Differential Effect of Genetic Burden on Disease Phenotypes in Crohn's Disease and Ulcerative Colitis in a Canadian Cohort.

BACKGROUND AND AIMS

Crohn's disease (CD) and ulcerative colitis (UC) demonstrate considerable phenotypic heterogeneity and course. Accurate predictors of disease behaviour are lacking. The contribution of genetics and specific polymorphisms is widely appreciated; however, their cumulative effect(s) upon disease behaviour remains poorly understood. Here, we investigate the relationship between genetic burden and disease phenotype in a Canadian inflammatory bowel disease (IBD) Cohort.

METHODS

We retrospectively examined a cohort of CD and UC patients recruited from a single tertiary referral center genotyped using a Goldengate Illumina platform. A genetic risk score (GRS) incorporating strength of association (log odds ratio) and allele dose for 151 IBD-risk loci was calculated and evaluated for phenotypic associations.

RESULTS

Among CD patients, higher GRS was associated with earlier onset of disease (regression coefficient -2.19, 95% confidence interval [CI] -3.77 to -0.61, = 0.007), ileal disease (odds ratio [OR] 1.45), stricturing/penetrating disease (OR 1.72), perianal disease (OR 1.57) and bowel resection (OR 1.66). Higher GRS was associated with use of anti-tumor necrosis factor (TNF) ( < 0.05) but not immunomodulators. Interestingly, we could not demonstrate an association between higher GRS and family history of IBD (OR 1.27, = 0.07). Onset of disease remained statistically significant for never smokers ( = 0.03) but not ever smokers ( = 0.13). For UC, having a higher GRS did not predict the age of diagnosis nor was it predictive of UC disease extent ( = 0.18), the need for surgery ( = 0.74), nor medication use (immunomodulators = 0.53, anti-TNF = 0.49). We could not demonstrate an association between increased GRS and having a family history of IBD in the UC group.

CONCLUSIONS

Increasing genetic burden is associated with early age of diagnosis in CD and may be useful in predicting disease behaviour in CD but not UC.