Date Published: April 7, 2015
Publisher: Public Library of Science
Author(s): Eric I. Benchimol, Douglas G. Manuel, Teresa To, David R. Mack, Geoffrey C. Nguyen, Jennifer L. Gommerman, Kenneth Croitoru, Nassim Mojaverian, Xuesong Wang, Pauline Quach, Astrid Guttmann, Harry Zhang.
There is a high and rising rate of immune-mediated diseases in the Western world. Immigrants from South Asia have been reported to be at higher risk upon arrival to the West. We determined the risk of immune-mediated diseases in South Asian and other immigrants to Ontario, Canada, and their Ontario-born children.
Population-based cohorts of patients with asthma, type 1 diabetes (T1DM), type 2 diabetes (T2DM), and inflammatory bowel disease (IBD) were derived from health administrative data. We determined the standardized incidence, and the adjusted risk of these diseases in immigrants from South Asia, immigrants from other regions, compared with non-immigrant residents of Ontario. The risk of these diseases in the Ontario-born children of immigrants were compared to the children of non-immigrants.
Compared to non-immigrants, adults from South Asia had higher risk of asthma (IRR 1.56, 95%CI 1.51-1.61) and T2DM (IRR 2.59, 95%CI 2.53-2.65). Adults from South Asia had lower incidence of IBD than non-immigrants (IRR 0.32, 95%CI 0.22-0.49), as did immigrants from other regions (IRR 0.29, 95%CI 0.20-0.42). Compared to non-immigrant children, the incidence of asthma (IRR 0.66, 95%CI 0.62-0.71) and IBD (IRR 0.47, 95%CI 0.33-0.67) was low amongst immigrant children from South Asia. However, the risk in Ontario-born children of South Asian immigrants relative to the children of non-immigrants was higher for asthma (IRR 1.75, 95%CI 1.69-1.81) and less attenuated for IBD (IRR 0.90, 95%CI 0.65-1.22).
Early-life environmental exposures may trigger a genetic predisposition to the development of asthma and IBD in South Asian immigrants and their Canada-born children.
Over the past century, the prevalence of immune-mediated chronic diseases has increased worldwide . Many of these disorders are of higher prevalence in Westernized nations, with low prevalence noted in people living in South Asia [2–4]. Migrant studies have been used to disentangle the role of environmental exposures from genetic risk. Higher rates of immune disorders in migrants from South Asia to the West have suggested that environmental exposures are partially related to high prevalence observed in Westernized nations [5–7]. There is a paucity of information related to the risk of immune diseases in the children of South Asian immigrants born in Western nations.
In this study, we have reported population-based estimates of incidence and prevalence of multiple immune-mediated chronic diseases in immigrants to Canada from South Asia, as well as their Canadian-born children. In so doing, we have assessed the interaction between early-life exposure to the Canadian environment and the South Asian genetic background on the risk of these disorders. Adults from South Asia had higher risk of asthma and T2DM, compared to either non-immigrants or immigrants from other regions. Adults from South Asia had lower incidence of IBD than non-immigrants, but similar rates to immigrants from other regions. Although the incidence of asthma and IBD was low amongst immigrant children from South Asia relative to non-immigrant children, rates of asthma were higher in their Ontario-born children, and the risk of IBD in Ontario-born children of South Asian immigrants was similar to the children of non-immigrants. This did not occur in the children of immigrants from other regions, who were predominantly from East Asia or the Caribbean. These findings imply a significant effect of early-life exposure to the Canadian environment on the risk of asthma and IBD, but not of T1DM for Canadian-born South-Asians.
In the largest study of South Asian migrants to date, we have demonstrated a high incidence of asthma and IBD in the Ontario-born children of South Asian immigrants relative to their immigrant parents. In addition, South Asian immigrants themselves have high rates of T2DM and asthma relative to non-immigrants. While numerous environmental risk factors have been implicated in the development of these disorders, we anticipate that this study will spur the search for gene-environment interactions. Focusing our efforts on the early-life exposures of the children of South Asian immigrants may aid in the search for specific environmental risk factors for immune-mediated disorders.