The second form of FAP, known as attenuated familial adenomatous polyposis has the APC gene functional but slightly impaired. Even with the gene change, it may still take time before a cell actually does develop that is cancerous as a result, and the gene may in some cases still partially operate to control tumours, therefore cancer from FAP takes many years to develop and is almost always an adult-onset disease. These gene changes do not trigger cancer, but rather, they reduce the body's ability to prevent cells from becoming cancerous.
The change allows numerous cells of the intestinal wall to develop into potentially cancerous polyps when they would usually reach the end of their life inevitably one or more will eventually progress and give rise to cancer (7% risk by age 21, rising to 87% by age 45 and 93% by age 50). The root cause of FAP is understood to be a genetic mutation-a change in the body's tumour suppressor genes that prevent development of tumours. Detection and removal before metastasis outside the colon can greatly reduce and in many cases eliminate the spread of cancer. Of the three, FAP itself is the most severe and most common although for all three, the resulting colonic polyps and cancers are initially confined to the colon wall. Three variants are known to exist, FAP and attenuated FAP (originally called hereditary flat adenoma syndrome ) are caused by APC gene defects on chromosome 5 while autosomal recessive FAP (or MUTYH-associated polyposis) is caused by defects in the MUTYH gene on chromosome 1. While these polyps start out benign, malignant transformation into colon cancer occurs when they are left untreated.
Lynch syndrome, MUTYH-associated polyposisįamilial adenomatous polyposis ( FAP) is an autosomal dominant inherited condition in which numerous adenomatous polyps form mainly in the epithelium of the large intestine. Medical condition Familial adenomatous polyposisĮndoscopic image of sigmoid colon of patient with familial adenomatous polyposis
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