Dense genome-wide linkage analysis of rheumatoid arthritis, including covariates

Dissecting the Role of NF-κb Protein Family and Its Regulators in Rheumatoid Arthritis Using Weighted Gene Co-Expression Network

Rheumatoid arthritis (RA) is a chronic synovial autoinflammatory disease that destructs the cartilage and bone, leading to disability. The functional regulation of major immunity-related pathways like nuclear factor kappa B (NF-κB), which is involved in the chronic inflammatory reactions underlying the development of RA, remains to be explored. Therefore, this study has adopted statistical and knowledge-based systemic investigations (like gene correlation, semantic similarity, and topological parameters based on graph theory) to study the gene expression status of NF-κB protein family (NK^PF) and its regulators in synovial tissues to trace the molecular pathways through which these regulators contribute to RA. A complex protein–protein interaction map (PPIM) of 2,742 genes and 37,032 interactions was constructed from differentially expressed genes (p ≤ 0.05). PPIM was further decomposed into a Regulator Allied Protein Interaction Network (RA^PIN) based on the interaction between genes (5 NK^PF, 31 seeds, 131 hubs, and 652 bottlenecks). Pathway network analysis has shown the RA-specific disturbances in the functional connectivity between seed genes (RIPK1, ATG7, TLR4, TNFRSF1A, KPNA1, CFLAR, SNW1, FOSB, PARVA, CX3CL1, and TRPC6) and NK^PF members (RELA, RELB, NFKB2, and REL). Interestingly, these genes are known for their involvement in inflammation and immune system (signaling by interleukins, cytokine signaling in immune system, NOD-like receptor signaling, MAPK signaling, Toll-like receptor signaling, and TNF signaling) pathways connected to RA. This study, for the first time, reports that SNW1, along with other NK regulatory genes, plays an important role in RA pathogenesis and might act as potential biomarker for RA. Additionally, these genes might play important roles in RA pathogenesis, as well as facilitate the development of effective targeted therapies. Our integrative data analysis and network-based methods could accelerate the identification of novel drug targets for RA from high-throughput genomic data.

Extracts of Bauhinia championii (Benth.) Benth. attenuate the inflammatory response in a rat model of collagen-induced arthritis

Rheumatoid arthritis is considered a serious public health problem, which is commonly treated with traditional Chinese or herbal medicine. The present study evaluated the effects of Bauhinia championii (Benth.) Benth. extraction (BCBE) on a type II collagen-induced arthritis (CIA) rat model. Wistar rats with CIA received either 125 or 500 mg/kg BCBE, after which, paw swelling was markedly suppressed compared with in the model group. In addition, BCBE significantly ameliorated pathological joint alterations, including synovial hyperplasia, and cartilage and bone destruction. The protein and mRNA expression levels of interleukin (IL)-6, IL-8, tumor necrosis factor-α and nuclear factor-κB in synovial tissue were determined by immunohistochemical staining, western blot analysis and reverse transcription-polymerase chain reaction. The results demonstrated that the expression levels of these factors were significantly downregulated in the BCBE-treated group compared with in the model group. These results indicated that BCBE may exert an inhibitory effect on the CIA rat model, and its therapeutic potential is associated with its anti-inflammatory action.

Cellular adhesion gene SELP is associated with rheumatoid arthritis and displays differential allelic expression

In rheumatoid arthritis (RA), a key event is infiltration of inflammatory immune cells into the synovial lining, possibly aggravated by dysregulation of cellular adhesion molecules. Therefore, single nucleotide polymorphisms of 14 genes involved in cellular adhesion processes (CAST, ITGA4, ITGB1, ITGB2, PECAM1, PTEN, PTPN11, PTPRC, PXN, SELE, SELP, SRC, TYK2, and VCAM1) were analyzed for association with RA. Association analysis was performed consecutively in three European RA family sample groups (Nfamilies = 407). Additionally, we investigated differential allelic expression, a possible functional consequence of genetic variants. SELP (selectin P, CD62P) SNP-allele rs6136-T was associated with risk for RA in two RA family sample groups as well as in global analysis of all three groups (ptotal = 0.003). This allele was also expressed preferentially (p<10-6) with a two- fold average increase in regulated samples. Differential expression is supported by data from Genevar MuTHER (p1 = 0.004; p2 = 0.0177). Evidence for influence of rs6136 on transcription factor binding was also found in silico and in public datasets reporting in vitro data. In summary, we found SELP rs6136-T to be associated with RA and with increased expression of SELP mRNA. SELP is located on the surface of endothelial cells and crucial for recruitment, adhesion, and migration of inflammatory cells into the joint. Genetically determined increased SELP expression levels might thus be a novel additional risk factor for 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.

Vitamin D Receptor Polymorphism rs2228570 (Fok1) Is Associated with Rheumatoid Arthritis in North American Natives

Objective.

Vitamin D (VitD) has immunomodulatory activity relevant to rheumatoid arthritis (RA) and acts by binding nuclear receptors that regulate gene transcription. VitD receptor polymorphisms have been variably associated with RA. Because North American Native (NAN) populations have a high prevalence of RA with a strong genetic contribution, we studied potential associations of the rs2228570 (Fok1) VitD receptor polymorphism in a Canadian NAN population.

Methods.

The single-nucleotide polymorphism (SNP) Fok1 was tested by sequencing NAN patients with RA (n = 448) and unrelated NAN controls (n = 704). Associations were tested using genotypic, dominant, and recessive models.

Results.

The minor allele frequency (F/C) in the NAN control population was 0.44 and lower than reported in white subjects of the same geographical area. The Fok1 VitD receptor SNP was significantly associated with RA. Comparing patients with RA to unaffected NAN controls, the Fok1 SNP was associated with RA using both genotypic [FF vs Ff vs ff: RA 20%, 54%, 26% vs control 22%, 44%, 34% (chi-square 13.35, p = 0.003)] and dominant models [FF/Ff vs ff: RA 74% vs 26% control 66% vs 34% (OR 1.5, 95% CI 1.16–1.96, p = 0.003)]. This association was strongest in shared-epitope-positive RA.

Conclusion.

VitD receptor polymorphisms may contribute to the high prevalence of RA in NAN populations.

