Genomewide search in Canadian families with inflammatory bowel disease reveals two novel susceptibility loci

The chronic inflammatory bowel diseases (IBDs)-Crohn disease (CD) and ulcer ative colitis (UC)-are idiopathic, inflammatory disorders of the gastrointe stinal tract. These conditions have a peak incidence in early adulthood and a combined prevalence of similar to 100-200/100,000. Although the etiology of IBD is multifactorial, a significant genetic contribution to disease su sceptibility is implied by epidemiological data revealing a sibling risk of similar to 35-fold for CD and similar to 15-fold for UC. To elucidate the genetic basis for these disorders, we undertook a genomewide scan in 158 Ca nadian sib-pair families and identified three regions of suggestive linkage (Sp, 5q31-33, and Gp) and one region of significant linkage to 19p13 (LOD score 4.6). Higher-density mapping in the 5q31-q33 region revealed a locus of genomewide significance (LOD score 3.9) that contributes to CD susceptib ility in families with early-onset disease. Both of these genomic regions c ontain numerous genes that are important to the immune and inflammatory sys tems and that provide good targets for future candidate-gene studies.