Familial adenomatous polyposis definition - medical term
Abbreviated FAP. A syndrome char acterized
by the formation of thousands of polyps in the colon and rectum with colorectal
cancer the inevitable consequence. Polyps can also occur in the stomach, duodenum
and the terminal ileum.
The polyps most often begin to form at puberty. And colon cancer usually occurs
10 to 15 years thereafter. The average age of diagnosis of familial polyposis is
25 years of age, with cancers developing at age 20 to 30. However, cancers may arise
anywhere from late childhood to the sixties.
The syndrome is an autosomal dominant disorder with high penetrance and highly
variable expressivity. A person with the disease thus has a 50% chance of passing
the gene on to each of their children. Most people who receive the gene almost always
manifest the disease although the expression of the disease can vary markedly from
person to person.
The gene that is mutated in this disorder, symbolized APC for adenomatous polyposis
coli, has been characterized and its protein identified. A variety of mutations
in the APC gene have also been identified. The APC gene maps to chromosome 5 in
region 5q21-q22.
Gardner syndrome (with polyps of the colon, extra bowel tumors, especially osteomas,
and a rather characteristic abnormality of the retina of the eye) is now known not
to be a wholly different disease but rather to be a variant of FAP, caused by a
mutation in the APC gene.
Familial adenomatous polyposis (FAP) has also been called multiple polyposis
of the colon, hereditary polyposis coli, familial multiple polyposis, familial polyposis
of the colon (FPC) and adenomatous polyposis coli. The designation familial adenomatous
polyposis (FAP) is most often used today, based in part on the appreciation that
the polyps are not confined to the colon.
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