Disease-promoting and -protective genomic loci on mouse chromosomes 3 and 19 control the incidence and severity of autoimmune arthritis

Proteoglycan (PG)-induced arthritis (PGIA) is a murine model of rheumatoid arthritis. Arthritis-prone BALB/c mice are 100% susceptible, whereas the major histocompatibility complex-matched DBA/2 strain is completely resistant to PGIA. To reduce the size of the disease-suppressive loci for sequencing and to find causative genes of arthritis, we created a set of BALB/c.DBA/2-congenic/subcongenic strains carrying DBA/2 genomic intervals overlapping the entire Pgia26 locus on chromosome 3 (chr3) and Pgia23/Pgia12 loci on chr19 in the arthritis-susceptible BALB/c background. Upon immunization of these subcongenic strains and their wild-type (BALB/c) littermates, we identified a major Pgia26a sublocus on chr3 that suppressed disease onset, incidence and severity via controlling the complex trait of T-cell responses. The region was reduced to 3 Mbp (11.8 Mbp with flanking regions) in size and contained gene(s) influencing the production of a number of proinflammatory cytokines. Additionally, two independent loci (Pgia26b and Pgia26c) suppressed the clinical scores of arthritis. The Pgia23 locus (∼3 Mbp in size) on chr19 reduced arthritis susceptibility and onset, and the Pgia12 locus (6 Mbp) associated with low arthritis severity. Thus, we have reached the critical sizes of arthritis-associated genomic loci on mouse chr3 and chr19, which are ready for high-throughput sequencing of genomic DNA.

Genetic heterogeneity in rheumatoid arthritis mouse models induced by extrinsic and intrinsic factors

A cumulative effect of the susceptibility genes with polymorphic alleles may be responsible for rheumatoid arthritis (RA). The objective of this study was to clarify whether susceptibility to RA is under the control of common allelic loci between two different RA models induced by extrinsic and intrinsic factors, collagen-induced arthritis (CIA) in DBA/1 mice and arthritis in MRL/Mp (MRL) mice associated with the Fas deficient mutant gene, Fas(lpr), respectively. CIA was examined in mice of parental DBA/1 and MRL, (MRL x DBA/1) F1 and (MRL x DBA/1) F2 progenies. In genome-wide screening of the severity in the F2 using microsatellite markers, significant linkage was observed on chromosomes 5 and 17 at map position of D5Mit259 and H-2, respectively, associated with DBA/1 alleles, while there was no loci associated with arthritis of MRL-Fas(lpr) mice previously identified. In a quantitative trait locus (QTL) analysis, the locus on chromosome 5 showed the highest peak at map position 35 cM (LOD score 6.0). This study may indicate that the arthritis induced by extrinsic and intrinsic factors is under the control of a different combination of susceptibility genes with common and different alleles, possibly simulating the genetic heterogeneity of RA.

Update on peptidylarginine deiminases and deimination in skin physiology and severe human diseases

Deimination (or citrullination) is a recently described post-translational modification, but its consequences are not yet well understood. It is catalysed by peptidylarginine deiminases (PADs). These enzymes transform arginyl residues involved in a peptidyl link into citrullyl residues in a calcium-dependent manner. Several PAD substrates have already been identified like filaggrin and keratins K1 and K10 in the epidermis, trichohyalin in hair follicles, but also ubiquitous proteins like histones. PADs act in a large panel of physiological functions as cellular differentiation or gene regulation. It has been suggested that deimination plays a role in many major diseases such as rheumatoid arthritis, multiple sclerosis, Alzheimer's disease and psoriasis. Five human genes (PADIs), encoding five highly conserved paralogous enzymes (PAD1-4 and 6), have been characterized. These genes are clustered in a single locus, at 1p35-36 in man. Only PAD1-3 are expressed in human epidermis. PADs seem to be controlled at transcriptional, translational and activity levels and they present particular substrate specificities. In this review, we shall discuss these main biochemical, genetic and functional aspects of PADs together with their pathophysiological implications.

Anti-inflammatory effect of Sanshuibaihu decoction may be associated with nuclear factor-kappa B and p38 MAPK alpha in collagen-induced arthritis in rat

Sanshuibaihu decoction (SSBH) is an anti-arthritic Chinese herbal formula which has been used in the treatment of rheumatoid arthritis (RA) for many years. We herein aimed to confirm its anti-arthritic effect and explore the potential mechanism of action on collagen-induced arthritis (CIA) in rats. CIA was induced by immunizing 50 female Wistar rats with bovine type II collagen. 13 days following the immunization rats with CIA were treated with SSBH (50mg/kg), leflunomide (LEF) (10mg/kg) and physiological saline for 30 days, and rats without CIA were left untreated. After the treatment, paw edema was obviously improved in SSBH-treated rats, with the significant difference of arthritis score (F=6.032, P=0.006) observed between the three treated groups. In pathological observation, SSBH-treated rats showed a significant improvement of inflammatory infiltration, synovial hyperplasia, cartilage and bone destruction and joint fusion. After the treatment of SSBH, radiological score of knee (t=11.504, P=0.000) and ankle joints (t=9.250, P=0.000) was decreased significantly. In situ hybridization on joint tissue section indicated only slight synovial hyperblastosis and expression of NF-kappaB in SSBH-treated rats. Image analysis indicated a significant difference of means of integrated optical density (MIOD) (F=3.956, P=0.040) and means of stained area (MSA) (F=3.867, P=0.032) of NF-kappaB between the three treated groups. MIOD and MSA of SSBH-treated group were significantly lower vs control. Enzyme linked immunosorbent assay (ELISA) showed a significant difference (F=10.167, P=0.000) of the amount of p-p38 MAPKalpha in the three treated groups. The detected amount of p-p38 MAPKalpha in SSBH-treated group was significantly lower vs control. These results show SSBH has an inhibiting effect on CIA, which may be associated with NF-kappaB and p38 MAPKalpha.

Linkage and association studies of joint morbidity from rheumatoid arthritis

OBJECTIVE

To investigate the relationship between genetic variations of rheumatoid arthritis (RA) susceptibility in terms of joint morbidity.

METHODS

We used data from Genetic Analysis Workshop 15. The Illumina linkage panel IV included 5858 single-nucleotide polymorphisms (SNP), with 5744 SNP passing quality control filters. The phenotypic variables analyzed were the level of rheumatoid factor (RF) and score on the Joint Alignment and Motion (JAM) scale. We modified the scale, dividing by RF values relevant to disease severity. Linkage analysis for affected sibling pairs was done using the MERLIN program, and family-based association tests were carried out using PLINK and FBAT software.

