Do the HLA-DQ and DP genes play a role in rheumatoid arthritis?

On the association between rheumatoid arthritis and classical HLA class I and class II alleles predicted from single-nucleotide polymorphism data

Using single-nucleotide polymorphisms (SNPs), we sought to predict classical class I and class II human leukocyte antigen (HLA) alleles, and test for their associations with rheumatoid arthritis (RA) in the North American Rheumatoid Arthritis Consortium sample of cases and controls, genotyped on the Illumina HumanHap550 BeadChip. We use publicly available databases of SNP data and HLA data to find SNPs or SNP-haplotypes to be used as surrogates for each HLA allele. To reduce the confounding effects of linkage disequilibrium with the HLA-DRB1 locus, we tested for the association conditional on the presence or absence of a shared epitope allele on the same haplotype as the target HLA allele. Using SNP surrogates, we find that components of the DQ8 serotype (DQA1*0301:DQB1*0302) are associated with RA, irrespective of the presence or absence of a shared epitope allele on their respective haplotypes. Knowledge of the haplotype structure in the HLA region is still necessary for better interpretation of the results.

Blood cell gene expression profiling in rheumatoid arthritis

To study the pathogenic importance of the rheumatoid factor (RF) in rheumatoid arthritis (RA) and to identify genes differentially expressed in patients and healthy individuals, total RNA was isolated from peripheral blood mononuclear cells (PBMC) from eight RF-positive and six RF-negative RA patients, and seven healthy controls. Gene expression of about 10,000 genes were examined using oligonucleotide-based DNA chip microarrays. The analyses showed no significant differences in PBMC expression patterns from RF-positive and RF-negative patients. However, comparisons of gene expression patterns from all fourteen RA patients and healthy controls identified a subset of discriminative genes. These results were validated by real time reverse transcription polymerase chain reaction (RT-PCR) on another group of RA patients and healthy controls. This confirmed that the following genes had a significantly higher expression in RA patients than in healthy controls: CD14 antigen, defensin alpha-1 and alpha-3 (DEFA), fatty-acid-Coenzyme A ligase, long-chain 2 (FACL), ribonuclease 2 (RNASE2), S100 calcium-binding protein A8 and A12 (S100A8 and S100A12). In contrast, the expression of MHC class II, DQ beta1 (HLA-DQB1) was significantly reduced in RA patients compared to healthy controls.

CONCLUSIONS

With the analytical procedure employed, we did not find any indication that RF-positive and RF-negative RA are two fundamentally different diseases. Most of the genes discriminative between RA patients and healthy individuals are known to be involved in immunoinflammatory responses, especially those related to altered phagocytic functions.

Impact of shared epitope genotype and ethnicity on erosive disease: a meta-analysis of 3,240 rheumatoid arthritis patients

OBJECTIVE

The strongest known genetic association in rheumatoid arthritis (RA) is with HLA-DRB1 alleles that share a similar amino acid sequence, termed the shared epitope (SE). Although many studies have examined the association of the SE with disease severity, the results have been inconsistent, which may reflect the relatively small sample sizes or ethnic differences. The aim of this study was to assess the association of HLA-DRB1 SE alleles and genotype with the development of bony erosions in RA by meta-analysis.

METHODS

We identified English-language articles published between January 1, 1987 and June 1, 1999 through Medline, EMBase, and manual searches of 6 relevant journals. Included were studies in which molecular typing of HLA-DRB1 alleles was performed and in which the presence or absence of bony erosions was reported. Data were extracted from the studies, and erosions were coded as present or absent. Authors were contacted for missing information and data on individual patients.

RESULTS

A total of 29 studies and 3,240 patients were available for analysis. The summary odds ratios (ORs), when all patients were evaluated as a single group, demonstrated a significant association of the presence of the SE (2 or 1 versus 0 SE alleles) with erosions (OR 2.0; 95% confidence interval [95% CI] 1.8-2.2), although significant heterogeneity was present (P = 0.002). Subgroup analyses demonstrated the important influence of ethnic background. For example, no association of the SE with erosions was demonstrated in Greeks (OR 0.8 [95% CI 0.2-1.5]). In contrast, there was a striking dose-dependent relationship in southern European Caucasians and Asians, with ORs as high as 6.2 and 5.4, respectively, in patients with 2 SE alleles. Although our ability to assess the relationship between SE genotype and erosions was limited, particular importance of the DRB1*0401 SE allele was suggested in an analysis restricted to northern European Caucasians.

CONCLUSION

The SE is associated with the development of erosive disease in many ethnic groups; however, striking exceptions exist. These variations may be due to allele differences between populations, such as the frequency of DRB1*0401 among different ethnic groups. Further study to better understand the genetic and environmental differences between these populations may provide insight into mechanisms that influence the clinical expression of RA.