Genes associated with rheumatoid arthritis and mild inflammatory arthritis. I. Major histocompatibility complex class I, II, and III allotypes

Increased frequency of the C4A*6 rare allele in rheumatic heart disease

The aim of the present investigation was to determine whether the alleles of the MHC class III complement proteins BF, C2 and C4 (C4A and C4B) could be markers for RHD in the Brazilian population. Forty-nine patients with chronic RHD were studied. The controls included 65 healthy unrelated individuals, matched with the patients according to sex, age and ethnical background. BF, C2, C4A and C4B allotypes were determined by standard technologies including Western blots for C2 and C4 variants with monoclonal and policlonal antibodies. The results showed a significantly elevated presence of the C4A*6 rare allele (p = 0.003 RR = 11.85) and a decrease of C4A*3 in the patients. In addition, C4 null and BF and C4 rare alleles were more frequent in patients than in the controls. Considering that in this investigation only RHD patients were included, further studies are necessary in order to clarify whether C4A6 is a marker for the cardiac form or for the disease itself.

Genetic typing of patients with inflammatory arthritis at presentation can be used to predict outcome

OBJECTIVE

To test the hypothesis that genetic characterization of patients at the time they present with inflammatory arthritis can predict subsequent destructive disease.

METHODS

We evaluated 177 patients with early arthritis. Patients were serologically tested for rheumatoid factor (RF) and were DNA oligotyped for the presence of conserved base sequences in the third hypervariable region (HVR3) of the DRB1 gene, previously shown to be associated with severe rheumatoid arthritis (RA). Homozygosity in the patient's genotype was confirmed using restriction fragment length polymorphism analysis. The main outcome measure was radiologic erosions at 1 year.

RESULTS

At presentation, 120 patients fulfilled the American College of Rheumatology 1987 criteria for RA, 64% of whom possessed the conserved base sequences, compared with 45% of 347 healthy controls (P < 0.001) and with 56% of 57 patients with other inflammatory arthritis (P not significant). Within the RA population, the frequency of Dw4/Dw14 compound heterozygotes was disproportionately increased. The presence of either HVR3 or RF had a relative risk of 13.49 for erosions, with a sensitivity of 95% (specificity 39%); the presence of both HVR3 and RF had a relative risk of 8.13, with a specificity of 88% (sensitivity 53%). All but 1 patient with the Dw4/Dw14 genotype developed erosions within 1 year.

CONCLUSION

Knowledge of a patient's HLA-DR type and RF status allows clinically useful prediction of erosive disease; patients possessing Dw4/Dw14 represent a particularly high-risk subgroup.

A molecular and serologic analysis of the major histocompatibility complex and complement component C4 in systemic sclerosis

OBJECTIVE

To investigate the contributions of the major histocompatibility complex (MHC) and C4 alleles to systemic sclerosis (SSc), and to pulmonary fibrosis and autoantibody expression in SSc, by analysis at the DNA level.

METHODS

One hundred fifteen patients with SSc were tested serologically for alleles of the class I MHC loci, and were tested for class II alleles (DRB, DQA, and DPB) by a combination of restriction fragment length polymorphism (RFLP) analysis and oligonucleotide probes with polymerase chain reaction amplification. C4 was studied by protein phenotyping and RFLP analysis in 80 patients. Correlations were made between disease status, pulmonary fibrosis, and expression of anticentromere antibodies (ACA) and anti-Scl-70.

RESULTS

The C4A-null phenotype was found to provide the strongest disease association factor of the MHC region (P = 0.000064, relative risk [RR] = 2.8, etiologic fraction [EF] = 32.1). The primary MHC susceptibility allele was found to be DQA2 (Pcorr = 0.0009, RR = 2.5, EF = 35.6), which is in linkage disequilibrium with both DR3 and DR11. DR2 was protective, but only for female patients (P = 0.0021, RR = 0.42, protective fraction = 19.4). DR52a was the primary MHC allele associated with pulmonary fibrosis in SSc patients. Expression of ACA was associated with the presence of either DR1 or DR4 (P = 0.0015, RR = 6.7, EF = 78.0). Anti-Scl-70 expression correlated with an acidic residue of DP beta (DPB1:69:E) (P = 0.0063, RR = 4.6, EF = 53.1).

