Rheumatoid arthritis; Treatment; recommendations; American College of Rheumatology; Biologics; DMARD; Disease-modifying anti-rheumatic drug
To study changes in lipid profiles at 24 weeks among early rheumatoid arthritis (RA) patients participating in the Treatment of Early Rheumatoid Arthritis (TEAR) Trial randomized to initiate methotrexate plus etanercept (MTX+ETA), triple therapy (TT) [MTX plus sulfasalazine plus hydroxychloroquine] or aggressively-titrated MTX monotherapy.
The TEAR biorepository study had 459 participating patients. Total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) were measured in serum plasma at 0 and 24 weeks.
At 24 weeks, there were statistically significant mean increases in cholesterol levels in the MTX + ETA, TT, and MTX monotherapy arms, the observed increases were 31.4, 28.7 and 30 mg/dL in LDL-C; 19.3, 22.3 and 20.6 mg/dL in HDL-C and 56.8, 53 and 57.3 mg/dL values in TC (p < 0.001 all compared to baseline). There was a statistically significant decrease in TC/HDL-C ratio at 24 weeks in all 3 treatment groups from baseline. There was no difference in any lipid changes between the 3 treatment arms. After multivariable adjustment, change in C-reactive protein was associated with change in LDL-C (p=0.03), HDL-C (p=0.09), and TC (p=0.01), but disease activity score in 28-joints was not. Baseline glucocorticoid use was associated with changes in HDL-C (p=0.03) and TC (p=0.02).
Levels of TC, LDL-C, and HDL-C increased equivalently shortly after initiation of MTX + ETA, TT and MTX monotherapy among early RA patients with active disease participating in a clinical trial. The clinical relevance of short term changes in traditional lipids on cardiovascular outcomes remains to be determined.
rheumatoid arthritis; etanercept; methotrexate; cholesterol; lipoprotein; cardiovascular
To assess if it is better to intensively treat all early RA patients with drug combinations or reserve this for those who do not appropriately respond to methotrexate monotherapy and assess if the combination therapy of methotrexate plus etanercept is superior to the combination of methotrexate plus sulfasalazine plus hydroxychloroquine.
The TEAR study is a 2-year, randomized, double-blind trial. Using a 2×2 factorial design, participants were randomized to one of four treatment arms: immediate combination therapy of methotrexate plus etanercept; or oral triple therapy (methotrexate plus sulfasalazine plus hydroxychloroquine); or initial methotrexate monotherapy with a step-up to one of the combination therapies (all arms included matching placebos). The primary outcome was an observed-group analysis of DAS28-ESR scores from weeks 48 to 102.
At the week 24 step-up period, those receiving immediate combination therapy (etanercept plus methotrexate; or triple therapy) demonstrated greater reduction in DAS28-ESR compared to those on initial methotrexate monotherapy (DAS28-ESR: 3.6 vs. 4.6, p<0.0001), with no differences between regimens of combination therapy. For weeks 48 through 102, participants randomized to step-up arms had a DAS28-ESR clinical response that was not different than those who received initial combination therapy, regardless of the treatment arm (3.2 vs. 3.2, p=0.75). There was no significant difference in DAS28-ESR between participants receiving oral triple therapy versus combination methotrexate plus etanercept (3.1 vs. 3.2, p=0.42). By week 102, there was a small, statistically significant difference in change in radiographic measurements from baseline between methotrexate plus etanercept compared to oral triple therapy (0.64 vs. 1.69, p= 0.047). The absolute difference at week 102 was small.
There were no differences in the mean DAS28-ESR during weeks 48-102 between participants randomized to methotrexate plus etanercept or triple therapy, regardless of whether they received immediate combination treatment or step-up from methotrexate monotherapy. At 24 months, immediate combination treatment with either strategy was more effective than methotrexate monotherapy prior to step-up. Initial use of methotrexate monotherapy with the addition of sulfasalazine plus hydroxychloroquine; or etanercept, if necessary after 6 months, is a reasonable therapeutic strategy for early RA. The combination of etanercept plus methotrexate resulted in a statistically significant, but clinically small, radiographic benefit over oral triple therapy.
