general white population or Jews who trace their origins
to other regions. Internationally, Crohn’s disease is rare
in Africa, Asia, and South America. It is more common
in urban areas than in rural areas, suggesting that envi-
ronment plays a role in the disease.
Causes and symptoms
At one time, researchers thought that stress and
diet caused Crohn’s disease. Now researchers know
that these are not factors, although both stress and diet
can worsen symptoms in people who already have the
disease. What researchers do know is that Crohn’s
disease is caused by an inappropriate immune system
reaction that affects cells in the digestive tract. Beyond
that, the reasons why some people develop the disease
are not clear.
There is almost certainly an inherited component
that predisposes some people to the disease. Individu-
als who are blood relatives of a parent, sibling, or child
with Crohn’s disease are 30 times more likely to
develop the disease than the general population. Sci-
entists believe multiple genes are involved in develop-
ment of the disease. However, more than genetics
determines who gets Crohn’s disease, because only
about 44% of identical twins both develop the disease.
Researchers have found several mutated (altered)
genes in many, but not all, people who have Crohn’s
disease but do not yet have a clear understanding of
what these genes do.
Current thinking is that interplay between genes,
the environment, the individual’s health, and body
chemistry affect who develops Crohn’s disease.
When foreign materials (antigens) enter the body, the
immune system produces antibodies, which are pro-
teins that neutralize the foreign invader. One theory
about Crohn’s disease is that some foreign organism
or material stimulates an immune system response in
the digestive system, and then through an error in
genetic control, the response cannot be ‘‘turned off.’’
A second theory suggests that the cells of the immune
system mistake good bacteria, food, or some other
substance that is normally present in the digestive
tract and make antibodies against this material as if
it were a foreign substance. Either way, an inappro-
priate immune system response occurs that appears to
be the root cause for the symptoms people with
Crohn’s disease experience.
Symptoms of Crohn’s disease vary, depending on
the location of the damaged cells and the length of
time the individual has had the disease. Symptoms can
be mild or severe. They can develop suddenly or grad-
ually, and they may improve or even disappear, and
then worsen many times throughout an individual’s
life. In general, symptoms can be divided into thoseSmall intestine (lower right) infected by Crohn’s disease.(John
Bavosi/Photo Researchers, Inc. Reproduced by permission.)
KEY TERMS
Abscess—A pocket of pus formed by an infection.
Antibody—A protein produced by the immune sys-
tem to fight infection or rid the body of foreign
material. The foreign material that stimulates the
production of antibodies is called an antigen. Spe-
cific antibodies are produced in response to each
different antigen and can only inactivate that par-
ticular antigen.
Anus—The opening from the rectum to the outside
of the body through which stools pass. The open-
ing and closing of the anus is controlled by a
strong ring of muscles under somewhat voluntary
control.
Mineral—An inorganic substance found in the
earth that is necessary in small quantities for the
body to maintain a health. Examples: zinc, copper,
iron.
Vitamin—A nutrient that the body needs in small
amounts to remain healthy but that the body cannot
manufacture for itself and must acquire through
diet.Crohn’s disease