To Örebro University

Background: Perinuclear-antineutrophil cytoplasmic antibodies (P-ANCAs) have been identified in familial ulcerative colitis (UC), but the precise mechanism underlying their expression remains elusive. We assessed the role of genetic predisposition, environmental factors and systemic subclinical inflammation in the development of P-ANCA in a twin cohort with UC.

Methods: A total of 48 twin pairs (Leuven, Belgium n=4, Maastricht, The Netherlands n=6 and Örebro, Sweden n=38) with UC were included. Among these, 18 were monozygotic (3 concordant and 15 discordant for UC) and 30 were dizygotic (1 concordant and 29 discordant for UC). P-ANCA was detected through standardised ELISA, an indirect immunofluorescence assay and DNase treatment. In addition to high sensitivity C-reactive protein (hs-CRP), 92 inflammatory protein markers were measured in serum by proximity extension assay (Olink proteomics).

Results: P-ANCA was present in 16/52 (31%) of UC twins vs. 4/44 (9%) healthy twin siblings (p=0.01). No agreement in the presence of P-ANCA or their levels was observed between twin siblings in monozygotic pairs discordant for UC [intraclass correlation coefficient (ICC)=0.09] or dizygotic pairs (ICC=-0.20). Female sex was associated with an increased likelihood of P-ANCA (odds ratio, OR 5.49; 95% confidence interval, CI 1.47-20.57) and higher ANCA levels (ratio of geometric means 1.80; 95% CI 1.12-2.88). Active smoking was associated with lower concentrations of ANCA (ratio of geometric means 0.33; 95% CI 0.15-0.75) and potentially reduced the likelihood of P-ANCA (OR 0.23; 95% CI 0.02-2.21) in twins with UC but not in their healthy siblings. In twin siblings without UC, significant correlations between ANCA levels and hs-CRP, CDCP1, IL17A, CXCL9 and IL5 (correlation coefficients 0.36-0.41, p-values <0.05) were observed.

Conclusion: Female sex and tobacco smoking outweighed genetics regarding the generation and levels of P-ANCA and ANCA antibodies. The correlations between ANCA levels and inflammatory markers in healthy twin siblings suggest that P-ANCA may result from subclinical inflammation in these healthy siblings.