Introduction
Etiology is the term used in medicine to describe the cause or reason
for the development of a disease or condition. My patients who are newly
diagnosed with either ulcerative colitis (UC) or Crohn’s disease
(CD) are often concerned about how they developed these diseases and what
it means to their future and their families. They want to know what causes
it, and if there is anything they did to provoke the illness. They would
like to know if there is anything they can do to prevent anyone else in
the family from developing the same problems.
It is very important to note at the start of this newsletter that we
do not know what truly causes UC or CD (known together as Inflammatory
Bowel Disease or IBD). It is also important that you realize you are not
to blame for your disease. However, there are steps you can take to treat your
symptoms and multiple medications available today for IBD. For more information
on what you can do as a patient to control your symptoms, please refer
to the newsletter by Dr. Hanauer, "Staying on Medication –
Your Health Depends On It," which is available by clicking on the
link on the right side of this page.
In this newsletter, I will address some of the factors that could possibly
be attributed to developing IBD. I will also answer some of the most common
questions I receive from my patients regarding the cause of IBD and if
there is anything they can do to prevent others close to them from getting
it.
What Causes IBD?
As I stated above, at this time we do not fully understand what causes
UC and CD. We do know that these are complex conditions, which are influenced
by genetic, environmental, and immune system factors. However, at this
time we do not know how much importance to attribute to each of these
factors.
We do know that genetic factors play a major role in determining who
is susceptible to IBD. It clusters in families and, in fact, the presence
of a positive family history outweighs all other known risk factors for
the future development of IBD.
Genetic Factors
Studies of first-degree relatives (parents, children, and siblings) and
of twins have taught us that if one member of the family has UC, the risk
that another first-degree relative has or will develop the disease is
8-15 times more likely than that of an unrelated person. The increased
risk for CD is 20-35 times more likely among first-degree relatives than
among unrelated persons. The genetic linkage for CD is greater than that
for UC and much greater than that for other common genetically linked
diseases, such as type 1 diabetes or hypertension.
Some ethnic groups are at increased risk for IBD as well, which also
points to a genetic role in development of these illnesses. Jewish people
of European descent (often called Ashkenazi Jews) are 2-9 times more likely
to contract IBD compared with their non-Jewish neighbors irrespective
of diet or religious observances. Caucasians and African Americans are
more likely to have IBD than Hispanics or Asians, although recently CD
has become more common in the Japanese. Another fact pointing to a genetic
role is that individuals who have certain other diseases that tend to
run in families, such as psoriasis, also develop IBD more frequently.
Complex mutations, or alterations, of several genes appear to contribute
to the development of IBD. For example, patients who have two mutations,
which is the minimum number commonly thought necessary to develop CD,
still may not develop CD because an environmental trigger is absent. It
is not a simple genetic factor like the development of blue eyes or brown
eyes. Nonspecific genes are believed to increase the risk for inflammation
that characterizes IBD in general, while others relate more specifically
to either UC or CD.
As you should be aware, IBD is a complex disorder in which multiple
genes place people at increased risk for developing the disease. Additional
information about IBD and genetics is available on the Internet at www.ibd.patientcommunity.com
and other Web sites.
Environmental Factors
Our understanding of the relationship between genetics and IBD is far
from complete. While our understanding of environmental factors is also
incomplete, some specific risk factors that predispose patients to developing
IBD are known. An example is cigarette smoking, which is a significant
risk factor for CD but not for UC. CD patients who smoke have a more severe
disease course and a more rapid recurrence rate after surgical intervention.
Conversely, cigarette smoking may be somewhat protective against the
development of UC, and stopping smoking may trigger the onset of the disease.
The nicotine in tobacco may be the major factor, but using the nicotine
patch in UC patients provides only minimal relief. Because tobacco, in
any form, places people at a high risk for other serious, life-threatening
diseases I do not routinely recommend it to my patients as a strategy
for controlling IBD.
Bacteria and viruses have also been implicated in the development of
IBD. The intestine normally contains large numbers of both "good
and bad bacteria." Healthy people typically experience no health
consequences from these bacteria. However, in people with IBD, common
types of bacteria may actually cause harm to the wall of their intestines
and trigger the inflammation in IBD.
