Are inflammatory bowel diseases hereditary?

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

There is strong evidence to suggest a genetic basis for IBD. Ten to 20 percent of people diagnosed with IBD also have a family history of IBD, with the highest risk among first-degree relatives (mother, father, sister, or brother). At this time, a positive family history is the single greatest risk factor for IBD. Relatives of affected individuals have at least a 10-fold increased risk for IBD.

Up to 25 percent of patients with IBD have a first-degree relative with the disease, and siblings and children of patients with IBD have a 5 percent to 10 percent risk of developing IBD in their lifetimes.

Increased rates of IBD among identical twins (compared to fraternal twins) and among siblings compared to spouses of affected individuals suggest that genetic rather than environmental factors are primarily responsible for the observed familial concentration of incidence for the disease.

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 help identify family members at risk for developing IBD.