An Introduction to FAP

Familial Adenomatous Polyposis, FAP, has been studied for over a century, but it wasn't until after the 1980's that anything about the disease's genetics was known.  In 1987, researchers narrowed down the location of the gene responsible for FAP to the long arm of chromosome 5.  This information was very helpful in the identification of the entire gene, which occurred in 1992 by a group from King's College School of Medicine. The gene was eventually named APC, Adenomatous Polyposis Coli, and became a poster-gene for cancer genetics.

The APC gene is comprised of roughly 139,000 base-pairs, and its translated protein product contains 2,843 amino acids.  It's 15 exons can be alternatively spliced into 30 different mRNAs of roughly similar shape and function.  There are 40 distinct introns that are cleaved from the mRNA product before the 15 exons are pasted together to form the final protein product.

FAP is identified in patients via genetic tests, as well as by identifying abnormally large numbers of polyps in intestinal tissues, especially the large intestine/colon.  A patient with FAP has a near-100% chance of developing colon cancer by the age of 40 or 50 years old.  There is no way to prevent the formation of these polyps or their progression to tumors.  The only protection against FAP colon cancer is regular colonoscopies or a serious surgery that removes the entire colon but maintains rectal function for natural waste removal.


FAP is inherited in dominant fashion.  That means, that where a parent with FAP has a 50% chance of passing the disease along to each of his or her children.  When a child does not inherit a mutant allele from an affected parent, that child has no chance of passing along the disease to his or her progeny.  This tells us that two dysfunctional APC alleles are necessary for the manifestation of this disease.