Use of nonsteroidal anti-inflammatory drugs (NSAIDS), such as the various
brands of ibuprofen and naproxen, may be a major factor in triggering
IBD. While not all studies have implicated NSAIDS, in one recent study
nearly a third of patients experienced either a relapse or the onset of
their illness shortly after taking NSAIDS. I ask all of my IBD patients
to contact me prior to using these medicines to see if they are truly
required; you should discuss them with your doctor as well. More information
about the role of NSAIDS and infectious agents and IBD can be found at
www.ibd.patientcommunity.com
and www.medicinenet.com.
IBD is more common among people living in developed countries than those
living in less developed countries and in people living in urban rather
than rural areas. It is also somewhat more common among individuals with
a higher socioeconomic status. The incidence of IBD increases among people
who emigrate from low-risk geographic areas to high-risk geographic areas.
Such observations provide further evidence that environmental factors
play an important role in the development of IBD. One theory is that children
in underdeveloped countries may be exposed to infections that are not
common in developed countries. This exposure may lead to a more resistant
immune system that prevents the subsequent development of IBD.
Because environment is a factor, there has been speculation about the
role of diet in the development of IBD. At the present time, research
has not demonstrated a major role for diet. Nonetheless, much is made
of diet, especially through the Internet and news media. Little evidence
exists to support these claims. You can discuss dietary options with your
physician and also visit www.ccfa.org/research/info/diet.
Immune System Factors
The two major factors, namely genetics and environment, are now linked
to a third factor: patients with IBD have a disturbance in their normal
mucosal immune function. For example, it’s the role of the body’s
immune system to respond to microorganisms in the diet. Our normal immune
system will react when it is threatened by a harmful bacteria or virus.
In patients with IBD, however, the immune system tends to overrespond
to these threatening agents and, rather than quieting down after the threat
has subsided, it continues to overreact, which results in continued inflammation.
Now I’ll answer some of the specific questions that my patients
ask regarding etiology.
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Frequently Asked Questions
How did I get this disease?
Currently the cause of IBD is believed to be a complex combination of
genetic susceptibility and environmental triggers that result in an overreactive
immune response. We really cannot be sure at this time how an individual
acquires IBD, and it is probably not the same cause for each patient.
The most important thing that I can tell you is that you are not to blame.
While stress can aggravate IBD, you did not develop UC or CD because
you worry too much, work too hard, or eat the wrong foods. However, if
you have CD and you are a smoker, I suggest you try to quit immediately.
Additionally, when you develop this illness you must continue to take
your medicines as prescribed by your physician. As I mentioned earlier,
Dr. Hanauer’s newsletter stressed the importance of maintaining
health through proper use of medication. Even though you did nothing wrong
to develop IBD, you must commit yourself to your own wellness to keep
it under control.
Is IBD contagious?
The answer is simply, "No. IBD is not contagious." These diseases
do not spread through human contact. Developing IBD is a complex combination
of genetic, environmental, and immune system factors.
If genetics plays a role, what are the chances that I am going
to pass this disease to my children?
Specific genes associated with IBD vulnerability have recently been identified
on several chromosomes. We know more about some of these genes than others.
No defined mode of inheritance has been found, but we think that two or
more susceptible genes are required for an inherited risk for IBD to occur.
Among Caucasians, we estimate the risk to children of one affected parent
to be 5-10%. The risk to children of two affected parents is over one-third
and may be as high as 50%. The risk is higher when there is a strong family
history of IBD, when IBD has occurred at an early age, and when the family
is of Jewish descent. Unfortunately, insufficient data is available to
accurately calculate the risk in non-Caucasian families.
Can I do something to prevent other members of my family from
getting IBD?
We do not have strong recommendations for preventing IBD because we do
not know exactly what causes it, but several actions may be helpful.
We feel that smoking is bad for everyone. If you have CD, avoid tobacco
smoke. Both tobacco smoking and possibly exposure to second-hand smoke
may increase your family’s risk.
Theoretically, if you have a strong family history of IBD it might be
helpful to limit your family’s use of NSAIDS. While these have not
been shown to cause IBD, they have been associated with damage to the
wall of the intestines as well as with relapses in patients who already
have IBD. Your doctor should be consulted on the advisability of using
NSAIDS for any specific illness. Do not use them indiscriminately.