To investigate the associations of alcohol consumption and radiographic disease progression in African Americans with recently diagnosed rheumatoid arthritis (RA).
RA patients included in the study were participants in the Consortium for the Longitudinal Evaluation of African Americans with Early Rheumatoid Arthritis (CLEAR) registry. Patients were categorized based on self-reported alcohol consumption; those consuming < 15 beverages per month versus those with ≥ 15 per month. Association of radiographic disease progression over a one to three year period of observation with alcohol consumption was evaluated using multivariate generalized estimating equations.
There were 166 patients included in the study, 39% reported that they had never consumed alcohol. Of the 61% who had consumed alcohol, 73% reported that they on average consumed less than 15 alcoholic beverages per month and 27% reported consuming ≥ 15 per month. In multivariate analysis, consumption of ≥ 15 alcoholic beverages per month was associated with an increased risk of radiographic disease progression (p = 0.017). There was no evidence of a relationship in those consuming < 15 beverages per month (p = 0.802).
There appears to be a dose-dependent relationship between alcohol use and radiographic disease progression in RA. Individuals who consume 15 or more alcoholic beverages per month may have accelerated rates of radiographic joint damage than with lower levels of consumption.
Rheumatoid Arthritis; alcohol consumption; disease severity; disease activity
The Disease Activity Score based on 28 joints (DAS28) has been increasingly used in clinical practice and research studies of rheumatoid arthritis (RA). Studies have reported discordance between DAS28 based on erythrocyte sedimentation rate (ESR) versus C-reactive protein (CRP) in RA patients. However such comparison is lacking in African-Americans with RA.
This analysis included participants from the Consortium for the Longitudinal Evaluation of African Americans with Early Rheumatoid Arthritis (CLEAR) Registry which enrolls self-declared African-Americans with RA. Using tender and swollen joint counts separate ESR-based and CRP-based DAS28 scores (DAS28-ESR3 and DAS28-CRP3) were calculated, as were DAS28-ESR4 and DAS28-CRP4, which included the patient’s assessment of disease activity. The scores were compared using paired t-test, simple agreement and kappa, correlation coefficient and Bland-Altman plots.
Of the 233 included participants, 85% were women, mean age at enrollment was 52.6 years, and median disease duration at enrollment was 21 months. Mean DAS28-ESR3 was significantly higher than DAS28-CRP3 (4.8 vs. 3.9; p<0.001). Similarly, mean DAS28-ESR4 was significantly higher than DAS28-CRP4 (4.7 vs. 3.9; p<0.001). ESR-based DAS28 remained higher than CRP-based DAS28 even when stratified by age, sex, and disease duration. Overall agreement was not high between DAS28-ESR3 and DAS28-CRP3 (50%) or between DAS28-ESR4 and DAS28-CRP4 (59%). DAS28-CRP3 underestimated disease activity in 47% of the participants relative to DAS28-ESR3 and DAS28-CRP4 in 40% of the participants relative to DAS28-ESR4.
There was significant discordance between the ESR-based and CRP-based DAS28 which could impact clinical treatment decisions in African-Americans with RA.
DAS28; Rheumatoid Arthritis; African-Americans
Racial/ethnic differences with regard to complementary and alternative medicine (CAM) use have been reported in the US. However, specific details of CAM use by African Americans with rheumatoid arthritis (RA) are lacking.
Data were collected from African Americans with RA enrolled in a multicenter registry regarding the use of CAM, including food supplements, topical applications, activities, and alternative care providers. Factors associated with CAM use by sex and disease duration were assessed using t-test, Wilcoxon’s rank sum test, chi-square test, and logistic regression analyses.
Of the 855 participants, 85% were women and mean age at enrollment was 54 years. Overall, ever using any of the CAM treatments, activities, and providers was 95%, 98%, and 51%, respectively (median of 3 for number of treatments, median of 5 for activities, and median of 1 for providers). Those with longer disease duration (>2 years) were significantly more likely (odds ratio >2.0, P < 0.05) to use raisins soaked in vodka/gin, to take fish oils, or to drink alcoholic beverages for RA treatment than those with early disease. As compared to men, women were significantly (P < 0.05) more likely to pray/attend church, write in a journal, and use biofeedback, but were less likely to smoke tobacco or topically apply household oils for treatment of RA.