RESULTS

We found a high peak (LOD = 3.29; NPL Z = 4.07) near the HLA-DRB1 region on chromosome 6. The linkage at 6p24 at rs1410766 [LOD = 2.66; nonparametric linkage (NPL) Z = 3.23] was statistically significant. Two other regions also showed possible linkage peaks: chromosome 7q30 at rs322812 (LOD = 2.47; NPL Z = 3.39) and chromosome 15p34 at rs347117 (LOD = 1.95; NPL Z = 2.80). For the family-based association study, 7 SNP related to clinical RA severity were detected.

CONCLUSION

Genetic variations may lead to an enhanced risk of joint damage and increased levels of RF. Further studies are needed to elucidate the roles of other genes involved in RA and to explore whether the clinical signs of RA are associated with particular genetic variations.

Use of supplementary phenotype to identify additional rheumatoid arthritis loci in a linkage analysis of 342 UK affected sibling pair families

Background

Although rheumatoid arthritis has been shown to have moderately strong genetic component, both linked loci identified in linkage analyses and susceptibility variants from association studies are short of adequately accounting for a comprehensive catalogue of the molecular factors underlying this complex disease. The objective of this study was to use supplementary phenotype based on cumulative hazard of rheumatoid arthritis to identify linkage evidence for new and additional rheumatoid arthritis loci in a genome-wide linkage analysis of 342 affected sibling pair families from the United Kingdom.

Methods

Using proportional hazards model, we estimated cumulative hazard of rheumatoid arthritis and then used it as a quantitative trait in a non-parametric multipoint variance component linkage analysis with 353 microsatellite markers distributed across the 22 autosomal chromosomes.

Results

We identified 3 new loci with genome-wide suggestive linkage evidence for rheumatoid arthritis on 9q21.13, 15p11.1 and 20q13.33. Our results also confirmed previously reported linkage evidence in the HLA-DRB1 region on chromosome 6 and on locus 1q32.1.

Conclusion

This study demonstrates the potential for information gain through the use of supplementary phenotypes in genetic study of complex diseases to identify new and additional potential linked loci that are not detected by linkage analysis of traditional phenotypes; and our results provide further evidence of the involvement of multiple loci in the genetic aetiology of rheumatoid arthritis.

Haplotype association analysis of North American Rheumatoid Arthritis Consortium data using a generalized linear model with regularization

The Genetic Analysis Workshop 16 rheumatoid arthritis data include a set of 868 cases and 1194 controls genotyped at 545,080 single-nucleotide polymorphisms (SNPs) from the Illumina 550 k chip. We focus on investigating chromosomes 6 and 18, which have 35,574 and 16,450 SNPs, respectively. Association studies, including single SNP and haplotype-based analyses, were applied to the data on those two chromosomes. Specifically, we conducted a generalized linear model with regularization (rGLM) approach for detecting disease-haplotype association using unphased SNP data. A total of 444 and 43 four-SNP tests were found to be significant at the Bonferroni corrected 5% significance level on chromosome 6 and 18, respectively.

Comparison between the stochastic search variable selection and the least absolute shrinkage and selection operator for genome-wide association studies of rheumatoid arthritis

Background

Because multiple loci control complex diseases, there is great interest in testing markers simultaneously instead of one by one. In this paper, we applied two model selection algorithms: the stochastic search variable selection (SSVS) and the least absolute shrinkage and selection operator (LASSO) to two quantitative phenotypes related to rheumatoid arthritis (RA).

Results

The Genetic Analysis Workshop 16 data includes 2,062 unrelated individuals and 545,080 single-nucleotide polymorphism markers from the Illumina 550 k chip. We performed our analyses on the cases as the quantitative phenotype data was not provided for the controls. The performance of the two algorithms was compared. Using sure independence screening as the prescreening procedure, both SSVS and LASSO give small models. No markers are identified in the human leukocyte antigen region of chromosome 6 that was shown to be associated with RA. SSVS and LASSO identify seven common loci, and some of them are on genes LRRC8D, LRP1B, and COLEC12. These genes have not been reported to be associated with RA. LASSO also identified a common locus on gene KTCD21 for the two phenotypes (marker rs230662 and rs483731, respectively).

Conclusion

SSVS outperforms LASSO in simulation studies. Both SSVS and LASSO give small models on the RA data, however this depends on model parameters. We also demonstrate the ability of both LASSO and SSVS to handle more markers than the number of samples.

The ITGAV rs3738919 variant and susceptibility to rheumatoid arthritis in four Caucasian sample sets

INTRODUCTION

Angiogenesis is an important process in the development of destructive synovial pannus in rheumatoid arthritis (RA). The ITGAV +gene encodes a cell cycle-associated antigen, integrin alphanubeta 3, which plays a role in RA angiogenesis. Previously, two independent studies identified an association between the major allele of the ITGAV single-nucleotide polymorphism (SNP) rs3738919 and RA. We therefore tested this association in an independent study using New Zealand (NZ) and Oxford (UK) RA case control samples.

METHODS

We compared genotype frequencies in 740 NZ Caucasian RA patients and 553 controls genotyped for rs3738919, using a polymerase chain reaction-restriction fragment length polymorphism assay. A TaqMan genotyping SNP assay was used to type 713 Caucasian RA patients and 515 control samples from Oxford for the rs3738919 variant. Association of rs3738919 with RA was tested in these two sample sets using the chi-square goodness-of-fit test. The Mantel-Haenszel test was used to perform a meta-analysis, combining the genetic results from four independent Caucasian case control cohorts, consisting of 3,527 cases and 4,126 controls. Haplotype analysis was also performed using SNPs rs3911238, rs10174098 and rs3738919 in the Wellcome Trust Case Control Consortium, NZ and Oxford case control samples.

RESULTS

We found no evidence for association between ITGAV and RA in either the NZ or Oxford sample set (odds ratio [OR] = 0.88, P(allelic) = 0.11 and OR = 1.18, P(allelic) = 0.07, respectively). Inclusion of these data in a meta-analysis (random effects) of four independent cohorts (3,527 cases and 4,126 controls) weakens support for the hypothesis that rs3738919 plays a role in the development of RA (OR(combined) = 0.92, 95% confidence interval 0.80 to 1.07; P = 0.29). No consistent haplotype associations were evident.

