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The association of endoplasmic reticulum aminopeptidase 2 (ERAP2) with ankylosing spondylitis (AS) was recently described in the large International Genetics of AS Consortium Immunochip study.1 Variants in ERAP2 have also been associated with inflammatory bowel disease, psoriasis, acute anterior uveitis and birdshot chorioretinopathy.2–5 Subsequent investigation demonstrated an association of ERAP2 with AS which was present when one conditioned on one of the two independent haplotypes of ERAP1 associated with AS or when HLA-B27-negative patients were analysed separately.1 These two analyses provide analogous evidence for the association of ERAP2 with AS in HLA-B27-negative cases because of the genetic interaction between HLA-B27 and the AS-associated ERAP1 variants in AS cases. ERAP1 and ERAP2 are located on chromosome 5q15 in the opposite orientation. The locus is challenging to analyse because of the strong linkage disequilibrium (LD) across the locus and the epistasis between ERAP1 and HLA-B alleles associated with AS. We therefore sought to investigate the association of ERAP2 with AS in HLA-B27-positive patients.6 This is of clinical importance because functional studies …
Contributors PCR, MAB: conceived study; contributed patients/materials; contributed to or performed analysis. M-EC, PL, AC, DE: contributed to or performed analysis; wrote/reviewed/edited the paper. LAB, KH, SL, KBJ, S-CS, MW, MW, XZ, H-JG, GC, JN, BAL, ØF, JT, KL, LJ, YL, XW, DE, RB-V, LSG, SS, NH, JM, JLF-S, MAG-G, CL-L, PB, KG, JSHG, DDG, PR, WPM, HX, IEvdH-B, C-TC, RV-O, CR-S, IMH, FMP-S, RDI, JM, MB, JDR, T-HK, BPW: contributed patients/materials; wrote/reviewed/edited the paper.
Funding PR is funded by the RACP-ARA-Starr Research Fellowship. MAB is a National Health and Medical Research Council Senior Principle Research Fellow. This work was in part funded by grants from Arthritis Research UK (19536 & 18797), the NIHR Oxford Comprehensive Biomedical Research Centre (immunity and inflammation theme A93081), NIHR Thames Valley collaborative research network and National Ankylosing Spondylitis Society (UK) and NIH/NIAMS—P01-AR052915.
Competing interests None declared.
Ethics approval UQ Human Ethics and Metro South Ethics Committee.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The data that the study uses have been fully detailed elsewhere.1
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