Interleukin 1 polymorphisms in patients with ankylosing spondylitis in Korea

OBJECTIVE

Studies in ankylosing spondylitis (AS) and psoriatic arthritis (PsA) cohorts have demonstrated that the interleukin 1 (IL-1) gene cluster contains a major susceptibility locus for AS and PsA. We examined the association between the IL-1 gene cluster and susceptibility to AS in Korea.

METHODS

In total, 451 patients with AS and 402 ethnically matched healthy controls were genotyped with 51 single-nucleotide polymorphisms (SNP) within the IL-1 gene cluster (specifically located within the IL1A, IL1B, IL1RN, and IL1F5-10 genes based on findings of previous association studies). Samples were genotyped by MALDI-TOF mass spectrometry using standard Sequenom iPLEX conditions. Genotyping assays were designed using AssayDESIGNER 2.0 and all SNP designed as 4 multiplex reactions. The resulting product was analyzed using the MassArray Compact Analyzer, and genotype results were determined. Univariate SNP marker distributions in case-control populations were tested by chi-square tests.

RESULTS

No SNP showed association with p value < 0.05. Haplotype analysis revealed an association with the 6 markers (empirical p < or = 2 x 10(-4), corresponding to Bonferroni corrected p = 0.05). Analysis of each 2, 3, 4, 5-marker sliding window revealed association with the IL1A locus (especially haplotype rs12622683-rs11123148-rs10165537).

CONCLUSION

Single SNP associations noted in outbred Caucasian populations were not found in the Korean AS cohort. Haplotype analysis revealed associations with IL1 locus. These results support the notion that the IL1 locus is associated with susceptibility to AS.

Genetics of psoriasis and psoriatic arthritis: update and future direction

Psoriasis and psoriatic arthritis (PsA) both have substantive genetic determinants. Numerous candidate regions and genes have now been replicated in disease susceptibility, and to a lesser extent in disease expression, in both disease entities. Intensive efforts are now under way or are being planned to perform genome-wide association scans (GWAS) in psoriasis and PsA. A major determinant of success for GWAS is likely to be accumulation of multiple large well-phenotyped cohorts, sophisticated data management, and verification of the findings. At the 2007 Annual Meeting of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA), members of the GRAPPA genetics committee presented a discussion of the genetics of psoriasis and PsA, including future trends. This article is a summary of that presentation and a review of the literature.

Clinical and genetic registries in psoriatic disease

Clinical and genetic registries are an important tool in studying psoriasis and psoriatic arthritis (PsA). They assist in delineating disease features and are crucial in defining phenotype and identifying genetic and other markers of disease expression. At the 2007 Annual Meeting of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA), members of the clinical registries and genetics committees described several ongoing registries, including their construction, protocols, and some results from their analyses. In breakout groups, members discussed data issues, including identification of core datasets, ownership, and how to share data; and ethical issues and possible sources of funding for registries. Proceedings of these meetings are summarized.

Familial aggregation of psoriatic arthritis

Objectives:

The aim of this study was to determine the recurrence risk of psoriatic arthritis (PsA) and uncomplicated psoriasis in first-degree relatives (FDRs) of patients with PsA.

Methods:

All available FDRs (full siblings, parents and children) of 100 consecutive consenting patients attending a PsA clinic were evaluated for the presence of psoriasis and PsA using a standard protocol. The protocol included a screening questionnaire, physical examination by a rheumatologist, and radiographic and laboratory assessment. The prevalence of PsA and psoriasis in FDRs of the index cases was determined, and the recurrence risk ratio (λ) was calculated, assuming a population prevalence of PsA of 0.25%, and a population prevalence of psoriasis of 2%.

Results:

The 100 probands had 533 relatives. Eighty-four of them were deceased and 53 were unavailable (age <16 years). Of the remaining 396 FDRs, 107 did not participate (living too far away/did not consent). Thus, 289/396 (73%) of the available FDRs participated in the study. There were 130 siblings, 108 parents and 51 children. The prevalence of PsA and psoriasis among FDRs was 7.6% and 15.2%, respectively. The λ1 was 30.4 for PsA and 7.6 for psoriasis. The prevalence of PsA and psoriasis in siblings was 7.7% and 17.7%, respectively. The λS was 30.8 for PsA and 8.8 for psoriasis.

Conclusions:

The recurrence risk ratio for both PsA and psoriasis is high in FDRs and siblings of patients with PsA. These results confirm that both PsA and psoriasis have a strong heritable component.