CONCLUSION

Of all the potential markers of disease susceptibility analyzed, the C4A locus was the strongest. C4AQ0 and DQA2 are independent susceptibility factors for SSc. The development of pulmonary fibrosis in SSc patients can be predicted using combined MHC and autoantibody analysis. The MHC alleles associated with the expression of disease-specific autoantibodies are not markers for disease susceptibility.

Properdin factor B and complement factor C4 allotypes in rheumatoid arthritis: results of a follow-up study

The association between allotypes of properdin factor B (Bf), the fourth component of complement (C4A and C4B), and rheumatoid arthritis (RA), was investigated in a well-characterized cohort of RA patients who were followed from an early phase of the disease for a mean duration of 6 years. The frequencies of probable heterozygous C4AQ0 and of C4A3 were lower in RA patients compared to controls, irrespective of the presence of DR4 [relative risk (RR): 0.52 and 0.49, respectively, 95% confidence intervals (95% CI): 0.34-0.80 and 0.29-0.82]. The frequency of C4A4 was higher in RA patients compared to controls (RR: 1.86, 95% CI: 1.03-3.35), especially in DR4 positive RA patients compared to DR4 positive controls (RR: 2.58, 95% CI: 1.07-6.25), indicating a positive association of this allotype with RA additional to DR4. Bf and C4B allotypes were comparable in RA patients and controls. We did not find significant differences in Bf and C4 allotype frequencies in RA patients subdivided according to severity of the disease into a mild group and a progressive group. Because of inconsistent results in all studies on Bf and C4 allotypes, we conclude that C4 and Bf allotypes do not seem to have an important independent effect on determining disease susceptibility.

The search for laboratory measures of outcome in rheumatoid arthritis

A large number of laboratory tests have been developed within the past decade to measure factors involved in the immune inflammation of RA. These can be divided into genetic markers, general measures of inflammation, autoantibodies and tissue-specific markers. In general, it is simpler to prove the power of a certain test to measure the disease process than to predict outcome. Apart from RF positivity and CRP/ESR, few, if any, tests have proven to be of importance in independent studies from different centres. Among the promising candidates for future work are detailed analysis of the HLA-D region genes, sulphoxidation status, the autoantibody against RA33 nuclear antigen, soluble IL-2 receptor measuring lymphocyte activity, hyaluronate/hyaluronan or PIIINP from synovial tissue, the combined use of COMP and proteoglycan epitope tests for cartilage matrix, and pyrodinoline cross-linking for collagen from bone and cartilage. The ideal setting for testing such markers are prospective cohort studies starting early in the disease, and since many such studies have been initiated recently, one can expect much new information in coming years. Attention needs to be devoted to the kinetics of marker metabolism, since many are degraded or removed at very fast rates from the circulation, making serum assays less informative.

Genes associated with rheumatoid arthritis and mild inflammatory arthritis. II. Association of HLA with complement C3 and immunoglobulin Gm allotypes

Associations were sought between major histocompatibility complex (MHC) genes on chromosome 6 and the complement component C3 and immunoglobulin genes located on other chromosomes which might contribute to susceptibility to mild inflammatory arthritis (IA) or definite rheumatoid arthritis (RA). Frequencies of the complement C3F allele were raised in patients with IA but were normal in patients with RA and controls. When associations between C3F and MHC genes were sought frequencies of some MHC genes were greater in patients with C3F than in those without--for example, HLA-B8 and DR3 in patients with RA and DR2 in patients with IA. Conversely, DR4 frequency was lower in patients with IA with C3F than in those without. Thus the C3F allele may act independently or exert an epistatic effect on MHC genes to increase susceptibility or protect against disease. The frequency of the immunoglobulin heavy chain allotype Glm(2) on chromosome 14 was increased in patients with RA but only in those with the phenotype Gm1,2,3,17;21,5; no significant associations were found between MHC genes and Gm phenotypes. Further, no associations of MHC, C3F, and immunoglobulin genes were shared by patients with RA and those with IA, indicating a different genetic basis for the two clinical entities.