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1.  Association of anti-peptidyl arginine deiminase antibodies with radiographic severity of rheumatoid arthritis in African Americans 
Evidence suggests that the presence of peptidyl arginine deiminase type 4 (PAD4) antibodies is associated with radiographic-severity rheumatoid arthritis (RA) among Caucasian patients. The presence of anti-PAD4 antibodies that were cross-reactivity against PAD3 was associated with more aggressive erosive disease (compared with the presence of anti-PAD4 antibodies without anti-PAD3 crossreactivity) in Caucasian RA patients. The objectives of this study were to determine the prevalence of serum anti-PAD4 and anti-PAD4/PAD3 cross-reactive autoantibodies in African Americans with RA and whether these antibodies associate with radiographic severity and radiographic progression.
Serum anti-PAD4 and anti-PAD4/PAD3 antibodies were measured by immunoprecipitation, and the temporal trends in titers were analyzed. We compared total radiographic scores among anti-PAD4-positive, anti-PAD4/PAD3-positive, and anti-PAD4-negative patients and used a zero-inflated negative binomial model to determine associations between radiographic severity and antibody status. Logistic regression was used to analyze radiographic progression.
Of 192 African-American patients with RA, 73 % were anti-citrullinated peptide/protein antibody (ACPA)-positive, 46 out of 192 (24 %) of whom had serum anti-PAD4 antibodies. Median (interquartile range) total Sharp van der Heijde radiographic scores were 2 (1–97.5) in ACPA-positive patients and 0 (0–3) in ACPA-negative patients (P < 0.001). Of the 46 anti-PAD4-positive patients, 20 had anti-PAD4 antibodies that cross-reacted with PAD3. In patients with early RA, anti-PAD4 and anti-PAD4/PAD3 antibody titers increased over time (P = 0.006, P = 0.001, respectively). Median (interquartile range) total radiographic scores were higher for anti-PAD4-positive than for anti-PAD4-negative patients (3 (1–115) versus 2 (0–11), respectively; P = 0.005). Median (interquartile range) total radiographic score for anti-PAD4/PAD3-positive patients was 76 (3–117) (P < 0.001) versus anti-PAD4-negative patients. Only anti-PAD4/PAD3 antibodies associated with radiographic severity (incidence rate ratio = 2.81; 95 % confidence interval 1.23, 6.43).
This analysis suggests that autoantibodies against PAD4 and PAD3 proteins may serve as biomarkers for identifying African-American patients with RA and higher radiographic severity.
Electronic supplementary material
The online version of this article (doi:10.1186/s13075-016-1126-7) contains supplementary material, which is available to authorized users.
PMCID: PMC5075170  PMID: 27770831
Anti-PAD4; Rheumatoid arthritis; Radiographic severity; African American
2.  The Role of Genetic Variants in CRP in Radiographic Severity in African Americans with Early and Established Rheumatoid Arthritis 
Genes and immunity  2015;16(7):446-451.
This study investigates the association of CRP single nucleotide polymorphisms (SNPs) with plasma CRP levels and radiographic severity in African Americans with early and established rheumatoid arthritis (RA). Using a cross-sectional case-only design, CRP SNPs were genotyped in two independent sets of African Americans with RA: Consortium for the Longitudinal Evaluation of African Americans with RA (CLEAR 1) and CLEAR 2. Radiographic data and CRP measurements were available in 294 individuals from CLEAR 1 [median (IQR 25-75) disease duration of 1 (0.6-1.6) year] and in 407 persons from CLEAR 2 [median (IQR 25-75) disease duration of 8.9 (3.5 – 17.7) years]. In CLEAR 1, in adjusted models, the minor allele of rs2808630 was associated with total radiographic score [incident rate ratio (IRR) 0.37 (95% CI 0.19-0.74), p value =0.0051]. In CLEAR 2, the minor allele of rs3093062 was associated with increased plasma CRP levels (p value =0.002). For each rs3093062 minor allele, the plasma CRP increased by 1.51 (95% CI 1.15-1.95) mg/dL when all the other covariates remained constant. These findings have important implications for assessment of the risk of joint damage in African Americans with RA.