Association of interleukin-23 receptor variants with ankylosing spondylitis

OBJECTIVE

Recent studies have shown that a nonsynonymous single-nucleotide polymorphism (SNP) (Arg381Gln; rs11209026) in the interleukin-23 receptor (IL-23R) gene on chromosome 1p31 is associated with Crohn's disease and psoriasis. Given the clinical and immunologic overlap between ankylosing spondylitis (AS) and these diseases, and the potential function of this candidate SNP, this study was undertaken to examine the association of IL-23R variants with AS in multiple Canadian populations.

METHODS

We examined 3 cohorts of AS patients from established rheumatic disease centers in Canada. The majority of AS patients were Caucasians of northern European descent, and all patients satisfied the modified New York classification criteria for AS or for juvenile spondylarthritis. We examined 424 AS probands and 401 controls from Alberta, 251 AS probands and 122 controls from Toronto, and 121 AS probands and 219 controls from Newfoundland. Ten IL-23R SNPs were genotyped, 9 of which were incorporated in the haplotype analysis. Allele and haplotype associations were calculated using the WHAP software package. P values for haplotype associations were calculated using a permutation test.

RESULTS

The primary SNP of interest in a previous study of inflammatory bowel disease (IBD) (Arg381Gln; rs11209026) was found to be protective against AS in the Newfoundland population (P=0.04) and in the Toronto population (P=0.04) in single-marker univariate analysis. The strongest association, however, was with SNP rs11465804 (P=0.007 for the Newfoundland population and P=0.0007 for the Toronto population). A 3-marker sliding window omnibus test revealed a significant association with markers rs10489629, rs2201841, and rs11465804 in both the Newfoundland population (P=0.04) and the Alberta population (P=0.034). Our results were independent of the IBD and psoriasis status of the AS patients.

CONCLUSION

This concurrent analysis of 3 distinct AS populations and their regional controls demonstrates a disease association with the IL-23R locus and implicates the same polymorphisms associated with IBD and psoriasis.

The apolipoprotein E2 isoform is associated with accelerated onset of coronary artery disease in systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is a highly prevalent autoimmune disease and coronary artery disease (CAD) is a complication of SLE which is often crucial for the patient's prognosis. It is hypothesized that apolipoprotein E (Apo E), which is involved in cholesterol metabolism, might play a role in this process.

MATERIAL/METHODS

Patients with SLE registered at the University of Toronto Lupus Clinic who had DNA available for study had their Apo E genotype determined. Each case was assessed for the presence of CAD, and Apo E allele frequencies in patients with SLE were compared with data from the general population. Age at onset and disease duration of CAD were also recorded and compared between groups.

RESULTS

DNA was stored from 152 patients, of whom 38 (25%) had CAD. There was no difference in the frequencies of the Apo E isoforms between SLE patients and the general population. Patients with the E2 allele developed CAD after a mean +/-SD of 6.0+/-1.9 yrs compared with 14.5+/-5.4 yrs in those with E3/3 (p<0.01).

CONCLUSIONS

The distribution of Apo E genotypes in SLE is not significantly different from that of the North American population. In SLE, Apo E2 was associated with a more rapid development of CAD. Therefore, Apo E2 might interact with other disease-related factors to accelerate the onset of CAD in some patients with SLE and as such might be an additional marker of risk in this population.

Psoriatic arthritis: genetic susceptibility and pharmacogenetics

Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis. The etiology of PsA is unknown; however, there is mounting evidence for a strong genetic contribution to PsA. A few disease-related genes have already been identified in PsA. Cytokines associated with PsA appear to be the most promising targets for pharmacogenetics. Blockade of TNF-α and IL-12/23 is associated with a marked clinical response to PsA and/or psoriasis, implying a pivotal role of these cytokines in the pathogenesis of these two disease entities. To date, only the -308 variant of the TNF-α promoter gene has been shown to be important in predicting response to TNF-α blockade in inflammatory arthritis.

Genetic epidemiology of complex phenotypes

Genetic factors play a substantive role in the susceptibility to common diseases. Due to recent advancements in the characterization of genetic variants and large-scale genotyping platforms, multiple genes have now been identified for common, complex diseases. As a result, there is an immense interest in elucidating genetic factors in complex traits. Therefore, it is important to understand the design as well as the technical and statistical issues of the two most common approaches for gene identification: linkage and association.

