A SNP IN NCF4 IS ASSOCIATED WITH RF NEGATIVE RA SUPPORTING A ROLE FOR THE NOX-COMPLEX IN AUTOIMMUNITY

Background: The genetic contribution to Rheumatoid Arthritis RA is made up of multiple genes but so far few causative genes have been identified. The Ncf1 gene, encoding one of the proteins in the NADPH-oxidase (NOX) complex has been found to control arthritis in animal models by altering the capacity of the complex to produce reactive oxygen species (ROS) (1, 2). Furthermore, ROS has recently been shown to alter the redox balance on the surface of T cells, leading to increased T cell activation and arthritogenecity (3). The NOX-complex is composed of 6 proteins encoded by the genes: CYBB, CYBA, NCF2, NCF1, NCF4, RAC2. The activation of the NOX complex requires intricate interplay between the proteins of the complex and genetic alterations in any of the genes can result in altered capacity to produce ROS (4, 5).Objectives: To determine the role of ROS in RA we have investigated the association of the genes in the NOX-complex in a Swedish individually matched case-control cohort of RA patients. In humans the NCF1 gene is complicated by the presence of several duplications (6) and it is therefore difficult to investigate the association of NCF1 with RA using a SNP-based association study.Methods: We have selected and genotyped 51 SNPs from all genes of the complex excluding NCF1. Association of the SNPs with RA was investigated by analysing differences in genotype frequencies. To accurately account for sub-groups of RA patients we stratified the samples by sex, RF- and anti-CCP status. We also performed haplotype analysis of the five genes using the Haploview and WHAP softwareResults: We found that an intronic SNP, rs729749, in NCF4 is associated to arthritis in rheumatoid factor negative males (p = 0.0006). The genetic risk effect of rs729749 is homozygosity (OR = 2,44; 95% CI = 1,5 – 4,0; p = 0,0005) with a frequency of 0.80 and 0.63 in cases and controls respectively.Conclusion: This association strengthens the recent findings that ROS and the NOX-complex has an important impact on the regulation of the immune system and the development of autoimmunity.References: 1. Olofsson P, Holmberg J, Tordsson J, Lu S, Akerstrom B, Holmdahl R. Positional identification of Ncf1 as a gene that regulates arthritis severity in rats. Nat Genet 2003;33(1):25-32.2. Hultqvist M, Holmdahl R. Ncf1 (p47phox) polymorphism determines oxidative burst and the severity of arthritis in rats and mice. Cell Immunol 2005;233(2):97-101.3. Gelderman KA, Hultqvist M, Holmberg J, Olofsson P, Holmdahl R. T cell surface redox levels determine T cell reactivity and arthritis susceptibility. Proc Natl Acad Sci U S A 2006;103(34):12831-6.4. Cross AR, Noack D, Rae J, Curnutte JT, Heyworth PG. Hematologically important mutations: the autosomal recessive forms of chronic granulomatous disease (first update). Blood Cells Mol Dis 2000;26(5):561-5.5. Heyworth PG, Curnutte JT, Rae J, Noack D, Roos D, van Koppen E, et al. Hematologically important mutations: X-linked chronic granulomatous disease (second update). Blood Cells Mol Dis 2001;27(1):16-26.6. Heyworth PG, Noack D, Cross AR. Identification of a novel NCF-1 (p47-phox) pseudogene not containing the signature GT deletion: significance for A47 degrees chronic granulomatous disease carrier detection. Blood 2002;100(5):1845-51.Citation: Ann Rheum Dis, volume 66, supplement II, year 2007, page 135Session: Genomics, genetic basis of disease and HLA/T cell recognition