CAM use was highly prevalent in this cohort, even in individuals with early disease. Health care providers need to be aware of CAM use as some treatments may potentially have interactions with conventional medicines. This could be important within this cohort of African Americans, where racial disparities are known to affect access to conventional care.
Gene polymorphism; methotrexate; rheumatoid arthritis
Integrating genetic data from families with highly penetrant forms of disease together with genetic data from outbred populations represents a promising strategy to uncover the complete frequency spectrum of risk alleles for complex traits such as rheumatoid arthritis (RA). Here, we demonstrate that rare, low-frequency and common alleles at one gene locus, phospholipase B1 (PLB1), might contribute to risk of RA in a 4-generation consanguineous pedigree (Middle Eastern ancestry) and also in unrelated individuals from the general population (European ancestry). Through identity-by-descent (IBD) mapping and whole-exome sequencing, we identified a non-synonymous c.2263G>C (p.G755R) mutation at the PLB1 gene on 2q23, which significantly co-segregated with RA in family members with a dominant mode of inheritance (P = 0.009). We further evaluated PLB1 variants and risk of RA using a GWAS meta-analysis of 8,875 RA cases and 29,367 controls of European ancestry. We identified significant contributions of two independent non-coding variants near PLB1 with risk of RA (rs116018341 [MAF = 0.042] and rs116541814 [MAF = 0.021], combined P = 3.2×10−6). Finally, we performed deep exon sequencing of PLB1 in 1,088 RA cases and 1,088 controls (European ancestry), and identified suggestive dispersion of rare protein-coding variant frequencies between cases and controls (P = 0.049 for C-alpha test and P = 0.055 for SKAT). Together, these data suggest that PLB1 is a candidate risk gene for RA. Future studies to characterize the full spectrum of genetic risk in the PLB1 genetic locus are warranted.
Gene expression profiling may be used to stratify patients by disease severity to test the hypothesis that variable disease outcome has a genetic component. In order to define unique expression signatures in African American rheumatoid arthritis (RA) patients with severe erosive disease, we undertook a gene expression study using samples of RNA from peripheral blood mononuclear cells (PBMCs). RNA from baseline PBMC samples of 96 African American RA patients with early RA (<2 years disease duration) was hybridized to cDNA probes of the Illumina Human HT-V3 expression array. Expression analyses were performed using the ca. 25,000 cDNA probes, and then expression levels were compared to the total number of erosions in radiographs of the hands and feet at baseline and 36 months. Using a false discovery rate cutoff of Q = 0.30, 1,138 genes at baseline and 680 genes at 36 months significantly correlated with total erosions. No evidence of a signal differentiating disease progression, or change in erosion scores between baseline and 36 months, was found. Further analyses demonstrated that the differential gene expression signature was localized to the patients with the most erosive disease (>10 erosions). Ingenuity Pathway Analysis demonstrated that genes with fold change greater than 1.5 implicated immune pathways such as CTLA signaling in cytotoxic T lymphocytes. These results demonstrate that CLEAR patients with early RA having the most severe erosive disease, as compared to more mild cases (<10 erosions), may be characterized by a set of differentially expressed genes that represent biological pathways with relevance to autoimmune disease.
Genome-wide gene expression; Sharp/van der Heijde; Pathway analysis; CLEAR; ABCoN
Cigarette smoking has emerged as a risk factor for development of rheumatoid arthritis (RA). Recent studies have suggested that cigarette smoking may lead to lower treatment response rates with methotrexate (MTX) and some biologic agents in RA. Knowledge of whether tobacco exposure reduces treatment efficacy is important as smoking could represent a modifiable factor in optimizing RA treatment.
Study participants included patients with early RA (<3 years duration) enrolled in the Treatment of Early Aggressive RA (TEAR) trial, a randomized, blinded, placebo-controlled clinical trial (RCT) comparing early intensive therapy (MTX + etanercept or MTX + hydroxychloroquine + sulfasalazine [triple therapy]) versus initial treatment with MTX with step-up to MTX + etanercept or to triple therapy if still active at 24 weeks. Serum cotinine was measured using a commercially available ELISA at baseline and 48 weeks with detectable concentrations at both visits serving as indicator of smoking status. Mean Disease Activity Score (DAS-28) was compared by smoking status, adjusting for baseline disease activity.