The Canadian Rheumatology Association/ Spondyloarthritis Research Consortium of Canada treatment recommendations for the management of spondyloarthritis: a national multidisciplinary stakeholder project

OBJECTIVE

Development of treatment recommendations for arthritis has traditionally relied on the compilation of evidence-based data by experts in the field despite recommendations by various bodies for broad stakeholder input. Our objectives were: (1) To develop evidence-based treatment recommendations for the management of spondyloarthritis (SpA) in Canada that also incorporate the perspective of multiple stakeholders. (2) To generate a procedural template for the multidisciplinary development of treatment recommendations.

METHODS

The process was directed by a steering committee comprising the SPARCC Executive, rheumatologists from academic and community-based practice, patient consumers, and a representative from the John Dossetor Health Ethics Centre. Guidelines established by EULAR and stipulated in the AGREE instrument were followed. First, a working document was drafted that included a referenced summary of the evidence-based data and the 12 national arthritis care standards developed by the Alliance for the Canadian Arthritis Program. Second, a Web-based survey was conducted among patient consumers to address the relevance to patients of 2 primary outcome instruments that assess the effectiveness of treatment. Third, a list of questions was generated for drafting propositions by the ethics consultant. A Delphi consensus exercise was then conducted.

RESULTS

Consensus was generated on a final list of 38 treatment recommendations categorized under the subject headings of general management principles, ethical considerations, target groups, definition of target disease, disease monitoring, and specific management recommendations.

CONCLUSION

Using broad stakeholder input, we provide treatment recommendations to guide clinical practice and access to care for patients with SpA in Canada.

Genetics of ankylosing spondylitis: An update

Substantive evidence exists that genetic factors play a pivotal role in susceptibility to ankylosing spondylitis (AS). HLA-B27 remains the most convincing and universal association of a genetic factor with AS. Over the last decade there has been immense interest in elucidating genetic variants outside the major histocompatibility complex region. Due to larger AS datasets along with recent advancements in the characterization of genetic markers and large-scale genotyping platforms, replicated non-major histocompatibility candidates have now emerged. This article reviews the current evidence regarding the genetics of AS, with an emphasis on the recent major advances, and it discusses the challenges and limitations in interpreting these studies.

International spondyloarthritis interobserver reliability exercise--the INSPIRE study: I. Assessment of spinal measures

OBJECTIVE

To determine whether the axial measures used in primary ankylosing spondylitis (AS) were reproducible for both AS and psoriatic arthritis (PsA) with axial disease.

METHODS

A group of 20 rheumatologists from 11 countries with expertise in spondyloarthritis (SpA) met for a combined physical examination exercise to assess 10 patients with PsA with axial involvement (9 men, 1 woman, mean age 52 yrs, mean disease duration 17 yrs) and 9 AS patients (7 men, 2 women, mean age 38 yrs, mean disease duration 16 yrs). A modified Latin-square design was used. Measures included were occiput to wall, tragus to wall, cervical rotation, chest expansion, lateral spinal bending, modified Schober, and hip mobility. Data were analyzed using intraclass correlation coefficients (ICC) adjusted for order of measurements.

RESULTS

The majority of the variance was contributed by the patients. There was no order effect. Observer effect was noted especially for chest expansion for both AS and PsA patients, and for the modified Schober in PsA. The ICC demonstrated very good to excellent agreement for most measures for both AS and PsA. Chest expansion provided only moderate agreement for AS and PsA.

CONCLUSION

Overall, measures of spinal mobility used in primary AS perform well with respect to interobserver reliability, and are equally reproducible when applied to PsA patients with axial involvement. Thus, these measures should now be evaluated in therapeutic trials of patients with PsA to determine sensitivity to change and concordance with other measures of structural damage.

International spondyloarthritis interobserver reliability exercise--the INSPIRE study: II. Assessment of peripheral joints, enthesitis, and dactylitis

OBJECTIVE

To determine whether the assessments of peripheral joints and enthesitis were reproducible for both AS and PsA with axial disease, and whether dactylitis assessment is reproducible in patients with PsA.

METHODS

A group of 20 rheumatologists from 11 countries with expertise in spondyloarthritis (SpA) met for a combined physical examination exercise to assess 10 patients with PsA with axial involvement (9 men, 1 woman, mean age 52 yrs, disease duration 17 yrs) and 9 patients with AS (7 men, 2 women, mean age 38 yrs, disease duration 16 yrs). A modified Latin-square design that enabled assessment of patient, assessor, and order effect was used. Measures included were number of tender and swollen joints, presence of enthesitis using 6 different indices, and dactylitis score. Data were analyzed using intraclass correlation (ICC) adjusted for order of measurements.

