Margreet Kloppenburg

Smoking is a risk factor for anti-CCP antibodies only in rheumatoid arthritis patients who carry HLA-DRB1 shared epitope alleles

Objectives: To study the gene–environment interaction of tobacco exposure and shared epitope on autoantibodies in patients with rheumatoid arthritis and undifferentiated arthritis. Methods: From incident cases of arthritis (n = 1305), patients who did not fulfil any classification criteria (undifferentiated arthritis (n = 486)) and those who fulfilled the American College of Rheumatology criteria for rheumatoid arthritis (n = 407) were identified. IgM rheumatoid factor (RF), anti-cyclic-citrullinated peptide (CCP) antibodies, and HLA-DRB1 alleles were determined. Results: In rheumatoid arthritis, an interaction was found between tobacco exposure and shared epitope for the presence of anti-CCP antibodies, as the odds ratio for anti-CCP antibodies in patients having both tobacco exposure (TE) and shared epitope (SE) was higher than the summed odds ratios of patients having only tobacco exposure or shared epitope (odds ratios: TE+/SE−, 1.07; TE−/SE+, 2.49; and TE+/SE+, 5.27—all relative to TE−/SE−). A similar effect was found for RF, but stratification showed that the interaction primarily associated with the anti-CCP antibody response. In patients with undifferentiated arthritis at two weeks, or with persistent undifferentiated arthritis after one year, no interaction between tobacco exposure and shared epitope was observed for the presence of autoantibodies. Conclusions: Tobacco exposure increases the risk factor for anti-CCP antibodies only in shared epitope positive patients with rheumatoid arthritis. The gene–environment interaction between smoking and shared epitope leading to autoantibodies is specific for rheumatoid arthritis and is not observed in undifferentiated arthritis.

Identification of new susceptibility loci for osteoarthritis (arcOGEN): A genome-wide association study

Summary Background Osteoarthritis is the most common form of arthritis worldwide and is a major cause of pain and disability in elderly people. The health economic burden of osteoarthritis is increasing commensurate with obesity prevalence and longevity. Osteoarthritis has a strong genetic component but the success of previous genetic studies has been restricted due to insufficient sample sizes and phenotype heterogeneity. Methods We undertook a large genome-wide association study (GWAS) in 7410 unrelated and retrospectively and prospectively selected patients with severe osteoarthritis in the arcOGEN study, 80% of whom had undergone total joint replacement, and 11 009 unrelated controls from the UK. We replicated the most promising signals in an independent set of up to 7473 cases and 42 938 controls, from studies in Iceland, Estonia, the Netherlands, and the UK. All patients and controls were of European descent. Findings We identified five genome-wide significant loci (binomial test p≤5·0×10−8) for association with osteoarthritis and three loci just below this threshold. The strongest association was on chromosome 3 with rs6976 (odds ratio 1·12 [95% CI 1·08–1·16]; p=7·24×10−11), which is in perfect linkage disequilibrium with rs11177. This SNP encodes a missense polymorphism within the nucleostemin-encoding gene GNL3. Levels of nucleostemin were raised in chondrocytes from patients with osteoarthritis in functional studies. Other significant loci were on chromosome 9 close to ASTN2, chromosome 6 between FILIP1 and SENP6, chromosome 12 close to KLHDC5 and PTHLH, and in another region of chromosome 12 close to CHST11. One of the signals close to genome-wide significance was within the FTO gene, which is involved in regulation of bodyweight—a strong risk factor for osteoarthritis. All risk variants were common in frequency and exerted small effects. Interpretation Our findings provide insight into the genetics of arthritis and identify new pathways that might be amenable to future therapeutic intervention. Funding arcOGEN was funded by a special purpose grant from Arthritis Research UK.

