What is Crohn"s disease?
Crohn"s disease is a chronic inflammatory disease of the intestines. It primarily causes ulcerations (breaks in the lining) of the small and large intestines, but can affect the digestive system anywhere from the mouth to the anus. It is named after the physician who described the disease in 1932. It also is called granulomatous enteritis or colitis, regional enteritis, ileitis, or terminal ileitis.
Crohn"s disease is related closely to another chronic inflammatory condition that involves only the colon called ulcerative colitis. Together, Crohn"s disease and ulcerative colitis are frequently referred to as inflammatory bowel disease (IBD). Ulcerative colitis and Crohn"s disease have no medical cure. Once the diseases begin, they tend to fluctuate between periods of inactivity (remission) and activity (relapse). They affect approximately 500,000 to two million people in the United States. Men and women are equally affected. IBD most commonly begins during adolescence and early adulthood, but it also can begin during childhood and later in life.
Crohn"s disease tends to be more common in relatives of patients with Crohn"s disease. It also is more common among relatives of patients with ulcerative colitis.
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. 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 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 patients 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 patients 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.