs 14.2%, P = 0.038 and P = 0.042, respectively), and dependently on anti-citrullinated protein antibodies (ACPAs) seropositivity (P = 0.044 and P = 0.027, respectively). In contrast, the frequency of the HLA-DRB1*07 allele was significantly low in patients than in controls (11.7% vs 5.0%, P = 0.010). Moreover, the HLA-DQB1*03 allele was strongly associated with RA risk (42.2%, P = 2.2x10^-8), whereas, HLA-DQB1*02 and *06 showed protective effects against RA (23.1% and 42.2%, P = 0.024 and P = 2.2x10^-6, respectively). Five different HLA haplotypes, DRB1*03-DQB1*03 (P = 0.00003), DRB1*04-DQB1*03 (P = 0.00014), DRB1*08-DQB1*03 (P = 0.027), DRB1*13-DQB1*02 (P = 0.004), and DRB1*13-DQB1*03 (P = 3.79x10^-8) were significantly associated with RA risk, while 3 protective haplotypes, DRB1*03-DQB1*02 (P_c = 0.008), DRB1*07-DQB1*02 (P_c = 0.004), and DRB1*13-DQB1*06 (P_c = 0.02) were identified. This is the first study determining the association between HLA class II alleles and haplotypes and RA risk in our population.

Reactivity of Rheumatoid Arthritis-Associated Citrulline-Dependent Antibodies to Epstein-Barr Virus Nuclear Antigen1-3

Rheumatoid arthritis (RA) is a chronic disease which causes joint inflammation and, ultimately, erosion of the underlying bone. Diagnosis of RA is based on the presence of biomarkers, such as anti-citrullinated protein antibodies (ACPA) and rheumatoid factors, along with clinical symptoms. Much evidence points to a link between the Epstein-Barr virus and RA. In this study, we analyzed ACPA reactivity to citrullinated peptides originating from Epstein-Barr nuclear antigens (EBNA1, EBNA2, and EBNA3) in order to elaborate the diagnostic potential of citrullinated EBNA peptides. Moreover, ACPA cross-reactivity to citrullinated peptides from myelin basic protein (MBP) was analyzed, as citrullinated MBP recently was described to be associated with multiple sclerosis, and some degree of sequence homology between MBP and citrullinated EBNA exists. A peptide from EBNA2, (EBNA2-A, GQGRGRWRG-Cit-GSKGRGRMH) reacted with approximately 70% of all RA sera, whereas only limited reactivity was detected to EBNA1 and EBNA3 peptides. Moreover, screening of ACPA reactivity to hybrid peptides of EBNA3-A (EPDSRDQQS-Cit-GQRRGDENRG) and EBNA2-A and peptides containing citrulline close to the N-terminal confirmed that ACPA sera contain different populations of ACPAs. No notable ACPA reactivity to MBP peptides was found, confirming that ACPAs are specific for RA, and that other factors than the presence of a central Cit-Gly motif are crucial for antibody binding. Collectively, these findings illustrate that citrullinated EBNA2 is an optimal candidate for ACPA detection, supporting current evidence that EBV is linked to RA onset.

Association of rheumatoid arthritis and its severity with human leukocytic antigen-DRB1 alleles in Kurdish region in North of Iraq

BACKGROUND

Rheumatoid arthritis is a complex multifactorial chronic disease, the importance of human leukocytic antigen (HLA) as a major genetic risk factor for rheumatoid arthritis was studied worldwide. The objective of this study is to identify the association of HLA-DRB1 subtypes with rheumatoid arthritis and its severity in Kurdish region.

METHODS

A case-control study recruited 65 rheumatoid arthritis patients and 100 healthy individuals as control group all over the Kurdistan region/Iraq. Both patient and control groups are genotyped using polymerase chain reaction with sequence specific primer. Anti-CCP antibodies were measured by ELISA test. Rheumatoid factor, C-reactive protein, and disease activity score 28 which measured by DAS-28 values were calculated. The DAS-28 was used to assess the clinical severity of the patients.

RESULTS

HLA-DRB1-0404 and HLA-DRB1-0405 frequencies showed a strong association with disease susceptibility (P < 0.001). The frequency of HLA-DRB1-0411 and HLA-DRB1-0413 were significantly higher in control group (P < 0.001). The frequency of rheumatoid factor and Anti-CCP were significantly higher among shared epitope-positive patients compared to shared epitope-negative patients (P < 0.001). Regarding the disease activity by DAS-28, rheumatoid arthritis patients didn't show significant difference between the shared epitope-positive and shared epitope-negative patients.