RESULTS

The majority of the variance was contributed by the patients. There was no order effect. The assessment of tender joints (ICC 0.69) was more reliable than the assessment of swollen joints (ICC 0.54). Moreover, there was better agreement in patients with PsA (ICC 0.78) than in patients with AS (ICC 0.62). There was excellent agreement on the number of active enthesitis sites (ICC 0.86). All the enthesitis indices provided substantial to excellent agreement among observers. Agreement for the dactylitis score was substantial (ICC 0.70).

CONCLUSION

The assessment of peripheral joints is more reliable in patients with PsA. Enthesitis instruments can be used reliably in patients with AS and patients with PsA with spinal involvement. The Leeds dactylitis instrument functions well in PsA.

Association of toll-like receptor 4 variants and ankylosing spondylitis: a case-control study

OBJECTIVE

Functional single nucleotide polymorphisms within the ectoplasmic domain of the Toll-like receptor 4 (TLR4) gene have been shown to result in an endotoxin-hyporesponsive phenotype and aberrant signal transduction for bacterial agonists. TLR4 is in proximity to a genome-wide linkage peak in 9q32-33. Given the proposed function and location of TLR4, we examined the association of 2 functional variants of TLR4 in patients with ankylosing spondylitis (AS) in Newfoundland.

METHODS

In total, 101 AS patients and 100 ethnically matched controls were genotyped, using the Sequenom MassArray platform, for 2 functional variants in the TLR4 gene: Asp299Gly (A/G polymorphism) and Thr399Ile (C/T polymorphism).

RESULTS

The minor allele frequency for the Asp299Gly variant (G) was significantly higher in AS cases compared to controls (7.5% vs 2.6%, respectively; OR 3.10, p = 0.037). The minor allele frequency for the Thr399Ile variant (T) for cases and controls was 7.4% vs 3.0% (OR 2.59, p = 0.071). Haplotype analysis using Haploview noted a higher proportion of GT in the cases (for GT, chi-squared p = 0.023).

CONCLUSION

Given the functional role of TLR4 variants in the innate immune system, larger studies are now warranted to elucidate the association of TLR4 variants in AS.

Progressive and Concordant Expression of PKC-η and iNOS Phenotypes in Monocytes From Patients With Rheumatoid Arthritis: Association With Disease Severity

Rheumatoid arthritis (RA) is a relatively common autoimmune disease with strong genetic and environmental determinants. The disease manifests itself as inflammation of the synovia and usually progresses to joint erosion and destruction. The disease can also be considered as a systemic disease because extra-articular manifestations are often observed throughout many organs and tissues of the body. Patients with severe RA have altered peripheral blood monocytes (PBM) that express activation markers. Two such markers, PKC-η and iNOS, were studied using confocal laser scanning microscopy to determine how these markers are expressed during disease progression. Healthy individuals expressed neither of the two markers, but there was an elevated level of PKC-η observed as the disease progressed (40% in mild RA and 100% in severe RA patients). Concordant expression of the two markers was observed in only 3% of PBM from mild RA patients, reaching 38% in severe RA patients. No cells expressing iNOS alone were observed in any of the patients studied. These data support the hypothesis linking PKC-η expression with the regulation and predisposition to the development of the iNOS phenotype in severe RA patients. PKC-η may therefore be a key regulator in the production of elevated plasma nitric oxide (NO) and corresponding circulating reactive nitrogen intermediates in severe RA and may be a possible target to regulate iNOS induction and NO production by monocytic cells in RA patients and possibly other inflammatory diseases.

Association between the interleukin-1 family gene cluster and psoriatic arthritis

OBJECTIVE

The interleukin-1 (IL-1) cytokine elicits a wide variety of biologic activities that initiate and promote an inflammatory response. The loci in the IL1 gene cluster have recently been associated with ankylosing spondylitis (AS). Since there is clinical and immunologic overlap between psoriatic arthritis (PsA) and AS, we wanted to examine the association between a panel of single-nucleotide polymorphisms (SNPs) in the IL1 gene family cluster and chromosome 2q12-13 in a PsA cohort.