Association between weight or body mass index and hand osteoarthritis: a systematic review

Objective To investigate the association between weight or body mass index (BMI) and the development of hand osteoarthritis. Methods Systematic review of observational studies. Medical databases were searched up to April 2008. Articles that presented data on the association between weight and hand osteoarthritis were selected. The qualities of these studies were then assessed by two independent reviewers using a 19 criteria scoring system. Using the mean scores of all studies as a cut-off value, the studies were deemed as high or low quality. Study quality and study designs were combined to determine the level of evidence using best-evidence synthesis, which consisted of five levels of evidence. Results From the 25 studies included, two had cohort, three case–control and 20 cross-sectional study designs. Fifteen studies were considered high-quality studies. Of these high-quality studies, one cohort, two case–control and seven cross-sectional studies showed a positive association between weight or BMI and hand osteoarthritis. Based on three high-quality studies with preferred study designs (one cohort and two case–control) with a positive association, the level of evidence of the association between overweight and developing hand osteoarthritis is moderate. The approximate risk ratio of this association is 1.9. Conclusion Weight or BMI is associated with the development of hand osteoarthritis. The level of evidence of published studies is moderate according to best-evidence synthesis. Further high-quality cohort or case–control studies are needed to elucidate the role of weight in hand osteoarthritis.

Synovial inflammation, immune cells and their cytokines in osteoarthritis: a review.

OBJECTIVE Although osteoarthritis (OA) is considered a non-inflammatory condition, it is widely accepted that synovial inflammation is a feature of OA. However, the role of immune cells and their cytokines in OA is largely unknown. This narrative systematic review summarizes the knowledge of inflammatory properties, immune cells and their cytokines in synovial tissues (STs) of OA patients. DESIGN Broad literature search in different databases was performed which resulted in 100 articles. RESULTS Of 100 articles 33 solely investigated inflammation in OA ST with or without comparison with normal samples; the remaining primarily focussed on rheumatoid arthritis (RA) ST. Studies investigating different severity stages or cellular source of cytokines were sparse. OA ST displayed mild/moderate grade inflammation when investigated by means of haematoxylin and eosin (H&E) staining. Most frequently found cells types were macrophages, T cells and mast cells (MCs). Overall the number of cells was lower than in RA, although the number of MCs was as high as or sometimes even higher than in RA ST. Cytokines related to T cell or macrophage function were found in OA ST. Their expression was overall higher than in normal ST, but lower than in RA ST. Their cellular source remains largely unknown in OA ST. CONCLUSION Inflammation is common in OA ST and characterized by immune cell infiltration and cytokine secretion. This inflammation seems quantitatively and qualitatively different from inflammation in RA. Further research is needed to clarify the role of inflammation, immune cells and their cytokines in the pathogenesis of OA.

Do knee abnormalities visualised on MRI explain knee pain in knee osteoarthritis? A systematic review

Objective To systematically evaluate the association between MRI findings (cartilage defects, bone marrow lesions (BML), osteophytes, meniscal lesion, effusion/synovitis, ligamentous abnormalities, subchondral cysts and bone attrition) and pain in patients with knee osteoarthritis (OA) in order to establish the relevance of such findings when assessing an individual patient. Methods The Medline, Web of Science, Embase and Cumulative Index to Nursing & Allied Health Literature (CINAHL) databases up to March 2010 were searched without language restriction to find publications with data on the association between MRI findings of knee OA (exposure of interest) and knee pain (outcome). The quality of included papers was scored using a predefined criteria set. The levels of evidence were determined qualitatively using best evidence synthesis (based on guidelines on systematic review from the Cochrane Collaboration Back Review Group). Five levels of evidence were used: strong, moderate, limited, conflicting and no evidence. Results A total of 22 papers were included; 5 had longitudinal and 17 cross-sectional data. In all, 13 reported a single MRI finding and 9 multiple MRI findings. Moderate levels of evidence were found for BML and effusion/synovitis. The OR for BML ranged from 2.0 (no CI was given) to 5.0 (2.4 to 10.5). The OR of having pain when effusion/synovitis was present ranged between 3.2 (1.04 to 5.3) and 10.0 (1.1 to 149). The level of evidences between other MRI findings and pain were limited or conflicting. Conclusions Knee pain in OA is associated with BML and effusion/synovitis suggesting that these features may indicate the origin of pain in knee OA. However, due to the moderate level of evidence these features need to be explored further.

