Rheumatoid factors in families

Use of supplementary phenotype to identify additional rheumatoid arthritis loci in a linkage analysis of 342 UK affected sibling pair families

Background

Although rheumatoid arthritis has been shown to have moderately strong genetic component, both linked loci identified in linkage analyses and susceptibility variants from association studies are short of adequately accounting for a comprehensive catalogue of the molecular factors underlying this complex disease. The objective of this study was to use supplementary phenotype based on cumulative hazard of rheumatoid arthritis to identify linkage evidence for new and additional rheumatoid arthritis loci in a genome-wide linkage analysis of 342 affected sibling pair families from the United Kingdom.

Methods

Using proportional hazards model, we estimated cumulative hazard of rheumatoid arthritis and then used it as a quantitative trait in a non-parametric multipoint variance component linkage analysis with 353 microsatellite markers distributed across the 22 autosomal chromosomes.

Results

We identified 3 new loci with genome-wide suggestive linkage evidence for rheumatoid arthritis on 9q21.13, 15p11.1 and 20q13.33. Our results also confirmed previously reported linkage evidence in the HLA-DRB1 region on chromosome 6 and on locus 1q32.1.

Conclusion

This study demonstrates the potential for information gain through the use of supplementary phenotypes in genetic study of complex diseases to identify new and additional potential linked loci that are not detected by linkage analysis of traditional phenotypes; and our results provide further evidence of the involvement of multiple loci in the genetic aetiology of rheumatoid arthritis.

Genome-wide meta-analysis for rheumatoid arthritis

Meta-analysis is being increasingly used as a tool for integrating data from different studies of complex phenotypes, because the power of any one study to identify causal loci is limited. We applied a novel meta-analytical approach (Loesgen et al. in Genet Epidemiol 21(Suppl 1):S142-S147, 2001) in compiling results from four studies of rheumatoid arthritis in Caucasians including two studies from NARAC (Jawaheer et al. in Am J Hum Genet 68:927-936, 2001; Jawaheer et al. in Arthritis Rheum 48:906-916, 2003), one study from the UK (MacKay et al. in Arthritis Rheum 46:632-639, 2001) and one from France (Cornelis et al. in Proc Natl Acad Sci USA 95:10746-10750, 1998). For each study, we obtained NPL scores by performing interval mapping (2 cM intervals) using GeneHunter2 (Kruglyak et al. in Am J Hum Genet 58:1347-1363, 1996; Markianos et al. in Am J Hum Genet 68:963-977, 2001). The marker maps differed among the three consortium groups, therefore, the marker maps were aligned after the interval mapping was completed and the NPL scores that were within 1 cM of each other were combined using the method of Loesgen et al. (Genet Epidemiol 21(Suppl 1):S142-S147, 2001) by calculating the weighted average of the NPL score. This approach avoids some problems in analysis encountered by using GeneHunter2 when some markers in the sample are not genotyped. This procedure provided marginal evidence (P<0.05) of linkage on chromosome 1, 2, 5 and 18, strong evidence (P<0.01) on chromosomes 8 and 16, and overwhelming evidence in the HLA region of chromosome 6.

Genetic dissection of a rat model for rheumatoid arthritis: significant gender influences on autosomal modifier loci

Rheumatoid arthritis (RA) is a common, chronic, autoimmune, inflammatory disease that is influenced by genetic factors including gender. Many studies suggest that the genetic risk for RA is determined by the MHC, in particular class II alleles with a 'shared epitope' (SE), and multiple non-MHC loci. Other studies indicate that RA and other autoimmune diseases, in particular insulin-dependent diabetes mellitus (IDDM) and autoimmune thyroid disease (ATD), share genetic risk factors. Rat collagen-induced arthritis (CIA) is an experimental model with many features that resemble RA. The spontaneous diabetes-resistant bio-breeding rat, BB(DR), is of interest because it is susceptible to experimentally induced CIA, IDDM and ATD, and it has an SE in its MHC class II allele. To explore the genetics of CIA, including potential gender influences and the genetic relationships between CIA and other autoimmune diseases, we conducted a genome-wide scan for CIA regulatory loci in the F(2) progeny of BB(DR) and CIA-resistant BN rats. We identified 10 quantitative trait loci (QTLs), including 5 new ones (Cia15, Cia16*, Cia17, Cia18* and Cia19 on chromosomes 9, 10, 18 and two on the X chromosome, respectively), that regulated CIA severity. We also identified four QTLs, including two new ones (Ciaa4* and Ciaa5* on chromosomes 4 and 5, respectively), that regulated autoantibody titer to rat type II collagen. Many of these loci appeared to be gender influenced, and most co-localized with several other autoimmune trait loci. Our data support the view that multiple autoimmune diseases may share genetic risk factors, and suggest that many of these loci are gender influenced.

Developments in epidemiological studies on rheumatoid arthritis

The present state of epidemiological knowledge concerning rheumatoid arthritis is summarized. The potential for further epidemiological approaches to rheumatoid arthritis is indicated and priorities listed for the future directions of such studies.

Rheumatoid factor in the United Kingdom. II. Associations with certain infections

Persons having positive tests for rheumatoid serum factors in population samples in Leigh (Lancashire) and Wensleydale (Yorkshire) were investigated for evidence of infection. Comparison was made with seronegative persons and with persons having doubtful titres matched by age and sex with the seropositive groups.

Routine cultures were made of throat swabs and mid-stream specimens of urine were also cultured. The blood serum was assayed for ASO in both populations but for salmonella and Brucella abortus antibodies only in Leigh. The latex fixation test (LFT) was tested in both samples on the follow up but initially only in Wensleydale.

There was a significant association between the results of the sheep cell agglutination test and radiological evidence of sinusitis. Salmonella or brucella antibodies were associated significantly with a positive or doubtful sheep cell agglutination test. There was no association with the presence of haemolytic streptococci in the throat. The mean ASO titre showed some relationship to the sheep cell agglutination test in Leigh but not in Wensleydale.

The latex fixation test showed no significant association with any of the infections studied but the number with positive tests was small. Higher bacterial counts were obtained in the urine of both sheep cell agglutination (SCAT) and LFT positive than in seronegative individuals but the differences were not significant.

There was no significant association between arthritis and any of the infections studied.

Of those with a positive SCAT at the final test, 41% had rheumatoid arthritis, 24% had evidence of salmonella or brucella infection, 15% had sinusitis, 3% tuberculosis and 3% influenza.

Heberden Oration, 1969. Rheumatoid arthritis--nature or nurture?

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