METHODS

Two hundred twelve PsA patients and 150 ethnically matched controls were genotyped with 11 SNPs in IL1A, 9 SNPs in IL1B, and 9 SNPs in IL1F5-10. Univariate analyses of the 29 single markers and short intragenic haplotypes identified several associated regions. Seventeen markers of interest were noted and further investigated to determine which markers or short haplotypes independently predict case-control status, using a stepwise logistic model. RESULTS; Two regions contributing independently to risk of disease in PsA were noted: a region spanned by markers rs3783547, rs3783543, and rs17561 in IL1A, and a region near the end of IL1B, through IL1F7, IL1F8, and into IL1F10. The best model contained markers rs3811047, rs1562304, and rs3811058, and 1 haplotype constructed from the 3 markers in region 1, with a likelihood ratio of 25.34 (4 degrees of freedom).

CONCLUSION

The IL1 locus appears to be a high-priority susceptibility locus in PsA, with at least 2 independent regions that confer increased risk.

PPAR-gamma gene polymorphisms and psoriatic arthritis

OBJECTIVE

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) activation has been shown to play a role in suppressing angiogenesis and inflammation, both important pathological features of psoriatic arthritis (PsA). Given the potential physiological role for PPAR-gamma in PsA, we examined known coding polymorphisms in the PPAR-gamma gene in a Caucasian population.

METHODS

PsA was diagnosed as an inflammatory arthritis in patients with psoriasis, in the absence of other etiologies for inflammatory arthritis. Control subjects were ascertained from the same population and were all Caucasian. DNA samples were genotyped for 4 PPAR-gamma variants by time-of-flight mass spectrometry using the Sequenom platform. All 4 single-nucleotide polymorphisms (SNP) were previously-reported coding variations, 3 of which caused an amino acid change: Pro12Ala (rs1801282), Pro40Ala (rs1805192), and Pro115Gln (rs1800571); the fourth SNP, C161T (rs3856806), was synonymous. All primers were designed using Sequenom SpectroDesigner software, and scanned using a mass spectrometry workstation.

RESULTS

Of the 4 SNP examined, Pro40Ala and Pro115Gln were found to be nonpolymorphic in our population. Minor allele frequency for patients with PsA and controls for Pro12Ala (G) were 9.0% vs 13.8% (p = 0.017) and for C161T (T) 10.7% vs 12.0% (p = 0.56), respectively. All genotypes satisfied Hardy-Weinberg equilibrium.

CONCLUSION

An association between PsA and a known coding SNP of the PPAR-gamma gene was observed in our Caucasian population. Further studies are now warranted for validation of our findings in an independent cohort.

Association of the IL1 gene cluster with susceptibility to ankylosing spondylitis: an analysis of three Canadian populations

OBJECTIVE

To examine the association between the IL1 gene cluster and susceptibility to ankylosing spondylitis (AS) in 3 independent case-control cohorts.

METHODS

We analyzed 394 patients and 446 controls from Alberta, Newfoundland, and Toronto, Canada. Samples were genotyped using a panel of 38 single-nucleotide polymorphism (SNP) markers within the IL1 gene cluster. Data from 20 informative and nonredundant SNP markers were analyzed using several association test strategies. First, we used the program WHAP to identify single-marker associations. Second, we used WHAP to analyze "sliding windows" of 3 contiguous markers along the entire extent of the IL1 gene cluster in order to identify haplotypic associations. Third, we used the linkage disequilibrium mapping program DMLE to estimate the posterior probability distribution of a disease locus.

RESULTS

A total of 14 SNP markers showed significant single-locus disease associations, the most significant being rs3783526 (IL1A) (P = 0.0009 in the Alberta cohort, P = 0.04 in the Newfoundland cohort) and rs1143627 (IL1B) (P = 0.0005 in the Alberta cohort, P = 0.02 in the Newfoundland cohort). Analysis of 3-marker sliding windows revealed significant and consistent associations with all of the haplotypes in the IL1A and IL1B loci in the Alberta cohort and with IL1B in the Newfoundland cohort, especially haplotypes rs1143634/rs1143630/rs3917356 and rs1143630/rs3917356/rs3917354 (P = 0.006-0.0001). With DMLE, a strong peak in the probability distribution was estimated near IL1A in both the Alberta and the Newfoundland populations.

CONCLUSION

These results indicate that the IL1 locus, or a locus close to IL1, is associated with susceptibility to AS.

Magnitude and distribution of linkage disequilibrium in population isolates and implications for genome-wide association studies

The genome-wide distribution of linkage disequilibrium (LD) determines the strategy for selecting markers for association studies, but it varies between populations. We assayed LD in large samples (200 individuals) from each of 11 well-described population isolates and an outbred European-derived sample, using SNP markers spaced across chromosome 22. Most isolates show substantially higher levels of LD than the outbred sample and many fewer regions of very low LD (termed 'holes'). Young isolates known to have had relatively few founders show particularly extensive LD with very few holes; these populations offer substantial advantages for genome-wide association mapping.