CONCLUSIONS

HLA-DR0404 and HLA-DR0405 alleles are related to RA, while HLA-DR1-0411 and HLA-DRB1-0413 protect against RA in the Kurdistan region in the North of Iraq.

Anti-carbamylated protein and peptide antibodies as potential inflammatory joint biomarkers in the relatives of rheumatoid arthritis patients

OBJECTIVE

Antibodies against carbamylated proteins/peptide (CarP) have been associated with severity in rheumatoid arthritis (RA) patients. However, their role in risk groups, specific targets and relation with periodontal disease (PD) is uncertain yet. The aim of this study was evaluated the association between the levels of anti-CarP with clinical manifestation, human leukocyte antigen (HLA) alleles, periodontal activity markers, PD diagnosis, PD severity, and presence of Porphyromonas gingivalis (P gingivalis) in relatives of patients with RA.

METHODS

One hundred and twenty-four individuals with a family history of RA in first-degree relatives (FDR) and 124 healthy individuals gender- and age-matched, RA activity was assessed. Antibodies against carbamylated protein anti-FCS-Carp and 2 carbamylated peptides of fibrinogen were selected (anti-Ca-Fib2, anti-Ca-Fib3).

RESULTS

Anti-FCS-Carp-positive, anti-Ca-Fib2 and anti-Ca-Fib3 were more frequent in FDR than controls (25.0% vs 14.5%, 34.7% vs 15.3% and 33.1% vs 11.3%, respectively). Anti-FCS-CarP were associated with the HLA-DRB1-SE* 1402 allele (P = .035) and highly sensitive C-reactive protein levels (P = .016), the anti-Ca-Fib2 antibodies were associated with the HLA-DRB1-SE* 1501 allele (P = .03), with non-SE* 0901 allele (P = .01), the anti-Ca-Fib3 was associated with positive rheumatoid factor (P = .0012). The FDR condition was associated with the presence of anti-Ca-Fib3 (odds ratio [OR] =4.7; 95% CI = 1.8-11.7; P = .001) and painful joints (OR = 2.2; 95% CI = 1.01-4.68; P = .045); we also detected an important trend toward the presence of P gingivalis (OR = 1.9; 95% CI = 0.9-3.7; P = .062).

CONCLUSION

The presence of anti-FCS-Carp, anti-Ca-Fib3 and anti-Ca-Fib2 antibodies may have a role for these antibodies as early biomarkers in the development of RA, probably including additional mechanisms related with other non-SE alleles; the anti-peptide antibodies proposed in the present study may represent a simpler way to identify antibodies directed to a specific target.

Methotrexate pharmacogenetics in the treatment of rheumatoid arthritis

For many decades, methotrexate (MXT) has remained the drug of choice in the treatment of rheumatoid arthritis (RA). Unfortunately, a considerable number of patients do not achieve an appropriate therapeutic response. Pharmacogenetics studies do not give usable results regarding differences in MTX response among RA patients. The mechanism of MTX action in RA is not completely understood. We present and discuss data regarding the molecular basis of folate and adenosine pathways, the most obvious MTX targets, to explain possible causes of therapy failure. The molecular basis of the disease could also have an impact on therapy outcomes and in this review we explore this. Finally, we make a short review of available pharmacogenetics study results.

Exploration of shared genetic susceptibility loci between type 1 diabetes and rheumatoid arthritis in the Pakistani population

OBJECTIVE

Type 1 diabetes (T1D) and rheumatoid arthritis (RA) are autoimmune diseases. It is known that certain genetic loci and factors that increase the overall autoimmunity risk can be shared among different autoimmune diseases. We sought to replicate seven T1D-related SNPs (single nucleotide polymorphisms) that have been previously reported to be associated with RA susceptibility in a small set of mixed family-based and case-control Pakistani sample in a relatively large and independent RA case-control sample from the same population. Seven T1D-associated SNPs (GLIS3/rs7020673, BACH2/rs11755527, SKAP2/rs7804356, GDSMB/rs2290400, C6orf173/rs9388489, LOC399716/rs947474 and DLK1-MEG2/rs941576) were genotyped in a large Pakistani RA case-control sample (n = 1959) using TaqMan^® SNP genotyping assays.

RESULTS

None of the tested SNPs showed statistically significant association with RA susceptibility; however, one SNP (GLIS3/rs7020673) showed a trend for association (OR = 0.88, p = 7.99E-02). Our study has failed to replicate the previously reported association of seven T1D-associated SNPs with RA risk in a large sample from the same population. Thus, our results do not support a major role of these T1D SNPs in affecting RA susceptibility in the Pakistani population.

Genetic analysis of the relation between IL2RA/IL2RB and rheumatoid arthritis risk

Background

The biological mechanisms driving disease chronicity in rheumatoid arthritis (RA) are largely unidentified. Therefore, we aimed to determine genetic risk factors for RA.