PMCID: PMC4707038  PMID: 26226010
C reactive protein; genetics; rheumatoid arthritis; joint damage; radiography
3.  Expression of Interferon-gamma Receptor Genes in PBMCs is Associated with Rheumatoid Arthritis and Its Radiographic Severity in African Americans 
Factors responsible for radiographic severity of rheumatoid arthritis (RA) in African-Americans are poorly understood. We sought to identify genes whose expression in peripheral blood mononuclear cells (PBMCs) is associated with radiographic severity of RA.
We initially performed quantitative real-time (qRT)-PCR for 182 genes based on plausible immune pathways in 40 African-American RA patients with extremes of radiographic damage (low versus high radiographic scores) and disease duration (early versus late) and 20 healthy African-American controls. In the second phase, we analyzed the expression of significantly associated candidate genes (IFNGR2 and its biological partner IFNGR1) with radiographic scores in 576 African-American RA patients and 51 controls not previously analyzed, accounting for autoantibody status and disease duration.
We found significant differences in IFNGR1 expression between RA and controls (P=6 × 10−14) and in IFNGR2 expression between those with erosions vs no erosions (P=0.01) (Wilcoxon sum test). We also found A significant correlations between IFNGR2 expression and radiographic scores (P=0.03 for erosions, P=0.04 for joint space narrowing, and P=0.03 for total radiographic score, zero-inflated negative binomial model) and annualized progression rate (P=0.0024, Spearman correlation).
These findings have important implications with respect to IFNγ for the pathogenesis of RA and may lead to identification of a biomarker for radiographic damage. Additional studies are needed to define cell subsets responsible for the association of IFNγ receptor gene expression with radiographic finding, which downstream mechanisms are involved, and generalizability to other RA populations.
PMCID: PMC4414815  PMID: 25708927
4.  HLA-DRB1 rheumatoid arthritis risk in African Americans at multiple levels: Hierarchical classification systems, amino acid positions and residues 
To evaluate African American rheumatoid arthritis HLA-DRB1 genetic risk by three validated allele classification systems, and by amino acid position and residue. To compare the genetic risk between African American and European ancestries.
Four-digit HLA-DRB1 genotyping was performed on 561 autoantibody-positive African American cases and 776 African American controls. Association analysis was performed on Tezenas du Montcel (TdM); de Vries (DV); and Mattey classification system alleles and separately by amino acid position and individual residues.
TdM S2 and S3P alleles were associated with RA (odds ratios (95% CI) 2.8 (2.0, 3.9) and 2.1 (1.7, 2.7), respectively). The DV (P-value=3.2 x 10−12) and Mattey (P-value=6.5 x 10−13) system alleles were both protective in African Americans. Amino acid position 11 (permutation P-value < 0.00001) accounted for nearly all variability explained by HLA-DRB1, although conditional analysis demonstrated that position 57 was also significant (0.01<= permutation P-val <=0.05). The valine and aspartic acid residues at position 11 conferred the highest risk for RA in African Americans.
With some exceptions, the genetic risk conferred by HLA-DRB1 in African Americans is similar to European ancestry at multiple levels: classification system (e.g., TdM), amino acid position (e.g. 11) and residue (Val 11). Unlike that reported from European ancestry, amino acid position 57 was associated with RA in African Americans, but positions 71 and 74 were not. Asp11 (OR = 1 in European ancestry) corresponds to the four digit classical allele, *09:01, also a risk allele for RA in Koreans.
PMCID: PMC4273668  PMID: 25524867
5.  Bisphosphonate-associated osteonecrosis of the jaw, with healing after teriparatide: a review of the literature and a case report 
This paper reports the case history of a patient who had bisphosphonate-associated osteonecrosis of the jaw (ONJ) in which adjunctive treatment with teriparatide was used. The patient was treated for 5 years with alendronate for osteoporosis and developed ONJ after extraction of maxillary teeth. An implant was placed at the site of the extracted teeth. The pathology report confirmed the clinical diagnosis of ONJ; treatment was changed from alendronate to teriparatide and the ONJ resolved. To our knowledge, this is the third case history reported in the literature in which teriparatide was successfully used as adjunct therapy in ONJ because it has an anabolic effect and presumed role in accelerating bone healing. ONJ is a serious but infrequent condition that has been recently associated with nitrogen-containing bisphosphonate therapy.
Teriparatide may be a useful adjunctive therapy when ONJ develops.
PMCID: PMC4097110  PMID: 20415805
6.  Simple regression for correcting ΔCt bias in RT-qPCR low-density array data normalization 
BMC Genomics  2015;16(1):82.
