classic familial adenomatous polyposis

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant inherited condition in which numerous adenomatous polyps form mainly in the epithelium of the large intestine. While these polyps start out benign, malignant transformation into colon cancer occurs when they are left untreated. Besides classical FAP, there is one attenuated FAP variant (originally called hereditary flat adenoma syndrome) are caused by APC gene defects on chromosome 5. While another polyposis-related syndrome, MUTYH-associated polyposis(MAP), is caused by defect in the MUTYH gene on chromosome 1, rather than APC gene. The root cause of FAP is understood to be a genetic mutation—a change in the body's tumour suppressor genes that prevent the development of tumours. 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). These gene changes do not trigger cancer, but rather, they reduce the body's ability to prevent cells from becoming cancerous. Even with the gene change, it may still take time before a cell actually does develop that is cancerous one as a result, and the gene may, in some cases, still partially operate to control tumours. Cancer from FAP takes many years to develop and is almost always an adult-onset disease. The milder form of FAP, known as attenuated familial adenomatous polyposis has the APC gene functional but slightly impaired. It is therefore...