Methods

In this case–control study, which includes samples from 499 patients and 507 healthy controls, six single‐nucleotide polymorphisms (SNPs) in interleukin‐2 receptor subunit alpha (IL2RA) and IL2RB were selected. Genotyping was performed using the Agena MassARRAY platform, and the statistical analyses were performed using the chi‐squared and Fisher's exact tests, genetic model analysis, and haplotype analysis.

Result

In the allele model, using the chi‐squared test, the result showed that rs791588 in IL2RA was associated with a decreased RA risk (odds ratios [OR] = 0.74, 95% confidence intervals [CI] = 0.62–0.89, p = 0.0014) after adjusting for age and gender. In the genetic model, logistic regression analyses revealed that rs791588 was associated with a decreased risk of RA under the codominant model, dominant model, recessive model, and log‐additive model. Stratification analysis revealed that two SNPs (rs791588 and rs2281089) were significantly associated with a reduced RA risk in an allele and genetic model after stratification by gender or age (p < 0.05). In addition, the haplotypes “C_rs12569923G_rs791588” and “C_rs12569923T_rs791588” of IL2RA was associated with an increased risk of RA adjusted by age and gender (OR = 1.35, 95% CI: 1.12–1.64, p = 0.0016; OR = 1.24, 95% CI: 1.03–1.48, p = 0.021).

Conclusion

This finding indicates that the inherited altered genetic constitution at IL2RA may predispose to a less destructive course of RA.

Gene expression analysis of vascular pathophysiology related to anti-TNF treatment in rheumatoid arthritis

OBJECTIVES

Impaired vascular pathophysiology and increased cardiovascular (CV) mortality are associated with rheumatoid arthritis (RA). To date, no genomic analysis of RA- and RA treatment-related vascular pathophysiology has been published. In this pilot study, we performed gene expression profiling in association with vascular pathophysiology in RA patients.

METHODS

Sixteen and 19 biologic-naïve RA patients were included in study 1 and study 2, respectively. In study 1, genetic signatures determined by microarray were related to flow-mediated vasodilation (FMD), pulse-wave velocity (PWV), and common carotid intima-media thickness (IMT) of patients. In study 2, clinical response (cR) vs non-response (cNR) to 1-year etanercept (ETN) or certolizumab pegol (CZP) treatment, as well as "vascular" response (vR) vs non-response (vNR) to biologics, were also associated with genomic profiles. Multiple testing could not be performed due to the relatively small number of patients; therefore, our pilot study may lack power.

RESULTS

In study 1, multiple genes were up- or downregulated in patients with abnormal vs normal FMD, IMT, and PWV. In study 2, there were 13 cR and 6 cNR anti-tumor necrosis factor (TNF)-treated patients. In addition, 10, 9, and 8 patients were FMD-20%, IMT-20%, and PWV-20% responders. Again, vascular responder status was associated with changes of the expression of various genes. The highest number of genes showing significant enrichment were involved in positive regulation of immune effector process, regulation of glucose transport, and Golgi vesicle budding.

CONCLUSION

Differential expression of multiple genetic profiles may be associated with vascular pathophysiology associated with RA. Moreover, distinct genetic signatures may also be associated with clinical and vascular responses to 1-year anti-TNF treatment.

Genetic implications in the pathogenesis of rheumatoid arthritis; an updated review

Three important factors, including genetics, environment factors and autoimmunity play a role in the pathogenesis of rheumatoid arthritis (RA). The heritability of RA has been accounted to be 50-60%, while the HLA involvement in heritability of the disease has been accounted to be 10-40%. It has been documented that shared epitope (SE) alleles, such as HLA-DRB1*01 and DRB1*04, some HLA alleles like HLA-DRB1*13 and DRB1*15 are connected to RA susceptibility. An advanced classification of SE categorizes SE alleles into four main groups namely, S1, S2, S3D, and S3P. The S2 and S3P groups have been linked to susceptibility of seropositive RA. Various genome-wide association studies (GWAS) have discovered many susceptibility loci implicated in pathogenesis of RA. Some of the important single nucleotide polymorphisms (SNPs) linked to RA are TRAF1, STAT4, CTLA4, IRF5, CCR6, PTPN22, IL23R, and PADI4. HLA and non-HLA genes may discriminate anti-cyclic citrullinated peptide (anti-CCP) antibody-positive and anti-CCP-negative RA groups. Furthermore, risk of the disease has also been linked to environmental agents, mainly cigarette smoking. Pharmacogenomics has also confirmed SNPs or genetic patterns that might be linked to drugs responses. Different aspects of genetic involvement in the pathogenesis, etiology, and RA complications are reviewed in this article.