Reverse transcription quantitative PCR (RT-qPCR) is considered the gold standard for quantifying relative gene expression. Normalization of RT-qPCR data is commonly achieved by subtracting the Ct values of the internal reference genes from the Ct values of the target genes to obtain ΔCt. ΔCt values are then used to derive ΔΔCt when compared to a control group or to conduct further statistical analysis.
We examined two rheumatoid arthritis RT-qPCR low density array datasets and found that this normalization method introduces substantial bias due to differences in PCR amplification efficiency among genes. This bias results in undesirable correlations between target genes and reference genes, which affect the estimation of fold changes and the tests for differentially expressed genes. Similar biases were also found in multiple public mRNA and miRNA RT-qPCR array datasets we analysed. We propose to regress the Ct values of the target genes onto those of the reference genes to obtain regression coefficients, which are then used to adjust the reference gene Ct values before calculating ΔCt.
The per-gene regression method effectively removes the ΔCt bias. This method can be applied to both low density RT-qPCR arrays and individual RT-qPCR assays.
Electronic supplementary material
The online version of this article (doi:10.1186/s12864-015-1274-1) contains supplementary material, which is available to authorized users.
PMCID: PMC4335788
RT-PCR; Normalization; ΔCt; Housekeeping genes; Regression
7.  Renal damage is the most important predictor of mortality within the damage index: data from LUMINA LXIV, a multiethnic US cohort 
Rheumatology (Oxford, England)  2009;48(5):542-545.
Objective. Damage accrual in SLE has been previously shown to be an independent predictor of mortality. We sought to discern which SLICC Damage Index (SDI) domains are the most important predictors of survival in SLE.
Methods. SLE patients (ACR criteria), age ⩾16 years, disease duration ⩽5 years at enrolment, of African–American, Hispanic or Caucasian ethnicity were studied. Disease activity was assessed using the SLAM-Revised (SLAM-R) at diagnosis. Damage was ascertained using the SDI at the last visit. The SDI domains associated with time to death (and interaction terms) were examined by univariable and multivariable Cox proportional hazards regression analyses; those significant in the multivariable analyses were added to the final two models (with and without poverty) that included other variables known to be associated with shorter survival.
Results. A total of 635 SLE patients were studied of whom 97 (15.3%) have died over a mean (s.d.) total disease duration of 5.7 (3.7) years. Patients were predominantly women [570 (89.8%)]; their mean (s.d.) age was 36.5 (12.6) years; 126 (19.8%) had developed renal damage, 62 (9.3%) cardiovascular, 48 (7.8%) pulmonary and 34 (5.4%) peripheral vascular damage. When excluding poverty from the multivariable model, the renal domain of the SDI was independently associated with a shorter time to death (hazard ratio = 1.65; 95% CI 1.03, 2.66).
Conclusions. The renal domain of the damage index is associated with a shorter time to death when poverty, a strong predictor of this outcome, is removed from the model. Preventing renal damage in lupus patients has long-term prognostic implications.
PMCID: PMC2722801  PMID: 19233884
Lupus; Renal damage; Mortality; Survival; Cohort; Ethnicity; SLICC damage index
8.  Biologics and heart failure in rheumatoid arthritis: are we any wiser? 
Current opinion in rheumatology  2008;20(3):327-333.
Purpose of review
To summarize the recent literature concerning the role of TNF-a in heart failure, epidemiology of heart failure in rheumatoid arthritis and risk of heart failure associated with biologic disease-modifying antirheumatic drugs in rheumatoid arthritis.
Recent findings
TNF-a has been implicated in the pathogenesis of heart failure. It has direct deleterious effects on the myocardium in the setting of acute injury or chronic heart failure. In animal models, TNF-a is important in cardiac remodeling, leading to cardiac dysfunction following acute injury. Both incident and worsening heart failure have been reported in patients with rheumatoid arthritis who are treated with anti-TNF-a therapy. Recent cohort studies, however, have shown no increased risk and, in some, a protective effect on the risk of heart failure. Certain traditional cardiovascular risk factors have a relatively lesser contribution to cardiovascular morbidity and mortality in patients with rheumatoid arthritis, suggesting that disease-related perturbations of the cytokine network may contribute to the excess risk of heart failure in these patients.