CONCLUSIONS

Association of ITGAV SNP rs7378919 with RA was not replicated in NZ or Oxford case control sample sets. Meta-analysis of these and previously published data lends limited support for a role for the ITGAV in RA in Caucasians of European ancestry.

Association of the X-chromosomal genes TIMP1 and IL9R with rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is an inflammatory joint disease with features of an autoimmune disease with female predominance. Candidate genes located on the X-chromosome were selected for a family trio-based association study.

METHODS

A total of 1452 individuals belonging to 3 different sample sets were genotyped for 16 single-nucleotide polymorphisms (SNP) in 7 genes. The first 2 sets consisted of 100 family trios, each of French Caucasian origin, and the third of 284 additional family trios of European Caucasian origin. Subgroups were analyzed according to sex of patient and presence of anti-cyclic citrullinated peptide (anti-CCP) autoantibodies.

RESULTS

Four SNP were associated with RA in the first sample set and were genotyped in the second set. In combined analysis of sets 1 and 2, evidence remained for association of 3 SNP in the genes UBA1, TIMP1, and IL9R. These were again genotyped in the third sample set. Two SNP were associated with RA in the joint analysis of all samples: rs6520278 (TIMP1) was associated with RA in general (p = 0.035) and rs3093457 (IL9R) with anti-CCP-positive RA patients (p = 0.037) and male RA patients (p = 0.010). A comparison of the results with data from whole-genome association studies further supports an association of RA with TIMPL The sex-specific association of rs3093457 (IL9R) was supported by the observation that men homozygous for rs3093457-CC are at a significantly higher risk to develop RA than women (risk ratio male/female = 2.98; p = 0.048).

CONCLUSION

We provide evidence for an association of at least 2 X-chromosomal genes with RA: TIMP1 (rs6520278) and IL9R (rs3093457).

Meta-analysis of genome-wide linkage studies across autoimmune diseases

Autoimmune diseases are chronic disorders initiated by a loss of immunologic tolerance to self-antigens. They cluster within families, and patients may be diagnosed with more than one disease, suggesting pleiotropic genes are involved in the aetiology of different diseases. To identify potential loci, which confer susceptibility to autoimmunity independent of disease phenotype, we pooled results from genome-wide linkage studies, using the genome scan meta-analysis method (GSMA). The meta-analysis included 42 independent studies for 11 autoimmune diseases, using 7350 families with 18 291 affected individuals. In addition to the HLA region, which showed highly significant genome-wide evidence for linkage, we obtained suggestive evidence for linkage on chromosome 16, with peak evidence at 10.0-19.8 Mb. This region may harbour a pleiotropic gene (or genes) conferring risk for several diseases, although no such gene has been identified through association studies. We did not identify evidence for linkage at several genes known to confer increased risk to different autoimmune diseases (PTPN22, CTLA4), even in subgroups of diseases consistently found to be associated with these genes. The relative risks conferred by variants in these genes are modest (<1.5 in most cases), and even a large study like this meta-analysis lacks power to detect linkage. This study illustrates the concept that linkage and association studies have power to identify very different types of disease-predisposing variants.

Two loci on chromosome 15 control experimentally induced arthritis through the differential regulation of IL-6 and lymphocyte proliferation

Using genetic linkage analysis of proteoglycan-induced arthritis (PGIA), a murine model for rheumatoid arthritis, we identified two loci, Pgia8 and Pgia9, on chromosome 15 (chr15) that appear to be implicated in disease susceptibility. Immunization of congenic strains carrying the entire chr15 and separately each of the two loci of DBA/2 arthritis-resistant origin in susceptible BALB/c background confirmed locations of two loci on chr15: the major Pgia9 and lesser Pgia8 locus. Distal part of chr15 (Pgia9) showed a major suppressive effect on PGIA susceptibility in females (40%, p < 0.001), whereas the effect of this locus in congenic males was still significant but weaker. Proximal part of chr15 (Pgia8) demonstrated mild and transient effect upon arthritis; this effect was PGIA-promoting in males and suppressive in females. Pgia8 and Pgia9 loci demonstrated an additive mode of inheritance, since when they were both incorporated in consomic chr15 strain, the total effect was a sum of the two loci. Using F(2) population of the intercross of wild-type and chr15 consomic strain, we confirmed and refined quantitative trait locus positions and identified a strong correlation between disease susceptibility and lymphocyte-producing cytokines of TNF-alpha and IL-6. Both Pgia8 and Pgia9 loci on chr15 appear to control IL-6 production in spleen cultures of arthritic mice, providing an important link to the mechanism of autoimmune inflammation.

Congenic strains displaying similar clinical phenotype of arthritis represent different immunologic models of inflammation

Proteoglycan (PG)-induced arthritis (PGIA) is an autoimmune inflammatory disease controlled by multiple genes in the murine genome. BALB/c x DBA/2 congenic strains carrying four major PGIA chromosome loci were immunized, and positions of loci on chromosomes 3, 7, 8 and 19 (loci Pgia26, Pgia21, Pgia4 and Pgia12, respectively) were confirmed. Each congenic strain exhibited a different pattern of regulation of clinical and immunologic features of PGIA, and these features were significantly influenced by gender. Locus Pgia26 delayed PGIA onset in males and females, and the effect was associated with a lower rate of antigen-induced lymphocyte proliferation and lower production of interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and interleukin-4 (IL-4). Pgia12 similarly delayed onset in males, but the effect was achieved by elevated proliferation of PG-specific lymphocytes and enhanced production of IFN-gamma and IL-4. The effect of the Pgia21 locus was arthritis-suppressive in females but PGIA-permissive in congenic males. These opposite effects are attributed to two-fold higher serum autoantibody and IL-6 levels in males than in females. Our study supports the idea that each congenic strain represents a different immunologic subtype of PGIA, providing an explanation for the complex etiology and various clinical phenotypes of rheumatoid arthritis.