Genetic markers as therapeutic target in rheumatoid arthritis: A game changer in clinical therapy?

Rheumatoid arthritis (RA) is a chronic, inflammatory, multi-systemic autoimmune disease unremitted by genetic and environmental factors. The factors are crucial but inadequate in the development of disease; however, these factors can be representative of potential therapeutic targets and response to clinical therapy. Insights into the contribution of genetic risk factors are currently in progress with studies querying the genetic variation, their role in gene expression of coding and non-coding genes and other mechanisms of disease. In this review, we describe the significance of genetic markers architecture of RA through genome-wide association studies and meta-analysis studies. Further, it also reveals the mechanism of disease pathogenesis investigated through the mutual findings of functional and genetic studies of individual RA-associated genes, which includes HLA-DRB1, HLA-DQB1, HLA-DPB1, PADI4, PTPN22, TRAF1-C5, STAT4 and C5orf30. However, the genetic background of RA remains to be clearly depicted. Prospective efforts of the post-genomic and functional genomic period can travel toward real possible assessment of the genetic effect on RA. The discovery of novel genes associated with the disease can be appropriate in identifying potential biomarkers, which could assist in early diagnosis and aggressive treatment.

Rheumatoid arthritis onset in postmenopausal women: Does the ACPA seropositive subset result from genetic effects, estrogen deficiency, skewed profile of CD4(+) T-cells, and their interactions?

Rheumatoid arthritis (RA) incidence displays a differentiated age-dependent female-to-male ratio in which women outnumber men. Evidence that the peak incidence of RA in women coincides with menopause age, suggests a potential estrogenic role to disease etiology. Estrogens exert physiologically both stimulatory and inhibitory effects on the immune system. Epidemiologic and animal model studies with estrogen deprivation or supplementation suggested estrogens as to play, mainly, a protective role in RA immunopathology. In this review, we propose that some yet unidentified disturbances associated with estrogen circulating levels, differentiated by the menopausal status, play a major role in women's RA susceptibility. We focus on the interaction between estrogen deprivation and genetic risk alleles for anti-citrullinated protein antibodies (ACPA) seropositive RA, as a major driving force for increased immune reactivity and RA susceptibility, in postmenopausal women. This opens up new fields for research concerning the association among different irregular estrogenic conditions, the cytokine milieu, and age/menopausal status bias in RA.

Family history of rheumatoid arthritis: an old concept with new developments

Family history of rheumatoid arthritis (RA) is a proxy for an individual's genetic and, in part, environmental risk of developing RA, and is a well-recognized predictor of disease onset. Although family history of RA is an old concept, the degree of familial aggregation of RA, whether it differs by age, sex, or serology, and what value it has for clinical decisions once a diagnosis of RA has been made remain unclear. New data have been emerging in parallel to substantial progress made in genetic association studies. In this Review, we describe the various ways that familial aggregation has been measured, and how the findings from these studies, whether they are based on twins, cohorts of first-degree relatives, or genetic data, correspond to each other and aid understanding of the aetiology of RA. In addition, we review the potential usefulness of family history of RA from a clinical point of view, demonstrating that, in the era of big data and genomics, family history still has a role in directing clinical decision-making and research.

Lower omega-3 fatty acids are associated with the presence of anti-cyclic citrullinated peptide autoantibodies in a population at risk for future rheumatoid arthritis: a nested case-control study

OBJECTIVE

The aim of this study was to investigate omega-3 fatty acid (FA) supplement use and omega-3 FAs in erythrocyte membranes [omega-3 FA % in erythrocyte membranes (RBC)] and their association with anti-CCP autoantibodies in a population without RA, but who are at genetic risk for RA.

METHODS

The multicentre Studies of the Etiology of RA (SERA) cohort includes RA-free subjects who are first-degree relatives of RA probands or are enriched with the HLA-DR4 allele. In a nested case-control study, 30 SERA cases were identified who were anti-CCP2 antibody positive. We further identified 47 autoantibody negative controls, frequency matched to cases on age at study visit, sex, race and study site. Anti-CCP2 status, self-reported omega-3 FA supplement use and omega-3 FA % in RBCs were obtained from a single visit.

RESULTS

Anti-CCP2 positive cases were less likely than controls to report omega-3 FA supplement use (odds ratio: 0.14; 95% CI 0.03, 0.68). In addition, the likelihood of anti-CCP2 positivity was inversely associated with total omega-3 FA % in RBCs (odds ratio: 0.47; 95% CI 0.24, 0.92, for a s.d. increase).