Overall mortality in rheumatoid arthritis has remained stagnant despite advances in rheumatoid arthritis and heart failure management and improved cardiovascular mortality in the general population. Heart failure prevalence is increased in patients with rheumatoid arthritis and leads to greater mortality. Despite current expert consensus contraindicating the use of anti-TNF-a agents in patients with moderate to severe heart failure, epidemiological studies in rheumatoid arthritis have not consistently substantiated this association.
PMCID: PMC4097098  PMID: 18388526
anti-TNF-a agents; biologic disease-modifying antirheumatic drugs; heart failure; rheumatoid arthritis
10.  Measurement of Erythrocyte Methotrexate Polyglutamate Levels: Ready for Clinical Use in Rheumatoid Arthritis? 
Current rheumatology reports  2010;12(5):342-347.
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.
PMCID: PMC3769795  PMID: 20665136
Rheumatoid Arthritis; Methotrexate; Polyglutamates
11.  Pharmacogenetics of Etanercept in Rheumatoid Arthritis 
Pharmacogenomics  2008;9(8):1011-1015.
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.
PMCID: PMC3746504  PMID: 18681777
13.  Radiographic Severity of Rheumatoid Arthritis in African-Americans: Results from the CLEAR Registry 
Arthritis care & research  2010;62(5):624-631.
To describe radiographic changes in African-Americans with rheumatoid arthritis (RA) from the CLEAR (Consortium for the Longitudinal Evaluation of African-Americans with Early Rheumatoid Arthritis) Registry, a multicenter observational study.
Self-declared African-American patients, were enrolled in CLEAR I, a longitudinal cohort of early RA (disease duration <2 years) from 2000 to 2005; or in CLEAR II, a cross-sectional cohort (any disease duration), from 2006 to the present. Demographic and clinical data were obtained, and sets of hand/wrist and foot radiographs were scored using the modified Sharp/van der Heijde scoring system.
A total of 357 and 418 patients, respectively, have been enrolled into CLEAR I and CLEAR II. We report here an interim analysis of radiographic severity in these patients. For the CLEAR I cohort, 294 patients had a mean radiographic score of 2.89 at the baseline visit; 32.0% showed either erosions (25.9%) or joint space narrowing (JSN) (19.4%). At the 36-month visit the mean score was 5.65; 44.2% had erosions, 41.5% JSN and 55.4% had either. Among those patients without radiographic damage at baseline, 18.9% had progressed at the 36-month visit, compared to 57.1% of those with baseline damage (p<0.0001). For the CLEAR II cohort, 167 patients with RA of any duration, 65.3% exhibited joint erosions, 65.3% JSN and 74.8% exhibited either. The mean radiographic score was 33.42.
This is the largest radiographic study of African American RA patients. Damage occurs early in the disease and is associated with radiographic progression at 3 years of disease duration. The CLEAR Registry will provide a valuable resource for future analyses of genetic, clinical, and environmental factors associated with radiographic severity of RA in African-Americans.
PMCID: PMC3052790  PMID: 20461784
14.  Protective Effect of Hydroxychloroquine on Renal Damage in Patients with Lupus Nephritis: Data from LUMINA, a Multiethnic U.S. Cohort 
Arthritis and rheumatism  2009;61(6):830-839.
To assess if hydroxychloroquine can delay renal damage development in lupus nephritis patients.
Lupus nephritis patients (n=256) from LUMINA (n=635), a multiethnic cohort of African Americans, Hispanics and Caucasians, age ≥16 years, disease duration ≤5 years at baseline (T0) were studied. Renal damage was defined per the SLICC Damage Index (≥1 of the following lasting at least six months: estimated/measured glomerular filtration rate <50%, 24-hour proteinuria ≥3.5 g and/or end-stage renal disease, regardless of dialysis or transplantation). Patients with renal damage before T0 were excluded (n=53). The association between hydroxychloroquine use and renal damage (as defined, or omitting proteinuria) was estimated using Cox proportional regression analyses adjusting for potentially confounders. Kaplan-Meier survival curves based on hydroxychloroquine intake or World Health Organization (WHO) Class glomerulonephritis were also derived.
