Background: Tumour necrosis factor alpha (TNFalpha) is a powerful inflammatory mediator in rheumatoid and other types of inflammatory arthritis. Polymorphisms within the TNFalpha gene have previously been investigated to determine their role in the aetiopathogenesis of rheumatoid arthritis ( RA), but it is unclear whether reported associations are with susceptibility to, or severity of, disease.Objective: To examine the association between both individual TNFalpha single nucleotide polymorphisms (SNPs) and haplotypes with the development and severity of erosions by 5 years in patients with inflammatory polyarthritis (IP).Methods: 438 patients from the Norfolk Arthritis Register observational inception cohort of patients with IP were x rayed 5 years after disease onset. They were genotyped for nine SNPs mapping to the TNFalpha gene, using a SNaPshot primer extension assay. Haplotypes were constructed in patients with IP, who were compared for the presence and extent of erosions at 5 years.Results: No association between individual TNFalpha SNPs or haplotypes in the patients who developed erosions at 5 years compared with those who remained non-erosive was found. Restricting analysis to patients who satisfied ACR criteria for RA by 5 years did not affect the conclusions.Conclusion: The TNFalpha gene does not seem to be associated with severity as assessed by erosive outcome at 5 years in patients with IP.

Rheumatoid arthritis (RA) is an oligogenic autoimmune disease but, to date, linkage and association to major histocompatibility complex (MHC) has been the only consistent finding in genetic studies. However, MHC is estimated to contribute only 30-40% of the total genetic component to disease susceptibility. Studies in animal models of inflammatory arthritis have identified a number of putative vulnerability loci but the homologous regions in the human genome have not previously been investigated as candidate RA susceptibility loci. We have investigated linkage to five regions homologous to those identified in animal models of inflammatory arthritis in RA affected sibling pair (ASP) families. Linkage to 17q22 syntenic to a susceptibility locus common to two experimental rat models was detected in 200 RA ASP families and replicated in a further 100 RA ASP families. Linkage to additional markers mapping to the area has refined the extent of linkage to a 4 cM region. Association to one of the markers (D17S807) was demonstrated in this cohort using extensions of the transmission disequilibrium test. Association to two 2-marker haplotypes including this marker was detected in an independent cohort of single-case RA families, thus narrowing the region harbouring the aetiological mutation to similar to1 cM. This is the first time that an arthritis susceptibility locus mapped in experimental animal models of disease has been used to identify a novel RA susceptibility locus in humans. The difficult task of identifying a disease mutation from a linkage result should, in this case at least, be facilitated by the combined use of animal and human based investigations.