Linkage analysis of anti-CCP levels as dichotomized and quantitative traits using GAW15 single-nucleotide polymorphism scan of NARAC families

Rheumatoid arthritis is a clinically and genetically heterogeneous disease. Anti-cyclic citrullinated (anti-CCP) antibodies have a high specificity for rheumatoid arthritis and levels correlate with disease severity. The focus of this study was to examine whether analyzing anti-CCP levels could increase the power of linkage analysis by identifying a more homogeneous subset of rheumatoid arthritis patients. We also wanted to compare linkage signals when analyzing anti-CCP levels as dichotomized (CCP_binary), categorical (CCP_cat), and continuous traits, with and without transformation (log_CCP and CCP_cont). Illumina single-nucleotide polymorphism scans of the North American Rheumatoid Arthritis Consortium families were analyzed for four chromosomes (6, 7, 11, 22) using nonparametric linkage (NPL) (rheumatoid arthritis and CCP_binary), regress (CCP_cat and Log_CCP), and deviates (CCP_cont) analysis options as implemented in Merlin. Similar linkage results were obtained from analyses of rheumatoid arthritis, CCP_binary, and CCP_cont. The only exception was that we observed improved linkage signals and a narrower region for CCP_binary as compared to a clinical diagnosis of rheumatoid arthritis alone on chromosome 7, a region which previously showed variation in linkage results with rheumatoid arthritis according to anti-CCP levels. Analyses of CCP_cat and Log_CCP had little power to detect linkage. Our data suggested that linkage analyses of anti-CCP levels may facilitate identification of rheumatoid arthritis genes but quantitative analyses did not further improve power. Our study also highlighted that quantitative trait linkage results are highly sensitive to phenotype transformation and analytic approaches.

Multilocus analysis of GAW15 NARAC chromosome 18 case-control data

The Genetic Analysis Workshop 15 rheumatoid arthritis data included a set of 460 cases and 460 controls genotyped at 2300 closely spaced markers on a 10 megabase region of chromosome 18q. We conducted a multilocus analysis of these data using a localized haplotype clustering method that adapts to linkage disequilibrium structure and can be applied to large, densely genotyped data sets such as this one. We found a protective haplotype carried by 33 individuals that was significantly associated with rheumatoid arthritis in these data after adjusting for multiple testing. This haplotype was located less than 500 base pairs upstream of the CCBE1 gene. The association was not detected using single-marker tests, but could be found using a variety of multilocus tests.

One- and two-locus models for mapping rheumatoid arthritis-susceptibility genes on chromosome 6

To evaluate whether there is evidence for two rheumatoid arthritis (RA) susceptibility genes on chromosome 6, we applied new robust methods for two-locus multipoint identical-by-descent mapping to the rheumatoid arthritis data of the Genetic Analysis Workshop 15. The software GEEARP was used to estimate the locations and the corresponding genetic effects for one locus or two linked loci in a region on chromosome 6, on the basis of affected relative pairs. These methods were applied to the data sets from the North American Rheumatoid Arthritis Consortium, Canada, France, and the first screen of United Kingdom. From the resultant 95% confidence intervals given by a robust variance estimator, a linked region, other than the well-known HLA region, was at 54.7–69.6 cM, providing evidence for a second rheumatoid arthritis susceptibility locus on chromosome 6.

Association of ITGAV supports a role of angiogenesis in rheumatoid arthritis

Motivated by linkage data and the hypothesis that angiogenesis plays a functional role in rheumatoid arthritis (RA), Jacq and colleagues present a family-based, multi-stage, candidate gene association study in French and European Caucasians in a paper on the association of the ITGAV rs3738919-C variant allele with RA (C-containing genotypes: odds ratio 1.94, confidence interval 1.3 to 2.9, P = 0.002). Support comes from a recent genome-wide study, which on its own would have missed identifying the association. Further research into the associating variant will require detailed haplotype analysis, verification in further studies, and research involving intermediate phenotypes or direct functional experiments. This new RA risk factor supports the role of angiogenesis in the disease.

The ITGAV rs3738919-C allele is associated with rheumatoid arthritis in the European Caucasian population: a family-based study

The integrin αvβ3, whose αv subunit is encoded by the ITGAV gene, plays a key role in angiogenesis. Hyperangiogenesis is involved in rheumatoid arthritis (RA) and the ITGAV gene is located in 2q31, one of the suggested RA susceptibility loci. Our aim was to test the ITGAV gene for association and linkage to RA in a family-based study from the European Caucasian population.

Two single nucleotide polymorphisms were genotyped by PCR-restriction fragment length polymorphism in 100 French Caucasian RA trio families (one RA patient and both parents), 100 other French families and 265 European families available for replication. The genetic analyses for association and linkage were performed using the comparison of allelic frequencies (affected family-based controls), the transmission disequilibrium test, and the genotype relative risk.

We observed a significant RA association for the C allele of rs3738919 in the first sample (affected family-based controls, RA index cases 66.5% versus controls 56.7%; P = 0.04). The second sample showed the same trend, and the third sample again showed a significant RA association. When all sets were combined, the association was confirmed (affected family-based controls, RA index cases 64.6% versus controls 58.1%; P = 0.005). The rs3738919-C allele was also linked to RA (transmission disequilibrium test, 56.5% versus50% of transmission; P = 0.009) and the C-allele-containing genotype was more frequent in RA index cases than in controls (RA index cases 372 versus controls 339; P = 0.002, odds ratio = 1.94, 95% confidence interval = 1.3–2.9).

The rs3738919-C allele of the ITGAV gene is associated with RA in the European Caucasian population, suggesting ITGAV as a new minor RA susceptibility gene.

Neo-ligands for innate immune receptors and the etiology of sterile inflammatory disease

Microbe recognition based on a small collection of germline-encoded receptors carries a hidden liability: the possibility that mutational changes in the proteome will lead to self-recognition. The risk of self-recognition is enhanced, because innate immune receptors display low specificity, as they are driven to accommodate heterogeneous signature molecules found in the microbial world. The proteome structure is globally constrained by the innate immune sensing apparatus to satisfy a proscription against self-reactivity. But accidents happen, and here it is proposed that mutations creating neo-ligands for innate immune receptors are the proximal cause of sterile inflammatory diseases, which in turn embody the selective pressure that constrains the proteome. Such mutations are predictably dominant and may occur in the germline and also in somatic cells (e.g. in lymphocytes), causing inflammatory effects upon clonal expansion. They may also account for the inflammatory character of selected neoplastic diseases. The neo-ligand hypothesis accounts for the heritability, ambiguous linkage characteristics, phenotypic heterogeneity, and natural history of diverse forms of sterile inflammation. It explains sterile inflammatory diseases as conditions in which aberrant immune signaling is caused by proteome encroachment upon the ligand-recognition space over which the innate immune system stands guard.