Sixty-three (31.0%) of 203 patients developed renal damage over a mean (standard deviation) disease duration of 5.2 (3.5) years. The most frequent renal damage domain item was proteinuria. Hydroxychloroquine-takers (79.3%) exhibited a lower frequency of WHO Class IV glomerulonephritis, lower disease activity and received lower glucocorticoid doses than non-takers. After adjusting for confounders, hydroxychloroquine was protective of renal damage occurrence in full (HR=0.12; 95% CI 0.02-0.97; p=0.0464) and reduced (HR=0.29; 95%CI 0.13-0.68; p=0.0043) models. Omitting proteinuria provided comparable results. The cumulative probability of renal damage occurrence was higher in hydroxychloroquine non-takers and in WHO Class IV glomerulonephritis (p<0.0001).
After adjusting for possible confounding factors the protective effect of hydroxychloroquine in retarding renal damage occurrence in SLE is still evident.
PMCID: PMC2898742  PMID: 19479701
15.  Association of IL4R single-nucleotide polymorphisms with rheumatoid nodules in African Americans with rheumatoid arthritis 
To determine whether IL4R single-nucleotide polymorphisms (SNPs) rs1805010 (I50V) and rs1801275 (Q551R), which have been associated with disease severity in rheumatoid arthritis (RA) patients of European ancestry, relate to the presence of rheumatoid nodules and radiographic erosions in African Americans.
Two IL4R SNPs, rs1805010 and rs1801275, were genotyped in 749 patients from the Consortium for Longitudinal Evaluation of African-Americans with Early Rheumatoid Arthritis (CLEAR) registries. End points were rheumatoid nodules defined as present either by physical examination or by chest radiography and radiographic erosions (radiographs of hands/wrists and feet were scored using the modified Sharp/van der Heijde system). Statistical analyses were performed by using logistic regression modeling adjusted for confounding factors.
Of the 749 patients with RA, 156 (20.8%) had rheumatoid nodules, with a mean age of 47.0 years, 84.6% female gender, and median disease duration of 1.9 years. Of the 461 patients with available radiographic data, 185 (40.1%) had erosions (score >0); their mean age was 46.7 years; 83.3% were women; and median disease duration was 1.5 years. Patients positive for HLA-DRB1 shared epitope (SE) and autoantibodies (rheumatoid factor (RF) or anti-cyclic citrullinated peptide (CCP)) had a higher risk of developing rheumatoid nodules in the presence of the AA and AG alleles of rs1801275 (odds ratio (OR)adj = 8.08 (95% confidence interval (CI): 1.60-40.89), P = 0.01 and ORadj = 2.97 (95% CI, 1.08 to 8.17), P = 0.04, respectively). Likewise, patients positive for the HLA-DRB1 SE and RF alone had a higher risk of developing rheumatoid nodules in presence of the AA and AG alleles of rs1801275 (ORadj = 8.45 (95% CI, 1.57 to 45.44), P = 0.01, and ORadj = 3.57 (95% CI, 1.18 to 10.76), P = 0.02, respectively) and in the presence of AA allele of rs1805010 (ORadj = 4.52 (95% CI, 1.20 to 17.03), P = 0.03). No significant association was found between IL4R and radiographic erosions or disease susceptibility, although our statistical power was limited by relatively small numbers of cases and controls.
We found that IL4R SNPs, rs1801275 and rs1805010, are associated with rheumatoid nodules in autoantibody-positive African-American RA patients with at least one HLA-DRB1 allele encoding the SE. These findings highlight the need for analysis of genetic factors associated with clinical RA phenotypes in different racial/ethnic populations.
PMCID: PMC2911851  PMID: 20444266
17.  Annotating the human genome with Disease Ontology 
BMC Genomics  2009;10(Suppl 1):S6.
The human genome has been extensively annotated with Gene Ontology for biological functions, but minimally computationally annotated for diseases.
We used the Unified Medical Language System (UMLS) MetaMap Transfer tool (MMTx) to discover gene-disease relationships from the GeneRIF database. We utilized a comprehensive subset of UMLS, which is disease-focused and structured as a directed acyclic graph (the Disease Ontology), to filter and interpret results from MMTx. The results were validated against the Homayouni gene collection using recall and precision measurements. We compared our results with the widely used Online Mendelian Inheritance in Man (OMIM) annotations.
The validation data set suggests a 91% recall rate and 97% precision rate of disease annotation using GeneRIF, in contrast with a 22% recall and 98% precision using OMIM. Our thesaurus-based approach allows for comparisons to be made between disease containing databases and allows for increased accuracy in disease identification through synonym matching. The much higher recall rate of our approach demonstrates that annotating human genome with Disease Ontology and GeneRIF for diseases dramatically increases the coverage of the disease annotation of human genome.