CONCLUSION

The inverse association between anti-CCP2 positivity and self-reported omega-3 FA supplement use and omega-3 FA % in RBCs suggests that omega-3 FAs may protect against the development of RA-related autoimmunity in pre-clinical RA.

Genetic link of type 1 diabetes susceptibility loci with rheumatoid arthritis in Pakistani patients

Rheumatoid arthritis (RA) and type 1 diabetes (T1D) are two autoimmune disorders that have been reported to co-occur in the same subjects or in different subjects from the same family. This suggests the sharing of disease susceptibility loci between RA and T1D. This study was aimed to find out such susceptibility loci that are common in both T1D and RA in Pakistani population. A total of 366 Pakistanis comprising related and unrelated RA cases and controls were recruited. Blood samples were collected from all patients followed by DNA isolation. Thirty-one single-nucleotide polymorphisms (SNPs) previously reported to be associated with T1D were genotyped in RA cases and controls using TaqMan SNP genotyping assays. Data was analyzed using FamCC software. We have identified seven SNP associations that survived multiple testing corrections using false discovery rate: SKAP2/rs7804356 (p = 2.47E-04), GLIS3/rs7020673 (p = 2.86E-04), GSDMB/rs2290400 (p = 23.48E-04), BACH2/rs11755527 (p = 9.16E-04), C6orf173/ rs9388489 (p = 3.11E-03), PRKCQ/DKFZp667F0711/ rs947474 (p = 4.53E-03), and DLK1/ rs941576 (p = 9.51E-03). Our results support the presence of overlapping loci between RA and T1D in Pakistani patients.

Association of IL-18 promoter gene polymorphisms with rheumatoid arthritis: a meta-analysis

Interleukin-18(IL-18) plays a potential pathological role in rheumatoid arthritis (RA). The conclusions of the published reports on the relationship between single-nucleotide polymorphisms -607C/A (rs1946518) and -137G/C (rs187238) located in the IL-18 gene promoter and RA risk remain controversial. This meta-analysis was performed to evaluate the association between IL-18 gene promoter (-607A/C and -137C/G) polymorphisms and RA using (1) allele, (2) codominant, (3) dominant, and (4) recessive models. Literature search was conducted up to January, 2013, in PubMed, EMBASE, Spring-link, Web of Science, Wanfang (Chinese) and China National Knowledge Infrastructure (CNKI). A total of 10 studies from eight articles involving 2,662 cases and 2,168 controls for -607A/C polymorphism and 9 studies from six articles involving 1,331 cases and 1,468 controls for -137C/G polymorphism were considered in the meta-analysis. For the relationship of IL-18 -607A/C polymorphism with RA risk, significant association was observed in allele model (OR = 0.778, 95 % CI = 0.633-0.955) and dominant model (OR = 0.618, 95 % CI = 0.466-0.819). However, no significant association could be observed between -137C/G polymorphism and RA risk under all genetic models (allele model: OR = 0.940, 95 % CI = 0.777-1.138; codominant model: OR = 1.079, 95 % CI = 0.574-2.029; dominant model: OR = 0.913, 95 % CI = 0.779-1.069; recessive model: OR = 1.133, 95 % CI = 0.586-2.190). In the subgroup analysis by ethnicity, significant result was also found in Asian populations but not found in Caucasian populations for the relationship of IL-18 -607A/C polymorphism with RA risk; while no obvious association was found between IL-18 -137C/G polymorphism and RA risk. This meta-analysis indicates that IL-18 -607A/C polymorphism in promoter region may be associated with RA risk.

Genetics of rheumatoid arthritis - a comprehensive review

The "Bermuda triangle" of genetics, environment and autoimmunity is involved in the pathogenesis of rheumatoid arthritis (RA). Various aspects of genetic contribution to the etiology, pathogenesis and outcome of RA are discussed in this review. The heritability of RA has been estimated to be about 60 %, while the contribution of HLA to heritability has been estimated to be 11-37 %. Apart from known shared epitope (SE) alleles, such as HLA-DRB1*01 and DRB1*04, other HLA alleles, such as HLA-DRB1*13 and DRB1*15 have been linked to RA susceptibility. A novel SE classification divides SE alleles into S1, S2, S3P and S3D groups, where primarily S2 and S3P groups have been associated with predisposition to seropositive RA. The most relevant non-HLA gene single nucleotide polymorphisms (SNPs) associated with RA include PTPN22, IL23R, TRAF1, CTLA4, IRF5, STAT4, CCR6, PADI4. Large genome-wide association studies (GWAS) have identified more than 30 loci involved in RA pathogenesis. HLA and some non-HLA genes may differentiate between anti-citrullinated protein antibody (ACPA) seropositive and seronegative RA. Genetic susceptibility has also been associated with environmental factors, primarily smoking. Some GWAS studies carried out in rodent models of arthritis have confirmed the role of human genes. For example, in the collagen-induced (CIA) and proteoglycan-induced arthritis (PgIA) models, two important loci - Pgia26/Cia5 and Pgia2/Cia2/Cia3, corresponding the human PTPN22/CD2 and TRAF1/C5 loci, respectively - have been identified. Finally, pharmacogenomics identified SNPs or multiple genetic signatures that may be associated with responses to traditional disease-modifying drugs and biologics.