A Genome-Wide Association Study Identifies an Osteoarthritis Susceptibility Locus on Chromosome 7q22

OBJECTIVE To identify novel genes involved in osteoarthritis (OA), by means of a genome-wide association study. METHODS We tested 500,510 single-nucleotide polymorphisms (SNPs) in 1,341 Dutch Caucasian OA cases and 3,496 Dutch Caucasian controls. SNPs associated with at least 2 OA phenotypes were analyzed in 14,938 OA cases and approximately 39,000 controls. Meta-analyses were performed using the program Comprehensive Meta-analysis, with P values <1 x 10(-7) considered genome-wide significant. RESULTS The C allele of rs3815148 on chromosome 7q22 (minor allele frequency 23%; intron 12 of the COG5 gene) was associated with a 1.14-fold increased risk (95% confidence interval 1.09-1.19) of knee and/or hand OA (P = 8 x 10(-8)) and also with a 30% increased risk of knee OA progression (95% confidence interval 1.03-1.64) (P = 0.03). This SNP is in almost complete linkage disequilibrium with rs3757713 (68 kb upstream of GPR22), which is associated with GPR22 expression levels in lymphoblast cell lines (P = 4 x 10(-12)). Immunohistochemistry experiments revealed that G protein-coupled receptor protein 22 (GPR22) was absent in normal mouse articular cartilage or synovium. However, GPR22-positive chondrocytes were found in the upper layers of the articular cartilage of mouse knee joints that were challenged with in vivo papain treatment or methylated bovine serum albumin treatment. GPR22-positive chondrocyte-like cells were also found in osteophytes in instability-induced OA. CONCLUSION Our findings identify a novel common variant on chromosome 7q22 that influences susceptibility to prevalence and progression of OA. Since the GPR22 gene encodes a G protein-coupled receptor, this is potentially an interesting therapeutic target.

Large‐scale analysis of association between GDF5 and FRZB variants and osteoarthritis of the hip, knee, and hand

OBJECTIVE GDF5 and FRZB have been proposed as genetic loci conferring susceptibility to osteoarthritis (OA); however, the results of several studies investigating the association of OA with the rs143383 polymorphism of the GDF5 gene or the rs7775 and rs288326 polymorphisms of the FRZB gene have been conflicting or inconclusive. To examine these associations, we performed a large-scale meta-analysis of individual-level data. METHODS Fourteen teams contributed data on polymorphisms and knee, hip, and hand OA. For rs143383, the total number of cases and controls, respectively, was 5,789 and 7,850 for hip OA, 5,085 and 8,135 for knee OA, and 4,040 and 4,792 for hand OA. For rs7775, the respective sample sizes were 4,352 and 10,843 for hip OA, 3,545 and 6,085 for knee OA, and 4,010 and 5,151 for hand OA, and for rs288326, they were 4,346 and 8,034 for hip OA, 3,595 and 6,106 for knee OA, and 3,982 and 5,152 for hand OA. For each individual study, sex-specific odds ratios (ORs) were calculated for each OA phenotype that had been investigated. The ORs for each phenotype were synthesized using both fixed-effects and random-effects models for allele-based effects, and also for haplotype effects for FRZB. RESULTS A significant random-effects summary OR for knee OA was demonstrated for rs143383 (1.15 [95% confidence interval 1.09-1.22]) (P=9.4x10(-7)), with no significant between-study heterogeneity. Estimates of effect sizes for hip and hand OA were similar, but a large between-study heterogeneity was observed, and statistical significance was borderline (for OA of the hip [P=0.016]) or absent (for OA of the hand [P=0.19]). Analyses for FRZB polymorphisms and haplotypes did not reveal any statistically significant signals, except for a borderline association of rs288326 with hip OA (P=0.019). CONCLUSION Evidence of an association between the GDF5 rs143383 polymorphism and OA is substantially strong, but the genetic effects are consistent across different populations only for knee OA. Findings of this collaborative analysis do not support the notion that FRZB rs7775 or rs288326 has any sizable genetic effect on OA phenotypes.