Data for Genetic Analysis Workshop (GAW) 15 Problem 2, genetic causes of rheumatoid arthritis and associated traits

For Genetic Analysis Workshop 15 Problem 2, we organized data from several ongoing studies designed to identify genetic and environmental risk factors for rheumatoid arthritis. Data were derived from the North American Rheumatoid Arthritis Consortium (NARAC), collaboration among Canadian researchers, the European Consortium on Rheumatoid Arthritis Families (ECRAF), and investigators from Manchester, England. All groups used a common standard for defining rheumatoid arthritis, but NARAC also further selected for a more severe phenotype in the probands. Genotyping and family structures for microsatellite-based linkage analysis were provided from all centers. In addition, all centers but ECRAF have genotyped families for linkage analysis using SNPs and these data were additionally provided. NARAC also had additional data from a dense genotyping analysis of a region of chromosome 18 and results from candidate gene studies, which were provided. Finally, smoking influences risk for rheumatoid arthritis, and data were provided from the NARAC study on this behavior as well as some additional phenotypes measuring severity. Several questions could be evaluated using the data that were provided. These include comparing linkage analysis using single-nucleotide polymorphisms versus microsatellites and identifying credible regions of linkage outside the HLA region on chromosome 6p13, which has been extensively documented; evaluating the joint effects of smoking with genetic factors; and identifying more homogenous subsets of families for whom genetic susceptibility might be stronger, so that linkage and association studies may be more efficiently conducted.

Identifying single-nucleotide polymorphisms responsible for the linkage signal of rheumatoid arthritis on chromosome 6 by joint modeling of linkage and association

This study evaluated the utility of unrelated controls and flanking markers when performing joint modeling of linkage and association by the LAMP software (version 0.0.6) [Am J Hum Genet 2005, 76:934–949; Am J Hum Genet 2006, 78:778–792]. Analyses were conducted on the simulated rheumatoid arthritis (RA) data in Genetic Analysis Workshop 15 (GAW15), using single-nucleotide polymorphisms (SNPs) on chromosome 6 over the 100 simulated replicates. We found that the LOD score for testing association in the presence of linkage dramatically increased when unrelated controls were added to affected sib pairs (ASPs), and that choosing a sufficient number of flanking markers is critical in order to distinguish between perfect linkage disequilibrium (which leads to the conclusion of a measured SNP explaining a linkage signal) and incomplete linkage disequilibrium (which leads to the conclusion of other undetected causal variants in a linkage region).

Constructing gene association networks for rheumatoid arthritis using the backward genotype-trait association (BGTA) algorithm

BACKGROUND

Rheumatoid arthritis (RA, MIM 180300) is a common and complex inflammatory disorder. The North American Rheumatoid Arthritis Consortium (NARAC) data, as part of the Genetic Analysis Workshop 15 data, consists of both genome scan and candidate gene studies on RA patients.

RESULTS

We applied the backward genotype-trait association (BGTA) algorithm to capture marginal and gene x gene interaction effects of multiple susceptibility loci on RA disease status. A two-stage screening approach was used for the genome scan, whereas a comprehensive study of all possible subsets was conducted for the candidate genes. For the genome scan, we constructed an association network among 39 genetic loci that demonstrated strong signals, 19 of which have been reported in the RA literature. For the candidate genes, we found strong signals for PTPN22 and SUMO4. Based on significant association evidence, we built an association network among the loci of PTPN22, PADI4, DLG5, SLC22A4, SUMO4, and CARD15. To control for false positives, we used permutation tests to constrain the family-wise type I error rate to 1%.

CONCLUSION

Using the BGTA algorithm, we identified genetic loci and candidate genes that were associated with RA susceptibility and association networks among them. For the first time, we report possible interactions between single-nucleotide polymorphisms/genes, which may be useful for biological interpretation.

Large-scale linkage analysis of 1302 affected relative pairs with rheumatoid arthritis

Rheumatoid arthritis is the most common systematic autoimmune disease and its etiology is believed to have both strong genetic and environmental components. We demonstrate the utility of including genetic and clinical phenotypes as covariates within a linkage analysis framework to search for rheumatoid arthritis susceptibility loci. The raw genotypes of 1302 affected relative pairs were combined from four large family-based samples (North American Rheumatoid Arthritis Consortium, United Kingdom, European Consortium on Rheumatoid Arthritis Families, and Canada). The familiality of the clinical phenotypes was assessed. The affected relative pairs were subjected to autosomal multipoint affected relative-pair linkage analysis. Covariates were included in the linkage analysis to take account of heterogeneity within the sample. Evidence of familiality was observed with age at onset (p << 0.001) and rheumatoid factor (RF) IgM (p << 0.001), but not definite erosions (p = 0.21). Genome-wide significant evidence for linkage was observed on chromosome 6. Genome-wide suggestive evidence for linkage was observed on chromosomes 13 and 20 when conditioning on age at onset, chromosome 15 conditional on gender, and chromosome 19 conditional on RF IgM after allowing for multiple testing of covariates.

HSPD1 is not a major susceptibility gene for rheumatoid arthritis in the French Caucasian population

The heat shock 60-kDa protein 1 (HSP60) is involved in immune and inflammatory reactions, which are hallmarks of rheumatoid arthritis (RA). HSP60 is encoded by the HSPD1 gene located on 2q33, one of the suggested RA susceptibility loci in the French Caucasian population. Our aim was to test whether HSPD1 is a major susceptibility gene by studing families from the French Caucasian population. Three single nucleotide polymorphisms (SNPs) were studied in 100 RA trio families, and 100 other families were used for replication. Genetic analyses were performed by comparing allelic frequencies, by applying the transmission disequilibrium test, and by assessing the genotype relative risk. We observed a significant RA association for the C/C genotype of rs2340690 in the first sample. However, this association was not confirmed when the second sample was added. The two other SNPs and the haplotype analysis did not give any significant results. We conclude that HSPD1 is not a major RA susceptibility gene in the French Caucasian population.

Association of arthritis with a gene complex encoding C-type lectin-like receptors

OBJECTIVE

To identify susceptibility genes in a rat model of rheumatoid arthritis (RA) and to determine whether the corresponding human genes are associated with RA.