Of mice and men: how animal models advance our understanding of T-cell function in RA

The involvement of autoreactive T cells in the pathogenesis of rheumatoid arthritis (RA) as well as in autoimmune animal models of arthritis has been well established; however, unanswered questions, such as the role of joint-homing T cells, remain. Animal models of arthritis are superb experimental tools in demonstrating how T cells trigger joint inflammation, and thus can help to further our knowledge of disease mechanisms and potential therapies. In this Review, we discuss the similarities and differences in T-cell subsets and functions between RA and mouse arthritis models. For example, various T-cell subsets are involved in both human and mouse arthritis, but differences might exist in the cytokine regulation and plasticity of these cells. With regard to joint-homing T cells, an abundance of synovial T cells is present in humans compared with mice. On the other hand, local expansion of type 17 T-helper (TH17) cells is observed in some animal models, but not in RA. Finally, whereas T-cell depletion therapy essentially failed in RA, antibody targeting of T cells can work, at least preventatively, in most arthritis models. Clearly, additional human and animal studies are needed to fill the gap in our understanding of the specific contribution of T-cell subsets to arthritis in mice and men.

Familial risks and heritability of rheumatoid arthritis: role of rheumatoid factor/anti-citrullinated protein antibody status, number and type of affected relatives, sex, and age

OBJECTIVE

To estimate familial aggregation of rheumatoid arthritis (RA) in 3 large population-representative samples and to test if familial aggregation is affected by rheumatoid factor (RF)/anti-citrullinated protein antibody (ACPA) status, type of relative, sex, and age at onset of RA.

METHODS

A register-based nested case-control study was performed in the Swedish total population. Data on patients with RA were ascertained through the nationwide Swedish Patient Register (n = 88,639), the clinical Swedish Rheumatology Quality Register (n = 11,519), and the Epidemiological Investigation of Rheumatoid Arthritis case-control study (n = 2,871). Data on first- and second-degree relatives were obtained through the Swedish Multigeneration Register. Familial risks were calculated using conditional logistic regression.

RESULTS

Consistent across data sources, the familial odds ratio for RA was ∼3 in first-degree relatives of RA patients and 2 in second-degree relatives. Familial risks were similar among siblings, parents, and offspring. Familial aggregation was not modified by sex, but was higher in RA patients with early-onset disease and in RF/ACPA-positive RA patients. The observed familial risks were consistent with a heritability of ∼50% for ACPA-positive RA and ∼20% for ACPA-negative RA.

CONCLUSION

The pattern of risks suggests that familial factors influence RA in men and women equally and that these factors are of less importance for late-onset RA. Familial factors are more important for seropositive RA, but there is significant familial overlap between seropositive RA and seronegative RA. Even if the familial risk is assumed to be completely due to genetics, the observed risks suggest that heritability of RA is lower than previously reported, in particular for ACPA-negative RA.

The rs3768777-G allele of ITGAV gene is associated with rheumatoid arthritis

Integrin αvβ3 (vitronectin receptor) plays a prominent role in angiogenesis, a key pathogenic feature of rheumatoid arthritis (RA). Moreover, integrin αV (ITGAV) subunit gene has been associated with a susceptibility to RA. The aim of the present study was to detect the potential association between ITGAV gene polymorphisms and a susceptibility to RA in a Turkish cohort. DNA samples were harvested from 160 patients with RA and 144 healthy controls (HC). Three single-nucleotide polymorphisms of ITGAV gene (rs3738919, rs3768777, and rs10174098) were genotyped using real-time PCR. Serum vitronectin levels were analyzed in 30 RA patients, 28 Behçet's disease (BD) patients, and 30 HC subjects. There was no significant difference between the RA and HC groups in terms of the genotypic and allelic distributions of rs3738919 and rs10174098 polymorphisms. However, the prevalence of rs3768777-G allele was higher in the RA group than in the HC group (OR 2.3, 95 % CI 1.6-3.2, p < 0.0001). Moreover, there was a significant association between RA and the genotypic distribution of rs3768777 (GG + AG vs. AA: OR 2.1, 95 % CI 1.3-3.4; GG vs. AG + AA: OR 4.1, 95 % CI 2.1-7.8). Serum vitronectin levels were lower in the RA and BD groups than in the HC group (p ANOVA = 0.002). The rs3738919 and rs10174098 polymorphisms of the ITGAV gene seem not to be associated with susceptibility to RA in Turkish patients. However, rs3768777 increases the risk of RA in this group. These results suggest that the ITGAV gene may be a candidate gene for the etiopathogenesis of RA.

