Genetics of inflammatory bowel disease: from bench to bedside?

Update on the genetics of inflammatory bowel disease

There is a general consensus that interplay of genetic and environmental factors leads to an overactive mucosal immune response, which mediates the tissue damage in inflammatory bowel disease. Ethnic aggregation of inflammatory bowel disease (particularly, increased incidence and prevalence in the Ashkenazim), familial aggregation of inflammatory bowel disease, and greater concordance for inflammatory bowel disease in monozygotic twins than dizygotic twins are 3 lines of evidence for a central role of genetic factors in the pathogenesis. The genetics of inflammatory bowel disease cannot be explained by simple Mendelian genetics; it is characterized by incomplete penetrance, multiple susceptibility loci and genetic heterogeneity. Unraveling the complex genetics of inflammatory bowel disease is a daunting challenge, but the perseverance of inflammatory bowel disease gene hunters has produced commendable results in recent years. Since 1996, the field of inflammatory bowel disease genetics has progressed from publication of the first systematic genome searches for inflammatory bowel disease susceptibility loci to the identification of Crohn disease-associated genetic variants in CARD15/NOD2. Strategies for finding additional inflammatory bowel disease genes include taking advantage of the greater resolution and power of linkage disequilibrium mapping, mapping by admixture disequilibrium in African-American and Hispanic-American populations, stratifying genetic analyses by genotypes at known inflammatory bowel disease loci, and refining inflammatory bowel disease phenotypes to reduce genetic heterogeneity and simplify the search for additional inflammatory bowel disease genes.

Genetic and environmental context determines the course of colitis developing in IL-10-deficient mice

This review summarizes how interleukin-10 (IL-10)-deficient mice have permitted new insight into the complex interaction between genes and environment underlying pathogenesis of inflammatory bowel disease (IBD). The C57BL/6J strain develops only mild typhlocolitis in response to IL-10 deficiency. In contrast, C3H/HeJBir represents an unrelated inbred strain with high IBD susceptibility. Ability to identify quantitative trait loci segregating for susceptibility when the two IL-10-deficient stocks were intercrossed depended both on genome "context" (F2 versus reciprocal backcrosses) and on the physical environment. These findings are discussed in the context of recent advances in understanding the complex genetic basis for IBD in humans.