Scientists have several theories about what causes Crohn’s disease, but they can't say for sure how someone develops the digestive condition. Most experts agree, however, that a combination of genetics and other factors play into the development of Crohn's disease. Josh Korzenik, MD, an assistant professor at Harvard Medical School and co-director of the Crohn's and Colitis Center at Massachusetts General Hospital in Boston, says Crohn’s disease is "probably caused by the interaction of genetics and intestinal bacteria."
For many years, Crohn’s was believed to be an autoimmune disorder, the result of the body’s immune system attacking its own tissues and resulting in the inflammation that is characteristic of Crohn’s disease. Now, researchers believe that it is a bit more complicated than that.
Genetics and Crohn’s Disease
Scientists’ understanding of the genetics of Crohn’s disease is expanding all the time. At this point, says Dr. Korzenik, more than 30 genes have been linked to Crohn’s disease. Some researchers think there could be as many as 100 genes involved in Crohn’s disease susceptibility.
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Another factor that could determine whether you develop Crohn’s disease is family history. The child of a parent with Crohn’s disease, says Korzenik, has a 3 to 7 percent risk of getting Crohn’s disease themselves. With identical twins, the likelihood of the other twin developing Crohn’s is around 50 percent, he says. “So there is a genetic risk factor, but it’s not so huge that the disease [can be classified as] genetically determinant.” In fact, nearly 75 percent of Crohn’s disease sufferers do not have any family members with Crohn’s.
Bacteria and Crohn’s Disease
Many kinds of bacteria are present in the intestine, where they are essential to digestion. Korzenik says the environment in the intestine may be a determining factor in whether or not a person develops Crohn’s disease. The type of bacteria living in the gut may be responsible for whether a person genetically susceptible to Crohn’s disease ultimately develops the condition.
The Immune System and Inflammation in Crohn’s Disease
Although a malfunctioning immune system may not be the root cause of Crohn’s disease, it may be a result. There are several theories about the immune system’s role in the inflammation that characterizes Crohn’s disease. Researchers think that inflammation could either be caused directly by bacteria in the intestine, or as a result of the immune system working too hard to clear out these bacteria and not knowing when to stop.
Lifestyle Factors and Crohn’s Disease
Certain lifestyle factors may also play a role in the development of Crohn’s disease, including:
- Smoking. Researchers are not yet sure why smoking affects the digestive system, but they do know that both current and former smokers are more likely to develop Crohn’s disease than nonsmokers.
- Diet. Because Crohn’s disease affects the digestive system, many people assume that diet must play a causal role in Crohn’s disease. And while it is known that some foods can trigger the symptoms of Crohn's disease, there is currently no evidence to suggest that diet can cause the disease itself. Korzenik confirms that “diet is probably important, but we don’t yet know how.”
- Stress. Stress does not cause Crohn’s disease. Many people with inflammatory bowel disease do think stress plays a part in their disease, and indeed there is a link between stress and flare-ups of Crohn’s disease symptoms. However, a recent study found no evidence to suggest that stress causes Crohn’s disease.
The Bottom Line: While the reason for your Crohn’s disease may not be known just yet, chances are that it is caused by multiple factors that are out of your control. Researchers are working on determining precisely what causes Crohn's disease so that they can continue to develop effective treatments — and the more they learn about its causes, the better those treatments will be.