The infrapatellar fat pad of patients with osteoarthritis has an inflammatory phenotype

Objectives Obesity is a risk factor for the development of osteoarthritis (OA) in hands and knees. Adipose tissue can secrete different adipokines with powerful immunomodulatory effects. The infrapatellar fat pad (IFP) is an intra-articular organ in the vicinity of the synovium and cartilage. It is hypothesised that IFP-derived soluble factors could contribute to pathological processes in the knee joint. A study was therefore undertaken to compare the release of inflammatory mediators in the IFP and subcutaneous adipose tissue (ScAT) and to characterise the adipocytes and immune cell infiltrate in these tissues. Methods Paired IFP and ScAT samples were obtained from 27 patients with primary OA. The stromal vascular cell fraction (SVF) was isolated and characterised by fluorescence activated cell sorting. Cytokine and adipokine release in fat- and adipocyte-conditioned media was measured by luminex. Results IFP secreted higher levels of inflammatory mediators such as interleukin 6 (IL-6), adipsin, adiponectin and visfatin than ScAT. This could be due to differences in the phenotype of adipocytes and/or in the composition and phenotype of the SVF cells. IFP adipocyte-conditioned media showed a trend towards more IL-6 and adipsin than ScAT. Moreover, the SVF fraction of IFP contained more cells/g tissue, a lower percentage of T cells and a higher percentage of mast cells than ScAT. In addition, T cells had a predominantly pro-inflammatory phenotype while macrophages had a mixed pro- and anti-inflammatory phenotype in the IFP. Conclusion There are profound differences in secreted inflammatory factors and immune cell composition between the IFP and ScAT. These data indicate that IFP-derived soluble mediators could contribute to pathophysiological processes in the OA knee joint.

What is the evidence for the presence of a therapeutic window of opportunity in rheumatoid arthritis? A systematic literature review

Objective Initiation of DMARD-therapy in the ‘window of opportunity’ is thought to result in a more effective modification of the processes underlying rheumatoid arthritis (RA). We questioned whether this effect is true or hyped and performed a systematic literature review. Methods Medical literature databases up to June 2012 were systematically reviewed for cohort studies and randomised controlled trials reporting outcome data of early RA in relation with symptom duration at treatment initiation. The quality of these studies was assessed by two independent reviewers using a criteria scoring system of 15 items. Studies were dichotomised with the median score (79%) as cut-off. Best-evidence synthesis was applied to determine the level of evidence per outcome category. A meta-analysis was performed on the studies reporting on achieving DMARD-free sustained remission (the reverse of disease persistency). Results Out of 836 screened articles, 18 fulfilled the selection criteria and were not duplicates. Ten were scored as high quality. Remission (various definitions) and radiographic progression were frequently studied outcomes. There was strong evidence for an association between symptom duration and radiographic progression. A meta-analysis on datasets evaluating DMARD-free sustained remission showed that symptom duration was independently associated with such remission; HR 0.989 (95% CI 0.983 to 0.995) per week increase in symptom duration. A moderate level of evidence was observed for other remission outcomes. Conclusions Even when heterogeneity of patients is taken into account, prolonged symptom duration is associated with radiographic progression and a lower chance on DMARD-free sustained remission. These data may support the presence of a ‘window of opportunity’.

Meta-analysis of genome-wide association studies confirms a susceptibility locus for knee osteoarthritis on chromosome 7q22

Objectives Osteoarthritis (OA) is the most prevalent form of arthritis and accounts for substantial morbidity and disability, particularly in older people. It is characterised by changes in joint structure, including degeneration of the articular cartilage, and its aetiology is multifactorial with a strong postulated genetic component. Methods A meta-analysis was performed of four genome-wide association (GWA) studies of 2371 cases of knee OA and 35 909 controls in Caucasian populations. Replication of the top hits was attempted with data from 10 additional replication datasets. Results With a cumulative sample size of 6709 cases and 44 439 controls, one genome-wide significant locus was identified on chromosome 7q22 for knee OA (rs4730250, p=9.2×10−9), thereby confirming its role as a susceptibility locus for OA. Conclusion The associated signal is located within a large (500 kb) linkage disequilibrium block that contains six genes: PRKAR2B (protein kinase, cAMP-dependent, regulatory, type II, β), HPB1 (HMG-box transcription factor 1), COG5 (component of oligomeric golgi complex 5), GPR22 (G protein-coupled receptor 22), DUS4L (dihydrouridine synthase 4-like) and BCAP29 (B cell receptor-associated protein 29). Gene expression analyses of the (six) genes in primary cells derived from different joint tissues confirmed expression of all the genes in the joint environment.