Of 412 subjects included in the analysis, 293 (71%) were categorized as ‘non-smokers’ and 119 (29%) as ‘current smokers’. There were no differences in the mean DAS-28 between 48 and 102 weeks based on smoking status for the overall group (p=0.881) or by specific treatment assignment.
Among patients enrolled in a large RCT of early RA with poor prognostic factors, smoking status did not impact treatment responses for those receiving early combination or initial MTX with step-up therapy at 24 weeks if still active.
Methotrexate (MTX) is one of the most commonly prescribed and most effective drugs for the treatment of rheumatoid arthritis (RA). Given the partial response of many patients and the side effect profile of the drug, there is considerable interest in identification of biomarkers to guide MTX therapy in RA. Upon entering cells, MTX is polyglutamated. Measuring methotrexate polyglutamates (MTX PGs) levels in circulating red blood cells (RBC) has been proposed as an objective measure that can help to optimize MTX therapy in RA. There is conflicting data with regard to the clinical utility of measurement of MTX PGs measurements as a predictor of the efficacy or toxicity of low-dose MTX effects in RA. Should large, randomized clinical trials of this assay show consistent, reproducible, long-term correlations between MTX PG levels and efficacy and toxicity, this test could become a prominent tool for clinicians to optimize the use of MTX in RA.
Rheumatoid Arthritis; Methotrexate; Polyglutamates
Etanercept is one of several TNF inhibitors approved for rheumatoid arthritis (RA) and a variety of other immune-mediated inflammatory conditions. Given the plethora of drugs approved for RA and the wide variations in cost and treatment response, markers of efficacy would be very useful. Several candidate genes, including HLA-DRB1 alleles and those encoding TNF, TNF receptors, and Fc receptors, have been examined for a role in the response to treatment with etanercept. In this review, we discuss pharmacogenetic studies of etanercept in RA and other diseases, and comment on the future of such analyses to advance the goal of personalized medicine in RA.
To determine whether shared epitope (SE)–containing HLA–DRB1 alleles are associated with rheumatoid arthritis (RA) in African Americans and whether their presence is associated with higher degrees of global (genome-wide) genetic admixture from the European population.
In this multicenter cohort study, African Americans with early RA and matched control subjects were analyzed. In addition to measurement of serum anti–cyclic citrullinated peptide (anti-CCP) antibodies and HLA–DRB1 genotyping, a panel of >1,200 ancestry-informative markers was analyzed in patients with RA and control subjects, to estimate the proportion of European ancestry.
The frequency of SE-containing HLA–DRB1 alleles was 25.2% in African American patients with RA versus 13.6% in control subjects (P = 0.00005). Of 321 patients with RA, 42.1% had at least 1 SE-containing allele, compared with 25.3% of 166 control subjects (P = 0.0004). The mean estimated percent European ancestry was associated with SE-containing HLA–DRB1 alleles in African Americans, regardless of disease status (RA or control). As reported in RA patients of European ancestry, there was a significant association of the SE with the presence of the anti-CCP antibody: 86 (48.9%) of 176 patients with anti-CCP antibody–positive RA had at least 1 SE allele, compared with 36 (32.7%) of 110 patients with anti-CCP antibody–negative RA (P = 0.01, by chi-square test).
HLA–DRB1 alleles containing the SE are strongly associated with susceptibility to RA in African Americans. The absolute contribution is less than that reported in RA among populations of European ancestry, in which ~50–70% of patients have at least 1 SE allele. As in Europeans with RA, the SE association was strongest in the subset of African American patients with anti-CCP antibodies. The finding of a higher degree of European ancestry among African Americans with SE alleles suggests that a genetic risk factor for RA was introduced into the African American population through admixture, thus making these individuals more susceptible to subsequent environmental or unknown factors that trigger the disease.
Rapidly predicting future outcomes based upon short-term clinical response would be helpful to optimize RA management in early disease.
