The cause of the inflammatory bowel diseases (IBD) ulcerative colitis and Crohn’s disease is not known. However, there is good 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. The purpose of this review is to highlight the important genetic aspects of IBD.
There is strong evidence to suggest a genetic basis for IBD, including familial clustering and racial and ethnic differences in risk for IBD. Ten to twenty percent of affected individuals will have 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.
Increased rates of IBD among identical twins compared to fraternal twins, and among siblings compared to spouses of affected individuals, suggests that genetic rather than environmental factors are primarily responsible for the observed familial aggregation or concentration of incidence for the disease.
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 descent. Furthermore, within Jewish populations, rates are higher in Ashkenazi than Sephardic Jews. These differences occur across different time periods and geographic areas, suggesting a genetic basis as the most likely explanation for these findings.
Recently, the first gene associated with Crohn’s disease, the NOD2 gene, was identified. There is intense ongoing research into understanding how defects in the NOD2 gene leads to Crohn’s disease and into finding the other genes that cause IBD (It is likely that there are 4-5 genes involved).
Finding causative genes will be of great importance in better understanding the underlying changes that lead to IBD. This could, in turn, be of potential great benefit in predicting the course of disease in individual patients and in guiding appropriate medical therapy. Such information also could potentially allow for identification of family members at risk for developing IBD.
© Copyright 1995-2009 The Cleveland Clinic Foundation. All rights reserved.
Can't find the health information you’re looking for?
This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 12/3/2007...#7111