What is familial adenomatous polyposis?
Familial adenomatous polyposis (FAP) is an inherited disorder
characterized by cancer of the
large intestine (colon) and
rectum. People with the classic type of familial adenomatous polyposis may
begin to develop multiple noncancerous (benign)
growths (polyps) in the colon as early as their
teenage years. Unless the
colon is removed, these polyps will become malignant (cancerous). The average
age at which an individual develops colon cancer in classic familial adenomatous
polyposis is 39 years. Some people have a variant of the disorder, called
attenuated familial adenomatous polyposis, in which
polyp growth is delayed. The
average age of colorectal cancer onset for attenuated familial adenomatous
polyposis is 55 years.
In people with classic familial adenomatous polyposis, the number of polyps
increases with age, and hundreds to thousands of polyps can develop in the
colon. Also of particular significance are noncancerous growths called desmoid
tumors. These fibrous tumors usually occur in the tissue covering the intestines
and may be provoked by surgery to remove the colon. Desmoid tumors tend to recur
after they are surgically removed. In both classic familial adenomatous
polyposis and its attenuated variant, benign and malignant tumors are sometimes
found in other places in the body, including the
duodenum (a section of the
small intestine),
stomach, bones, skin, and other tissues. People who have
colon polyps as well as growths outside the colon are sometimes described as
having Gardner syndrome.
A milder type of familial adenomatous polyposis, called
autosomal recessive
familial adenomatous polyposis, has also been identified. People with the
autosomal recessive type of this disorder have fewer polyps than those with the
classic type. Fewer than 100 polyps typically develop, rather than hundreds or
thousands. The autosomal recessive type of this disorder is caused by mutations
in a different gene than the
classic and attenuated types of familial adenomatous polyposis.
How common is familial adenomatous polyposis?
The reported incidence of familial adenomatous polyposis varies from 1 in
7,000 to 1 in 22,000 individuals.
What genes are related to familial adenomatous
polyposis?
Mutations in the APC gene cause both classic and attenuated familial
adenomatous polyposis. These mutations affect the ability of the cell to
maintain normal growth and function. Cell overgrowth resulting from mutations in
the APC gene leads to the colon polyps seen in familial adenomatous polyposis.
Although most people with mutations in the APC gene will develop colorectal
cancer, the number of polyps and the time frame in which they become malignant
depend on the location of the
mutation in the gene.
Mutations in the MUTYH
gene cause autosomal recessive familial adenomatous polyposis (also called MYH-associated
polyposis). Mutations in this gene prevent cells from correcting mistakes that
are made when DNA is copied
(DNA
replication) in preparation
for cell division. As these mistakes build up in a person’s DNA, the likelihood
of cell overgrowth increases, leading to colon polyps and the possibility of
colon cancer.
How do people inherit familial adenomatous
polyposis?
Familial adenomatous polyposis can have different inheritance patterns.
When familial adenomatous polyposis results from mutations in the APC gene,
it is inherited in an autosomal
dominant pattern, which means one copy of the altered gene in each cell is
sufficient to cause the disorder. In most cases, an affected person has one
parent with the condition.
When familial adenomatous polyposis results from mutations in the MUTYH gene,
it is inherited in an autosomal recessive pattern, which means both copies of
the gene in each cell have mutations. Most often, the parents of an individual
with an autosomal recessive condition each carry one copy of the mutated gene,
but do not show signs and symptoms of the condition.
QUESTION
Bowel regularity means a bowel movement every day.
See Answer
Where can I find information about treatment
for familial adenomatous polyposis?
These resources address the management of familial adenomatous polyposis and
may include treatment providers.
What other names do people use for familial
adenomatous polyposis?
- Adenomatous Polyposis Coli
- Adenomatous Polyposis of the Colon
- Colon
Cancer, Familial - Familial Intestinal Polyposis
- Familial Multiple Polyposis
- Familial
Multiple Polyposis Syndrome - Familial Polyposis Coli
- Familial Polyposis Syndrome
- FAP
- Hereditary Polyposis Coli
- MYH-associated
Polyposis - Polyposis Coli
SOURCE: Genetics Home Reference, National Institutes of
Health