To derive and validate a clinical prediction rule to predict low disease activity (LDA) at 1 year among patients participating in the Treatment of Early Aggressive Rheumatoid Arthritis (TEAR) trial escalating RA therapy by adding either etanercept (E) or sulfasalazine + hydroxychloroquine [triple therapy (TT)] after 6 months of methotrexate (MTX) therapy.
Eligible subjects included in the derivation cohort (used for model building, n=186) were participants with moderate or higher disease activity (DAS28ESR>3.2) despite 24 weeks of MTX monotherapy who added either etanercept or sulfasalazine+hydroxychloroquine. Clinical characteristics measured within the next 12 weeks were used to predict LDA 1 year later using multivariable logistic regression. Validation was performed in the cohort of TEAR patients randomized to initially receive either MTX+E or TT.
The derivation cohort yielded three prediction models of varying complexity that included age, DAS28 at various time points, body mass index, and ESR (AUROC up to 0.83). Accuracy of the prediction models ranged between 80 and 95% in both derivation and validation cohorts, depending on the complexity of the model and the cutpoints chosen for response and non-response. Approximately 80% of patients could be predicted to be responders or non-responders at week 12.
Clinical data collected early after starting or escalating DMARD/biologic treatment could accurately predict LDA at 1 year in early RA patients. For patients predicted to be non-responders, treatment could be changed at 12 weeks to optimize outcomes.
rheumatoid arthritis; prediction; anti-TNF; triple therapy
Anti–tumor necrosis factor α (anti-TNF) therapy is a mainstay of treatment in rheumatoid arthritis (RA). The aim of the present study was to test established RA genetic risk factors to determine whether the same alleles also influence the response to anti-TNF therapy.
A total of 1,283 RA patients receiving etanercept, infliximab, or adalimumab therapy were studied from among an international collaborative consortium of 9 different RA cohorts. The primary end point compared RA patients with a good treatment response according to the European League Against Rheumatism (EULAR) response criteria (n = 505) with RA patients considered to be nonresponders (n = 316). The secondary end point was the change from baseline in the level of disease activity according to the Disease Activity Score in 28 joints (ΔDAS28). Clinical factors such as age, sex, and concomitant medications were tested as possible correlates of treatment response. Thirty-one single-nucleotide polymorphisms (SNPs) associated with the risk of RA were genotyped and tested for any association with treatment response, using univariate and multivariate logistic regression models.
Of the 31 RA-associated risk alleles, a SNP at the PTPRC (also known as CD45) gene locus (rs10919563) was associated with the primary end point, a EULAR good response versus no response (odds ratio [OR] 0.55, P = 0.0001 in the multivariate model). Similar results were obtained using the secondary end point, the ΔDAS28 (P = 0.0002). There was suggestive evidence of a stronger association in autoantibody-positive patients with RA (OR 0.55, 95% confidence interval [95% CI] 0.39–0.76) as compared with autoantibody-negative patients (OR 0.90, 95% CI 0.41–1.99).
Statistically significant associations were observed between the response to anti-TNF therapy and an RA risk allele at the PTPRC gene locus. Additional studies will be required to replicate this finding in additional patient collections.
We previously reported an analysis of single nucleotide polymorphisms (SNPs) in three validated European rheumatoid arthritis (RA) susceptibility loci, TAGAP, TNFAIP3, and CCR6 in African-Americans with RA. Unexpectedly, the disease-associated alleles were different in African-Americans than in Europeans. In an effort to better define their contribution, we performed additional SNP genotyping in these genes.
Seven SNPs were genotyped in 446 African Americans with RA and 733 African American controls. Differences in minor allele frequency between cases and controls were analyzed after controlling for global proportion of European admixture, and pairwise linkage disequilibrium (LD) was estimated among the SNPs.
Three SNPs were significantly associated with RA: TNFAIP3 rs719149 A allele (OR (95% CI) 1.22 (1.03–1.44) (p =0.02); TAGAP rs1738074 G allele OR 0.75 (0.63–0.89), (p =0.0012); and TAGAP rs4709267 G allele 0.74 (0.60–0.91), (p =0.004). Pairwise LD between the TAGAP SNPs was low (R2=0.034). The haplotype containing minor alleles for both TAGAP SNPs was uncommon (4.5%). After conditional analysis on each TAGAP SNP, its counterpart remained significantly associated with RA (rs1738074 for rs4709267 p=0.00001; rs4709267 for rs1738074 p=0.00005), suggesting independent effects.
