Gardner Syndrome (cont.)
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.
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