PMCID: PMC2709267  PMID: 19594883
18.  Understanding Personalized Medicine in Rheumatoid Arthritis: A Clinician's Guide to the Future 
Personalized medicine refers to the utilization of technologies at the molecular level to understand disease processes and improve health outcomes. In rheumatoid arthritis (RA) some factors associated with disease outcome have been identified. These factors have not yet been integrated into a clinically useful tool to predict disease outcome in individual patients. Developments in pharmacogenomics are moving the field forward quite rapidly. Genetic variants, which may have a role in drug metabolism mediating either drug response or toxicity, have been identified for both traditional disease modifying antirheumatic drugs and biologic agents. Choosing a medication based on a patient's characteristics (sociodemographic, clinical, genetic) will result in better utilization of resources and better clinical outcomes. The ethical, political, and legal implications of personalized medicine need to be considered as well.
PMCID: PMC3383485  PMID: 22870431
biomarkers; disease-modifying antirheumatic drugs (DMARDs); personalized medicine; pharmacogenetics; pharmacogenomics
19.  An African Ancestry-Specific Allele of CTLA4 Confers Protection against Rheumatoid Arthritis in African Americans 
PLoS Genetics  2009;5(3):e1000424.
Cytotoxic T-lymphocyte associated protein 4 (CTLA4) is a negative regulator of T-cell proliferation. Polymorphisms in CTLA4 have been inconsistently associated with susceptibility to rheumatoid arthritis (RA) in populations of European ancestry but have not been examined in African Americans. The prevalence of RA in most populations of European and Asian ancestry is ∼1.0%; RA is purportedly less common in black Africans, with little known about its prevalence in African Americans. We sought to determine if CTLA4 polymorphisms are associated with RA in African Americans. We performed a 2-stage analysis of 12 haplotype tagging single nucleotide polymorphisms (SNPs) across CTLA4 in a total of 505 African American RA patients and 712 African American controls using Illumina and TaqMan platforms. The minor allele (G) of the rs231778 SNP was 0.054 in RA patients, compared to 0.209 in controls (4.462×10−26, Fisher's exact). The presence of the G allele was associated with a substantially reduced odds ratio (OR) of having RA (AG+GG genotypes vs. AA genotype, OR 0.19, 95% CI: 0.13–0.26, p = 2.4×10−28, Fisher's exact), suggesting a protective effect. This SNP is polymorphic in the African population (minor allele frequency [MAF] 0.09 in the Yoruba population), but is very rare in other groups (MAF = 0.002 in 530 Caucasians genotyped for this study). Markers associated with RA in populations of European ancestry (rs3087243 [+60C/T] and rs231775 [+49A/G]) were not replicated in African Americans. We found no confounding of association for rs231778 after stratifying for the HLA-DRB1 shared epitope, presence of anti-cyclic citrullinated peptide antibody, or degree of admixture from the European population. An African ancestry-specific genetic variant of CTLA4 appears to be associated with protection from RA in African Americans. This finding may explain, in part, the relatively low prevalence of RA in black African populations.
Author Summary
Rheumatoid arthritis (RA) is a systemic autoimmune condition affecting the synovial membranes of diarthrodial joints. The etiology of RA is unclear but is thought to result from an environmental trigger in the context of genetic predisposition. We report that a single nucleotide polymorphism (SNP) (rs231778) in CTLA4, which encodes a negative regulator of T cell activation, is associated (p = 2.4×10−28) with protection from developing RA among African Americans. rs231778 is only polymorphic in populations of African ancestry. Protective alleles such as this one may contribute to the purported lower prevalence of RA in African Americans. Our finding appears to be independent from confounding by linkage with the HLA-DRB1 shared epitope or by genetic admixture. Furthermore, we did not replicate associations of CTLA4 SNPs with RA or other autoimmune diseases previously reported in Asians and Caucasians, such as rs3087243 (+60C/T) and rs231775 (+49A/G). The associations of different SNPs with RA susceptibility specific to different populations highlight the importance of CTLA4 in the pathogenesis of RA and demonstrate the ethnic-specific genetic background that contributes to its susceptibility.
PMCID: PMC2652071  PMID: 19300490

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