SNPs in regulatory regions of TAGAP and an intronic SNP (TNFAIP3) are potential susceptibility loci in African Americans. Pairwise LD, haplotype analysis, and SNP conditioning analysis suggest that these two SNPs in TAGAP are independent susceptibility alleles. Additional fine mapping of this gene and functional genomic studies of these SNPs should provide additional insight into the role of these genes in RA.
To examine whether polymorphisms in genes coding for drug metabolizing enzymes (DMEs) impact rheumatoid arthritis (RA) risk due to cigarette smoking in African Americans.
Smoking status was evaluated in African American RA cases and non-RA controls categorized as heavy (≥ 10 pack-years) vs. other. Individuals were genotyped for a homozygous deletion polymorphism in glutathione S-transferase Mu-1 (GSTM1-null) in addition to tagging single nucleotide polymorphisms (SNPs) in N-acetyltransferase (NAT)1, NAT2, and epoxide hydrolase (EPXH1). Associations of genotypes with RA were examined using logistic regression and gene-smoking interactions were assessed.
There were no significant associations of any DME genotype with RA. After adjustment for multiple comparisons, there were significant additive interactions between heavy smoking and NAT2 SNPs rs9987109 (Padd = 0.000003) and rs1208 (Padd = 0.00001); attributable proportions (APs) due to interaction ranged from 0.61 to 0.67. None of the multiplicative gene-smoking interactions examined remained significant after adjustment for multiple testing in overall disease risk. There was no evidence of significant gene-smoking interactions in analyses of GSTM1-null, NAT1, or EPXH1. DME gene-smoking interactions were similar when cases were limited to anti-citrullinated protein antibody (ACPA) positive individuals.
Among African Americans, RA risk imposed by heavy smoking appears to be mediated in part by genetic variation in NAT2. While further studies are needed to elucidate mechanisms underpinning these interactions, these SNPs appear to identify African American smokers at a much higher risk for RA with relative risks that are at least two-fold higher compared to non-smokers lacking these risk alleles.
rheumatoid arthritis; African Americans; cigarette smoking; anti-CCP antibody; drug metabolizing enzyme; N-acetyltransferase; epoxide hydrolase; glutathione S-transferase
Large-scale genetic association studies have identified over 20 rheumatoid arthritis (RA) risk alleles among individuals of European ancestry. The influence of these risk alleles has not been comprehensively studied in African-Americans. We therefore sought to examine whether these validated RA risk alleles are associated with RA in an African-American population.
27 candidate SNPs were genotyped in 556 autoantibody-positive African-Americans with RA and 791 healthy African-American controls. Odds ratios (OR) and 95% confidence intervals (CI) for each SNP were compared to previously published ORs of RA patients of European ancestry. We then calculated a composite Genetic Risk Score (GRS) for each individual based on the sum of all risk alleles.
There was overlap in the OR and 95% CI between the European and African-American populations in 24 of the 27 candidate SNPs. Conversely, 3 of the 27 SNPs (CCR6 rs3093023, TAGAP rs394581, TNFAIP3 rs6920220) demonstrated an OR in the opposite direction from those reported in RA patients of European ancestry. The GRS analysis indicated a small but highly significant probability that African-American cases were enriched for the European RA risk alleles relative to controls (p=0.00005).
The majority of RA risk alleles previously validated among European ancestry RA patients showed similar ORs in our population of African-Americans with RA. Furthermore, the aggregate GRS supports the hypothesis that these SNPs are risk alleles for RA in the African-American population. Future large-scale genetic studies are needed to validate these risk alleles and identify novel risk alleles for RA in African-Americans.
To examine the associations of cigarette smoking with rheumatoid arthritis (RA) in African Americans and to determine to whether this association is impacted by HLA-DRB1 shared epitope (SE).