METHODS

Genes influencing oil-induced arthritis (OIA) were position mapped by comparing the susceptibility of inbred DA rats with that of DA rats carrying alleles derived from the arthritis-resistant PVG strain in chromosomal fragments overlapping the quantitative trait locus Oia2. Sequencing of gene complementary DNA (cDNA) and analysis of gene messenger RNA (mRNA) expression were performed to attempt to clone a causal gene. Associations with human RA were evaluated by genotyping single-nucleotide polymorphisms (SNPs) in the corresponding human genes and by analyzing frequencies of alleles and haplotypes in RA patients and age-, sex-, and area-matched healthy control subjects.

RESULTS

Congenic DA rats were resistant to OIA when they carried PVG alleles for the antigen-presenting lectin-like receptor gene complex (APLEC), which encodes immunoregulatory C-type lectin-like receptors. Multiple differences in cDNA sequence and mRNA expression precluded cloning of a single causal gene. Five corresponding human APLEC genes were identified and targeted. The SNP rs1133104 in the dendritic cell immunoreceptor gene (DCIR), and a haplotype including that marker and 4 other SNPs in DCIR and its vicinity showed an indication of allelic association with susceptibility to RA in patients who were negative for antibodies to cyclic citrullinated peptide (anti-CCP), with respective odds ratios of 1.27 (95% confidence interval [95% CI] 1.06-1.52; uncorrected P = 0.0073) and 1.37 (95% CI 1.12-1.67; uncorrected P = 0.0019). Results of permutation testing supported this association of the haplotype with RA.

CONCLUSION

Rat APLEC is associated with susceptibility to polyarthritis, and human APLEC and DCIR may be associated with susceptibility to anti-CCP-negative RA.

Contribution of genetic studies in rodent models of autoimmune arthritis to understanding and treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic and potentially debilitating autoimmune disease. While novel therapies have emerged in recent years, disease remission is rarely achieved. RA is a complex trait, and the identifying of its susceptibility and severity genes has been anticipated to generate new targets for therapeutic intervention. However, finding those genes and understanding their function has been a challenging task. Studies in rodent intercrosses and congenics generated from inbred strains have been an important complementary strategy to identify arthritis genes, and understand how they operate to regulate disease. Furthermore, these new rodent arthritis genes will be new targets for therapeutic interventions, and will identify new candidate genes or candidate pathways for association studies in RA. In this review-opinion article I discuss RA genetics, difficulties involved in gene identification, and how rodent models can facilitate (1) the discovery of both arthritis susceptibility and severity genes, (2) studies of gene-environment interactions, (3) studies of gene-gender interactions, (4) epistasis, (5) functional characterization of the specific genes, (6) development of novel therapies and (7) how the information generated from rodent studies will be useful to understanding and potentially treating RA.

Meta-analysis of HLA-DRB1 polymorphism in Latin American patients with rheumatoid arthritis

OBJECTIVES

To estimate the common effect size of HLA-DRB1 alleles on rheumatoid arthritis (RA) susceptibility across Latin America populations through a meta-analysis combining the results of published data.

METHODS

Case-control studies on HLA-DRB1 association with RA in Latin America were searched up to October 2006. Genotype frequencies were extracted according to both shared epitope (SE) and HLA-DR4 positive or negative alleles. The effect summary odds ratio (OR) and 95% confidence intervals was obtained. Heterogeneity and publication bias were assessed.

RESULTS

Eight studies containing 684 cases and 1015 controls were included. Under the random effects model, the common OR was 3.28 (1.93, 5.60) (p<0.0001) and 3.54 (2.47, 5.05) (p=4.22 x 10(-12)) for HLA-DR4 and SE, respectively. There was no evidence of publication bias according to Funnel plot and Egger's regression test (p=0,445 for DR4 and p=0,464 for SE meta-analysis). Significant heterogeneity was observed for HLA-DR4 (I2=81.06%, Q=36.96, p=0.000005) but not for the SE meta-analysis.

CONCLUSIONS

HLA-DR4 and SE positive HLA-DRB1 alleles (mainly HLA-DRB10404) are associated with RA in Latin Americans. Heterogeneity is expected owing to the diverse degree of admixture between the examined populations. Our findings support the HLA as a major susceptibility locus for RA and validate the SE hypothesis in Latin America.

The association of HLA-DRB1 alleles with rheumatoid arthritis in the Chinese Shantou population: a follow-up study

We investigated the distribution of HLA-DRB1 alleles in a sample of the Chinese Shantou population, and explored the relationship between HLA-DRB1 alleles and the susceptibility and clinical features of rheumatoid arthritis (RA). We studied 117 consecutive patients with RA and control groups, including 38 cases of systemic lupus erythematosus and 100 healthy individuals. HLA-DRB1 genotyping was performed using PCR with sequence-specific primers. HLA-DRB1*04 subtypes were detected using spot hybridization of PCR products with sequence-specific oligonucleotide probes. We compared the frequency of HLA-DRB1 alleles in healthy control patients with that in patients with RA. Patients with RA were evaluated for sex, age at disease onset, disease duration, extra-articular involvement, presence of autoantibodies, global functional status, and radiographic damage. The frequency of HLA-DRB1*04 was found to be significantly higher in RA patients than in healthy individuals (49.6% vs 18.0%, odds ratio = 4.478, P < 0.001). HLA-DRB1*0405 was the most prominently associated subtype in RA patients (62.1% vs 27.8%, odds ratio = 4.255, P = 0.011). Compared with the HLA-DRB1*04-negative RA group, the mean duration of RA in the HLA-DRB1*04-positive RA group was longer, and the mean age at disease onset was lower. A 2-9 year follow-up study was performed, and the risk factors associated with the radiographic progression of RA were determined. Logistic regression analysis revealed that only HLA-DRB1*04 alleles were significantly associated with the radiographic progression of RA (B = 2.652, P = 0.018, Exp(B) = 14.182). Our observations indicated that the HLA-DRB1*04 alleles, especially the subtype HLA-DRB1*0405, were significantly associated with RA susceptibility in the Chinese Shantou population. The HLA-DRB1*04 alleles may be associated with the severity of RA.