Measles contributes to rheumatoid arthritis: evidence from pathway and network analyses of genome-wide association studies

Growing evidence from epidemiological studies indicates the association between rheumatoid arthritis (RA) and measles. However, the exact mechanism for this association is still unclear now. We consider that the strong association between both diseases may be caused by shared genetic pathways. We performed a pathway analysis of large-scale RA genome-wide association studies (GWAS) dataset with 5,539 cases and 20,169 controls of European descent. Meanwhile, we evaluated our findings using previously identified RA loci, protein-protein interaction network and previous results from pathway analysis of RA and other autoimmune diseases GWAS. We confirmed four pathways including Cytokine-cytokine receptor interaction, Jak-STAT signaling, T cell receptor signaling and Cell adhesion molecules. Meanwhile, we highlighted for the first time the involvement of Measles and Intestinal immune network for IgA production pathways in RA. Our results may explain the strong association between RA and measles, which may be caused by the shared genetic pathway. We believe that our results will be helpful for future genetic studies in RA pathogenesis and may significantly assist in the development of therapeutic strategies.

Genetics and epigenetics of rheumatoid arthritis

Investigators have made key advances in rheumatoid arthritis (RA) genetics in the past 10 years. Although genetic studies have had limited influence on clinical practice and drug discovery, they are currently generating testable hypotheses to explain disease pathogenesis. Firstly, we review here the major advances in identifying RA genetic susceptibility markers both within and outside of the MHC. Understanding how genetic variants translate into pathogenic mechanisms and ultimately into phenotypes remains a mystery for most of the polymorphisms that confer susceptibility to RA, but functional data are emerging. Interplay between environmental and genetic factors is poorly understood and in need of further investigation. Secondly, we review current knowledge of the role of epigenetics in RA susceptibility. Differences in the epigenome could represent one of the ways in which environmental exposures translate into phenotypic outcomes. The best understood epigenetic phenomena include post-translational histone modifications and DNA methylation events, both of which have critical roles in gene regulation. Epigenetic studies in RA represent a new area of research with the potential to answer unsolved questions.

Non-MHC risk alleles in rheumatoid arthritis and in the syntenic chromosome regions of corresponding animal models

Rheumatoid arthritis (RA) is a polygenic autoimmune disease primarily affecting the synovial joints. Numerous animal models show similarities to RA in humans; some of them not only mimic the clinical phenotypes but also demonstrate the involvement of homologous genomic regions in RA. This paper compares corresponding non-MHC genomic regions identified in rodent and human genome-wide association studies (GWAS). To date, over 30 non-MHC RA-associated loci have been identified in humans, and over 100 arthritis-associated loci have been identified in rodent models of RA. The genomic regions associated with the disease are designated by the name(s) of the gene having the most frequent and consistent RA-associated SNPs or a function suggesting their involvement in inflammatory or autoimmune processes. Animal studies on rats and mice preferentially have used single sequence length polymorphism (SSLP) markers to identify disease-associated qualitative and quantitative trait loci (QTLs) in the genome of F2 hybrids of arthritis-susceptible and arthritis-resistant rodent strains. Mouse GWAS appear to be far ahead of rat studies, and significantly more mouse QTLs correspond to human RA risk alleles.

Prostaglandins and rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, autoimmune, and complex inflammatory disease leading to bone and cartilage destruction, whose cause remains obscure. Accumulation of genetic susceptibility, environmental factors, and dysregulated immune responses are necessary for mounting this self-reacting disease. Inflamed joints are infiltrated by a heterogeneous population of cellular and soluble mediators of the immune system, such as T cells, B cells, macrophages, cytokines, and prostaglandins (PGs). Prostaglandins are lipid inflammatory mediators derived from the arachidonic acid by multienzymatic reactions. They both sustain homeostatic mechanisms and mediate pathogenic processes, including the inflammatory reaction. They play both beneficial and harmful roles during inflammation, according to their site of action and the etiology of the inflammatory response. With respect to the role of PGs in inflammation, they can be effective mediators in the pathophysiology of RA. Thus the use of agonists or antagonists of PG receptors may be considered as a new therapeutic protocol in RA. In this paper, we try to elucidate the role of PGs in the immunopathology of RA.