Smoking status, cumulative smoking exposure, and SE status were measured in African American patients with RA and in healthy controls. Associations of smoking with RA were examined using age- and gender-adjusted logistic regression. Additive and multiplicative SE-smoking interactions were examined.
After adjusting for age and gender, ever (OR = 1.45; 95% CI 1.07 to 1.97) and current smoking (OR = 1.56; 95% CI 1.07 to 2.26) were more common in African American RA cases (n = 605) than in controls (n = 255). The association of smoking with RA was limited to those with a cumulative exposure exceeding 10 pack-years, associations that were evident in both autoantibody positive and negative disease. There was evidence of a significant additive interaction between SE status and heavy smoking (≥ 10 pack-years) in RA risk (attributable proportion due to interaction [AP] of 0.58, p = 0.007) with an AP of 0.47 (p = 0.006) between SE status and ever smoking. There was no evidence of multiplicative interactions.
Among African Americans, cigarette smoking is associated not only with the risk of autoantibody positive RA but also with the risk of autoantibody negative disease. RA risk attributable to smoking is limited to African Americans with more than 10 pack-years of exposure and is more pronounced among individuals positive for HLA-DRB1 SE.
rheumatoid arthritis; African Americans; cigarette smoking; rheumatoid factor; anti-CCP antibody; HLA-DRB1 shared epitope
We previously reported association of co-occurrence of HLA-DRB1 shared epitope (SE) and RANKL SNPs with younger age of RA onset in 182 rheumatoid factor positive (RF) European American (EA) early RA patients. Here, we fine-mapped the 48 kb RANKL region in the extended 210 EA RF-positive early RA cohort, sought replication of RA-associated SNPs in additional 501 EA and 298 African-Americans (AA) RA cohorts, and explored functional consequences of RA-associated SNPs.
SNP genotyping was conducted using pyrosequencing or TaqMan PCR assays. Associations of rs7984870 with RANKL expression in plasma, PBMC and isolated T cells were quantified using ELISA and RT-PCR. Site-directed mutagenesis of rs7984870 within the 2kb RANKL promoter was performed to drive the luciferase reporter gene in osteoblast and stromal cell lines. Interaction of DNA and protein was determined by electrophoretic mobility shift assay.
A single promoter SNP rs7984870 was consistently significantly associated with earlier age of RA onset in 3 independent seropositive (RF or anti-cyclic citrullinated peptide antibody positive) RA cohorts but not in seronegative RA patients. The risk C allele of rs7984870 conferred 2-fold higher plasma RANKL levels in RF-positive RA patients, significantly elevated RANKL mRNA expression in activated normal T cells, and increased promoter activity after stimulation in vitro via differential binding to transcription factor SOX5.
The RANKL promoter allele that increased transcriptional levels upon stimulation might promote interaction between activated T cells and dendritic cells, predisposing to younger RA onset in seropositive EA and/or AA individuals.
Multiple sclerosis (MS) is a common demyelinating disease of the central nervous system mediated by autoimmune and neurodegenerative pathogenic mechanisms. Multiple genes account for its moderate heritability, but the only genetic region shown to have a large replicable effect on MS susceptibility is the major histocompatibility complex (MHC). Strong linkage disequilibrium (LD) across the MHC has made it difficult to fully characterize individual genetic contributions of this region to MS risk in previous studies. African Americans are at a lower risk for MS when compared with northern Europeans and Americans of European descent, but greater haplotypic diversity and distinct patterns of LD suggest that this population may be particularly informative for fine-mapping efforts. To examine the role of the MHC in African American MS, a case–control association study was performed with 499 African American MS patients and 750 African American controls that were genotyped for 6040 MHC region single nucleotide polymorphisms (SNPs). A replication data set consisting of 451 African American patients and 718 African American controls was genotyped for selected SNPs. Two MHC class II SNPs, rs2647040 and rs3135021, were significant in the replication cohort and partially tagged DRB1*15 alleles. Surprisingly, in comparison to similar studies of individuals of European descent, the MHC seems to play a smaller role in MS susceptibility in African Americans, consistent with pervasive genetic heterogeneity across ancestral groups, and may explain the difference in MS susceptibility between African Americans and individuals of European descent.