Should I, or other members of my family, have genetic testing?
At this point, I do not recommend genetic testing for most people. Screening
of unaffected individuals is not very helpful because genetic tests at
this time cannot accurately predict or rule out the possibility of developing
disease.
The likelihood of a positive genetic predisposition varies widely and
is affected by race, ethnicity, and environment, as well as the number
of people in the family affected by the disease. At this time genetic
testing is considered a research tool and is not used routinely. However,
I hope this recommendation will change in the future as more specific
genetic information is discovered.
I have heard that people born between September and February
are more likely to have IBD. Is this true?
Population-based studies have suggested a higher prevalence of IBD among
people born in certain months; however, many of these studies contained
errors that when corrected have failed to demonstrate a significant relationship
between birth month and IBD. Seasonal patterns and relapse of IBD may
occur for some people. Unfortunately, it is difficult to reach final conclusions
from this information because the number of patients studied is small
and the seasons in which relapse is most frequent vary from country to
country. However, the presence of seasonal variation does support the
view that environmental factors play a significant role in IBD.
Does having IBD increase my risk for any other diseases?
Unfortunately, yes. But the good news is that many of these diseases are
treatable. One of the most common problems is anemia, a deficiency in
red blood cells that affects about half of all IBD sufferers. This may
require treatment with iron, folic acid, or vitamin B12.
Individuals with IBD have an increased risk of developing several types
of arthritis. One form affects the spine but does not usually cause deformities.
Another type affects knees, wrists, elbows, and ankles. Fortunately, this
type of arthritis is self-limited and disappears with treatment of the
IBD.
IBD is associated with skin disorders, such as psoriasis, erythema nodosum
(painful bumps on the skin) and pyoderma (ulceration of the skin). A small
percentage of patients will develop eye inflammation. These are all treatable
conditions that should be discussed with your physician.
People with IBD experience a somewhat increased incidence of thrombosis
(blood clots) as well as an increased incidence of kidney stones and gallstones.
A significant illness called sclerosing cholangitis, in which the liver
ducts become narrowed, occurs in a small percentage of patients. The most
serious illness for which IBD sufferers have an increased risk is colorectal
cancer. Subsequent issues of this newsletter will cover risk from other
diseases and complications of IBD in greater detail.
What about cancer?
IBD patients do have an increased risk for colorectal cancer. The greatest
risk is in those patients who have the most extensive forms of colitis
and who have had the disease for the longest duration. The risk is also
increased in patients with a family history of colon cancer and in those
with sclerosing cholangitis.
The overall prevalence of colorectal cancer in patients with IBD is
approximately 4%, but risk increases over time with a 2% incidence of
cancer after 10 years, a 9% incidence after 20 years, and a 19% incidence
after 30 years of disease.
However, the good news is that colorectal cancer is one of the most
preventable and treatable cancers through lifestyle changes and early
detection. Exercising regularly and eating healthfully to maintain normal
weight, avoiding tobacco, and staying on your medication are important
things you can do to prevent colorectal cancer. The other major thing
you can do is to have regular colorectal cancer screening as recommended
by your doctor. This usually entails a colonoscopy.
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Summary
In summary, the development of IBD is related to genetic and environmental
factors with a subsequent overreactive immune system. But with our current
state of knowledge it is not possible to say exactly how much each element
contributes to disease vulnerability or to predict who will get IBD.
Remember, you are not to blame for your disease and the disease is not contagious.
Relationships between IBD and food, stress, seasonal variation, and infectious
agents have not been established. More research is needed to verify, or
rule out, the many environmental factors that have been proposed as potential
culprits.
Despite this uncertainty, we have come a long way in increasing our knowledge
of the causes and treatments for IBD. There are multiple effective treatments
available today for both UC and CD so please discuss these with your physician
and take these medications as they are prescribed for you. The approximately
one million people living with IBD in America today have better care and
prospects for longer, more satisfying lives than ever before.
The next newsletter, Volume 3, "The Clinical Course of IBD" will
discuss how IBD affects patients over time including its effects on parts
of the body other than the intestines, as well as common complications and
how you can help to control them.
This information has been reviewed and approved by CCFA's National Scientific Advisory Committee.
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