The Cleveland Clinic

Digestive Diseases: Causes of Inflammatory Bowel Disease

The cause of the inflammatory bowel diseases (IBD) ulcerative colitis and Crohn's disease is not known. However, there is evidence to suggest that these diseases are due to a combination of factors, including genetic predisposition, environmental factors and alterations in the function of the immune system.

There is strong evidence to suggest a genetic basis for IBD, including:

Family history:

Ten to twenty percent of affected individuals will have a family history of IBD, with the highest risk among first-degree relatives. At this time, a positive family history is the single-greatest risk factor for IBD, with relatives of affected individuals having at least a 10-fold increased risk for IBD.

Race and ethnicity:

Racial differences in IBD incidence exist, with the highest rates among Caucasians. Also, there is evidence for ethnic aggregation of IBD, with higher rates of IBD among those of Jewish decent. Furthermore, within Jewish populations, rates are higher in Ashkenazi Jews (of European descent). These differences occur across different time periods and geographic areas, suggesting a genetic basis as the most likely explanation for these findings.

Genes Linked to IBD

Recently the first gene associated with Crohn's disease , the NOD2 gene, was identified. Ongoing research is looking into how defects in the NOD2 gene leads to Crohn's disease and finding the other genes that cause IBD (it is likely that there are 4-5 genes involved).