Crohn's Disease

  • Medical Author: Adam Schoenfeld, MD
  • Medical Author: George Y. Wu, MD, PhD
  • Medical Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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Quick GuideCrohn's Disease Causes, Symptoms, Diet

Crohn's Disease Causes, Symptoms, Diet

What causes Crohn's disease?

The cause of Crohn's disease is unknown. Some scientists suspect that infection by certain bacteria, such as strains of mycobacterium, may be the cause of Crohn's disease. To date, however, there has been no convincing evidence that the disease is caused by infection per se. Crohn's disease is not contagious. Although diet may affect the symptoms in patients with Crohn's disease, it is unlikely that diet is responsible for causing the disease.

Activation of the immune system in the intestines appears to be important in IBD. The immune system is composed of immune cells and the proteins that these immune cells produce. Normally, these cells and proteins defend the body against harmful bacteria, viruses, fungi, and other foreign invaders. Activation of the immune system causes inflammation within the tissues where the activation occurs. (Inflammation is an important mechanism of defense used by the immune system.)

Normally, the immune system is activated only when the body is exposed to harmful invaders. In individuals with IBD, however, the immune system is abnormally and chronically activated in the absence of any known invader. The continued abnormal activation of the immune system results in chronic inflammation and ulceration. The susceptibility to abnormal activation of the immune system is genetically inherited. Thus, first degree relatives (brothers, sisters, children, and parents) of people with IBD are more likely to develop these diseases. Recently a gene called NOD2 has been identified as being associated with Crohn's disease. This gene is important in determining how the body responds to some bacterial products. Individuals with mutations in this gene are more susceptible to developing Crohn's disease.

Other genes are still being discovered and studied which are important in understanding the pathogenesis of Crohn's disease including autophagy related 16-like 1 gene (ATG 16L1) and IRGM, which both contribute to macrophage defects and have been identified with the Genome-Wide Association study2. In this regard, there have also been studies which show that in the intestines of individuals with Crohn's disease, there are higher levels of a certain type of bacterium, E. coli, which might play a role in the pathogenesis1. One postulated mechanism by which this could occur is though a genetically determined1 defect in elimination of the E. coli, by intestinal mucosal macrophages. The exact roles that these various factors play in the development of this disease remain unclear.

Medically Reviewed by a Doctor on 11/4/2015

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