Association of functional variants of PTPN22 and tp53 in psoriatic arthritis: a case-control study

Recent studies have implicated PTPN22 and tp53 in susceptibility to several autoimmune diseases, including rheumatoid arthritis, suggesting that these genes are important in maintaining immune homeostasis. Because autoimmune diseases may share similar susceptibility loci, investigation of these genes in psoriatic arthritis (PsA) is of potential relevance. As a result we investigated known coding polymorphisms in PTPN22 and tp53 in a homogenous Caucasian PsA cohort from Newfoundland, Canada and an admixed Caucasian PsA cohort from Toronto, Canada. We observed a moderate association of the R620W variant of PTPN22 with PsA in the Toronto population only. Because of the conflicting findings reported regarding the association of PTPN22 with PsA, further studies in other PsA populations are warranted.

Association between a variation inLRCH1 and knee osteoarthritis: A genome-wide single-nucleotide polymorphism association study using DNA pooling

OBJECTIVE

To perform a large-scale association analysis of single-nucleotide polymorphisms (SNPs) in patients with radiographically defined osteoarthritis (OA) of the knee.

METHODS

We examined >25,000 SNPs located within approximately 14,000 genes for associations with radiographically defined knee OA, using polymerase chain reaction and MassExtend amplification techniques. Allele frequencies were estimated initially in DNA pools from 335 female patients with knee OA and 335 asymptomatic and radiographically negative female control subjects. All were of northern European ancestry. Significant allele frequency differences were validated by genotyping of individual DNA samples. Confirmed significant findings were verified in 2 additional case-control samples from the UK (443 cases and 303 controls) and Newfoundland (346 cases and 264 controls). Chondrosarcoma cell lines were used to test for potential differences in gene expression.

RESULTS

The marker most strongly associated with the risk of knee OA was rs912428, a C/T polymorphism in intron 1 of LRCH1, a gene on chromosome 13q14 that encodes a novel protein of as-yet-unknown function. The frequency of the T allele compared with controls was consistently increased by 40% across all 3 case-control groups. Additional subanalyses in case-control samples with hip OA and hand OA suggested similar trends, but did not reach statistical significance. Association fine-mapping using 10 additional SNPs in LRCH1 confirmed intron 1 as the region of highest association but failed to reveal variations with significance stronger than the marker SNP, as did the haplotype analysis. LRCH1 was not up-regulated or overexpressed in chondrosarcoma cell lines exposed to inflammatory stimuli, suggesting a possible structural role.

CONCLUSION

A genetic variant in LRCH1 was consistently associated with knee OA in 3 samples from 2 populations. Our results also suggest that the same association with OA may exist at other sites. Additional genetic and experimental work is needed to elucidate the precise mechanism by which the LRCH1 gene influences OA risk.

TNFalpha polymorphisms and risk of psoriatic arthritis

BACKGROUND

Tumour necrosis factor alpha (TNFalpha) is a cytokine of critical importance in psoriatic arthritis.

OBJECTIVES

(1) To examine the association between TNFalpha promoter gene polymorphisms and psoriatic arthritis in two well characterised Canadian populations with the disease; (2) to carry out a meta-analysis of all TNFalpha association studies in white psoriatic arthritis populations.

METHODS

DNA samples were genotyped for five TNF variants by time of flight mass spectrometry using the Sequenom platform. All five single nucleotide polymorphisms were in the 5' flanking region of TNFalpha gene at the following positions: -1031 (T-->C), -863 (C-->A), -857 (C-->T), -308 (G-->A), and -238 (G-->A). Primary analyses were based on logistic regression. Summary estimates of disease/genotype relations from several studies were derived from random effects meta-analyses.

RESULTS

237 psoriatic arthritis subjects and 103 controls from Newfoundland and 203 psoriatic arthritis subjects and 101 controls from Toronto were studied. A combined analysis of data from both populations, showed a significant association between disease status and the -238(A) variant (p=0.01). The meta-analysis estimate for the -238(A) TNFalpha variant in eight psoriatic arthritis populations was also significant (odds ratio=2.29 (95% confidence interval, 1.48 to 3.55)).

CONCLUSIONS

Analysis of TNFalpha variants in psoriatic arthritis populations shows that the -238 (A) variant is a significant risk factor for this disease.