The phenotypic spectrum of new onset IBD in Canadian children of South Asian ethnicity: A prospective multi-centre comparative study.

INTRODUCTION Canadian-born children of South Asian (SA) ethnicity develop IBD at similar rates to Caucasian children. We evaluated the variation in phenotypic spectrum of IBD in SA and Caucasian children in a national paediatric inception cohort of new-onset IBD. METHODS Patients aged <17y enrolled in a Canadian nationwide inception cohort study were included. Baseline demographic and IBD phenotypic features were compared between SA and Caucasian children. Longitudinal outcomes through 18 months follow-up were compared matched by propensity scores. RESULTS Of 1156 children enrolled between, 2014 to 2019, 623 were Caucasian (98% and 88% parents Canadian born) and 114 SA (79% Canadian born, 87% parents SA born). Fewer SA's have a first degree relative with IBD, 6% vs 19% in Caucasians, p=0.002. SA's present at a younger age, median age 11.4y (IQR 9.2-14.3) vs 13y (IQR 10.9-15y), p=0.03 and more commonly with a UC/IBD-U subtype (ratio of UC/IBD-U to CD 1.2:1 vs 1:1.8 for Caucasians, p<0.001). Additionally, a greater proportion of SA CD patients present with colonic only disease (colonic only CD/UC/IBD-U in SAs 67% vs.57% for Caucasians, p=0.001), and among those with CD, colonic CD in SAs 31% vs 23% in Caucasians, p=0.20). Perianal fistulising disease was also numerically more common in SA (14(27%) vs.64(18%), p=0.06). Adjusting for differences in phenotypic presentation, anti-TNF exposure and time to initiation was similar, and two thirds of children, whether anti-TNF exposed or naive, were in corticosteroid-free clinical remission at 18 months irrespective of ethnicity. CONCLUSION The phenotypic spectrum of new onset IBD in SA children differs from that of Caucasian children, but treatment and clinical course are similar within phenotypic subgroups.