A knowledge-based method for association studies on complex diseases

Complex disorders are a class of diseases whose phenotypic variance is caused by the interplay of multiple genetic and environmental factors. Analyzing the complexity underlying the genetic architecture of such traits may help develop more efficient diagnostic tests and therapeutic protocols. Despite the continuous advances in revealing the genetic basis of many of complex diseases using genome-wide association studies (GWAS), a major proportion of their genetic variance has remained unexplained, in part because GWAS are unable to reliably detect small individual risk contributions and to capture the underlying genetic heterogeneity. In this paper we describe a hypothesis-based method to analyze the association between multiple genetic factors and a complex phenotype. Starting from sets of markers selected based on preexisting biomedical knowledge, our method generates multi-marker models relevant to the biological process underlying a complex trait for which genotype data is available. We tested the applicability of our method using the WTCCC case-control dataset. Analyzing a number of biological pathways, the method was able to identify several immune system related multi-SNP models significantly associated with Rheumatoid Arthritis (RA) and Crohn's disease (CD). RA-associated multi-SNP models were also replicated in an independent case-control dataset. The method we present provides a framework for capturing joint contributions of genetic factors to complex traits. In contrast to hypothesis-free approaches, its results can be given a direct biological interpretation. The replicated multi-SNP models generated by our analysis may serve as a predictor to estimate the risk of RA development in individuals of Caucasian ancestry.

Genetics of rheumatoid arthritis: an impressionist perspective

Rheumatoid arthritis (RA) is the most common rheumatic disease. The genetic basis of RA is supported through the identification of more than 30 susceptibility genetic variants. Each of these genes individually makes only a slight contribution to the risk of disease. Moreover, there is significant disparity in the genetic variants associated with different RA subgroups and patient ethnicities, which emphasizes the intricate nature of the disease's pathogenesis, and the complexities involved in large-scale genetic studies. This review evaluates critically the recent literature on the genetic contribution to RA and assesses the methodology used to identify these risk alleles.

Associations between six classical HLA loci and rheumatoid arthritis: a comprehensive analysis

Although the HLA region contributes to one-third of the genetic factors affecting rheumatoid arthritis (RA), there are few reports on the association of the disease with any of the HLA loci other than the DRB1. In this study we examined the association between RA and the alleles of the six classical HLA loci including DRB1. Six HLA loci (HLA-A, -B, -C, -DRB1, -DQB1 and -DPB1) of 1659 Japanese subjects (622 cases; 488 anti-cyclic citrullinated peptides (CCP) antibody (Ab) positive (82.6%); 103 anti-CCP Ab negative (17.4%); 31 not known and 1037 controls) were genotyped. Disease types and positivity/negativity for CCP autoantibodies were used to stratify the cases. Statistical and genetic assessments were performed by Fisher's exact tests, odds ratio, trend tests and haplotype estimation. None of the HLA loci were significantly associated with CCP sero-negative cases after Bonferroni correction and we therefore limited further analyses to using only the anti CCP-positive RA cases and both anti-CCP positive and anti-CCP negative controls. Some alleles of the non-DRB1 HLA loci showed significant association with RA, which could be explained by linkage disequilibrium with DRB1 alleles. However, DPB1*02:01, DPB1*04:01 and DPB1*09:01 conferred RA risk/protection independently from DRB1. DPB1*02:01 was significantly associated with the highly erosive disease type. The odds ratio of the four HLA-loci haplotypes with DRB1*04:05 and DQB1*04:01, which were the high-risk HLA alleles in Japanese, varied from 1.01 to 5.58. C*07:04, and B*15:18 showed similar P-values and odds ratios to DRB1*04:01, which was located on the same haplotype. This haplotype analysis showed that the DRB1 gene as well as five other HLA loci is required for a more comprehensive understanding of the genetic association between HLA and RA than analyzing DRB1 alone.

Novel regulatory mechanisms in inflammatory arthritis: a role for microRNA

Elucidating pathways that regulate cytokine production in the context of autoimmune disease will likely lead to the development of novel therapeutics. Herein, we review data suggesting that microRNAs (miRs) represent one such level of regulatory activity, with particular emphasis on the pathogenesis of rheumatoid arthritis (RA). A series of miRs have been identified to be dysregulated in cell subsets within the articular compartment of patients with RA. These have a critical role in regulating cartilage-invading phenotype of RA synovial fibroblasts. More recently, several studies suggest that miRs also regulate leukocyte activation and cytokine production that in turn contribute to the immunologic component of effector synovial pathology. Together, these observations open an exciting new vista of understanding and therapeutic opportunity for this difficult and common disease.