The Genetics of Anti-Neutrophil Cytoplasmic Antibody Associated Vasculitis (AAV)
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Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a multi-systemic autoimmune disorder with evidence of circulating pathogenic ANCA. There are two main antigenic targets: proteinase 3 (PR3) and myeloperoxidase (MPO). Previous genome-wide association studies (GWAS) have provided evidence that PR3-AAV and MPO-AAV are genetically distinct autoimmune syndromes, though only three loci specific to PR3-AAV and one to MPO-AAV have been identified to date.
With the European Vasculitis Genetics Consortium, we conducted a larger GWAS, powered to discover additional risk loci in both PR3-AAV and MPO-AAV independently. A meta-analysis of two European cohorts was conducted, comprising 1,610 PR3-AAV cases, 870 MPO-AAV cases and 11,947 controls. For PTPN22 (rs6679677), a further replication cohort, previously genotyped using the Sequenom MassARRAY platform, and comprising 1,122 PR3-AAV and 347 MPO-AAV cases and 1,531 controls was included in the combined analysis.
This is the largest genome-wide association study of AAV to date and we have identified a total of 12 AAV susceptibility loci. Previously genome-wide significant loci were confirmed, including HLA class II, SERPINA1, PRTN3 and PTPN22. Seven new genome-wide significant loci were identified: three associated with PR3-AAV (BCL2L11-MIR4435-2HG, EBF3-MGMT, IGHV1-69), two with MPO-AAV (BACH2, ANKRD11-SPG7) and two shared by both (CTLA-4 and DGUOK-TET3). Further analyses based on common variants suggested that a substantial component of the genetic architecture was shared between PR3-AAV and MPO-AAV, similar to that observed between ulcerative colitis and Crohn’s disease.
In addition, Mendelian randomisation analysis confirmed that a higher eosinophil count increased the risk of PR3-AAV but not MPO-AAV, and this effect might, in part, be modulated by MIR4435-2HG through prolongation of eosinophil survival. MIR4435-2HG encodes a long non-coding RNA that plays a critical role in the regulation of BCL2L11 transcription (a Bcl2 family member essential for controlling apoptosis) in myeloid cells and hence their lifespan. We have also identified a missense variant in IGHV1-69 (rs11845244) that leads to a loss in neutralising function of antibodies generated against the NEAT2 domain of Staphylococcus aureus. This therefore provides a plausible host genetic factor in determining the susceptibility to infectious disease and as a potential driver of PR3-AAV. Overall, this study provides key novel insights into disease biology for AAV and potential therapeutic targets.
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Lyons, Paul A.