Cia25 on rat chromosome 12 regulates severity of autoimmune arthritis induced with pristane and with collagen

BACKGROUND

A genomewide scan in a DA x ACI F2 intercross studied for collagen-induced arthritis (CIA) identified the severity quantitative trait locus Cia25 on rat chromosome 12. Cia25 co-localises with loci regulating several forms of autoimmune diseases in rats, mice and humans, suggesting a common gene.

OBJECTIVE

To characterise the effects of Cia25 on severity of arthritis in congenic rats.

METHODS

DA.ACI(Cia25) congenic rats were constructed according to a genotype-guided strategy, and tested for pristane-induced arthritis (PIA) and CIA, induced with rat type II collagen (CII). A well-established scoring system previously shown to correlate with histological damage, including cartilage and bone erosions, synovial hyperplasia and synovial inflammation, was used.

RESULTS

The introgression of ACI alleles at Cia25 into DA background, as in DA.ACI(Cia25) rats, was enough to significantly reduce arthritis severity by 60% in PIA and by 40% in CIA, both in males and females compared with DA rats of the same sex. Levels of IgG anti-CII in male DA.ACI(Cia25) rats were 83% lower than in male DA. Levels of anti-CII in females were not affected by the congenic interval.

CONCLUSIONS

Cia25 contains a gene that regulates disease severity in two distinct models of autoimmune arthritis. Although both genders were protected in arthritis studies, only male congenic rats had a dramatic reduction in levels of anti-CII, suggesting the possibility of a second arthritis gene in this interval that operates via the regulation of autoantibodies in a sex-specific manner. The identification of the gene(s) accounting for Cia25 is expected to generate novel prognostic biomarkers and targets for therapy.

Genetic association between the PRKCH gene encoding protein kinase Ceta isozyme and rheumatoid arthritis in the Japanese population

OBJECTIVE

Analyses of families with rheumatoid arthritis (RA) have suggested the presence of a putative susceptibility locus on chromosome 14q21-23. This large population-based genetic association study was undertaken to examine this region.

METHODS

A 2-stage case-control association study of 950 unrelated Japanese patients with RA and 950 healthy controls was performed using >400 gene-based common single-nucleotide polymorphisms (SNPs).

RESULTS

Multiple SNPs in the PRKCH gene encoding the eta isozyme of protein kinase C (PKCeta) showed significant single-locus disease associations, the most significant being SNP c.427+8134C>T (odds ratio 0.72, 95% confidence interval 0.62-0.83, P = 5.9 x 10(-5)). Each RA-associated SNP was consistently mapped to 3 distinct regions of strong linkage disequilibrium (i.e., linkage disequilibrium or haplotype blocks) in the PRKCH gene locus, suggesting that multiple causal variants influence disease susceptibility. Significant SNPs included a novel common missense polymorphism of the PRKCH gene, V374I (rs2230500), which lies within the ATP-binding site that is highly conserved among PKC superfamily members. In circulating lymphocytes, PRKCH messenger RNA was expressed at higher levels in resting T cells (CD4(+) or CD8(+)) than in B cells (CD19(+)) or monocytes (CD14(+)) and was significantly down-regulated through immune responses.

CONCLUSION

Our results provide evidence of the involvement of PRKCH as a susceptibility gene for RA in the Japanese population. Dysregulation of PKCeta signal transduction pathway(s) may confer increased risk of RA through aberrant T cell-mediated autoimmune responses.

Linkage proof for PTPN22, a rheumatoid arthritis susceptibility gene and a human autoimmunity gene

The tyrosine phosphatase PTPN22 allele 1858T has been associated with rheumatoid arthritis (RA) and other autoimmune diseases. RA is the most frequent of those multifactorial diseases. The RA association was usually restricted to serum rheumatoid factor positive disease (RF+). No interaction was shown with HLA-DRB1, the first RA gene. Many case-control studies replicated the RA association, showing an allele frequency increase of approximately 5% on average and large variations of population allele frequencies (2.1-15.5%). In multifactorial diseases, the final proof for a new susceptibility allele is provided by departure from Mendel's law (50% transmission from heterozygous parents). For PTPN22-1858T allele, convincing linkage proof was available only for type 1 diabetes. We aimed at providing this proof for RA. We analyzed 1,395 West European Caucasian individuals from 465 "trio" families. We replicated evidence for linkage, demonstrating departure from Mendel's law in this subset of early RA onset patients. We estimated the overtransmission of the 1858T allele in RF+ families: T = 63%, P < 0.0007. The 1858T allele frequency increased from 11.0% in controls to 17.4% in RF+ RA for the French Caucasian population and the susceptibility genotype (1858T/T or T/C) from 20.2% to 31.6% [odds ratio (OR) = 1.8 (1.2-2.8)]. In conclusion, we provided the linkage proof for the PTPN22-1858T allele and RF+ RA. With diabetes and RA, PTPN22 is therefore a "linkage-proven" autoimmunity gene. PTPN22 accounting for approximately 1% of the RA familial aggregation, many new genes could be expected that are as many leads to definitive therapy for autoimmune diseases.

The TNFRSF1A R92Q mutation is frequent in rheumatoid arthritis but shows no evidence for association or linkage with the disease

OBJECTIVE

TNFRSF1A mutations cause TNFRSF1A-associated periodic syndrome (MIM#142680). A recent study suggested that the R92Q mutation was associated with polyarthritis. We aimed to search for this and other TNFRSF1A mutations in rheumatoid arthritis (RA), and to test for linkage.

METHODS

The DNA of 100 trio families and 86 index cases of RA-affected sib-pair (ASP) families from the French Caucasian population were investigated by denatured high-performance liquid chromatography for TNFRSF1A mutations in exons 2 to 4. The test for association compared cases and controls (derived from un-transmitted parental chromosomes). The test for linkage relied on the transmission disequilibrium test (TDT) in trio families and cosegregation in ASP families.

RESULTS

Only the R92Q mutation was detected--in 2 of the 100 index cases of trio families and in 5 (5.8%) of the index cases of ASP families, but also in 5% of the controls, showing no association with the disease. No RA linkage evidence was found in TDT and ASP RA families.

CONCLUSION

This TNFRSF1A investigation in RA from the French Caucasian population showed only the R92Q mutation, with a frequency of 4.5%, but no evidence for RA association or linkage to the disease. The R92Q mutation could be considered to be a low-penetrance variant.