<unk>  <unk>  is an autosomal dominant inherited condition in which numerous<unk>  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. Three variants are known to exist,<unk>  and attenuated<unk>  (originally called hereditary flat adenoma syndrome) are caused by APC gene defects on chromosome 5 while autosomal recessive<unk>  (or MUTYH-associated polyposis) is caused by defects in the MUTYH gene on chromosome 1. Of the three,<unk>  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. Detection and removal before metastasis outside the colon can greatly reduce and in many cases eliminate the spread of cancer. The root cause of<unk>  is understood to be a genetic mutation—a change in the body's tumour suppressor genes that prevent 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 as a result, and the gene may in some cases still partially operate to control tumours, therefore cancer from<unk>  takes many years to develop and is almost always an adult-onset disease. The second form of<unk> , known as attenuated<unk>  has the APC gene functional but slightly impaired. It is therefore somewhat able to operate as usual. Attenuated<unk>  still presents a high 70% lifetime risk of cancer (as estimated), but typically presents with far fewer polyps (typically 30) rather than the hundreds or thousands usually found in<unk> , and arises at an age when<unk>  is usually no longer considered likely—typically between 40 and 70 years old (average 55) rather than the more usual 30s upward. Because it has far fewer polyps, options for management may be different. The third variant, autosomal recessive<unk>  or MUTYH-associated polyposis, is also milder and, as its name suggests, requires both parents to be 'carriers' to manifest the condition. In some cases<unk>  can manifest higher in the colon than usual (for example, the ascending colon, or proximal to the splenic flexure, or in the stomach or duodenum) where they show no symptoms until cancer is present and greatly advanced. APC mutations have been linked to certain other cancers such as thyroid cancer. As the mutation causing<unk>  is autosomal dominant, it can be inherited directly from either parent to a child. A genetic blood test of the APC gene exists that can determine whether it is present, and therefore can predict the possibility of<unk> . Individuals at risk (due to family links or genetic testing) are usually offered routine monitoring of the intestinal tract every 1–3 years for life, from puberty for<unk>  and early adulthood for attenuated forms. Colon resection surgery is recommended if numerous colon polyps are found due to high risk of early death from colon cancer. International polyposis registries exist that track known cases of<unk>  or APC gene defects, for research and clinical purposes. Mutation of APC also occurs commonly in incident cases of colorectal carcinoma, emphasizing its importance in this form of cancer.
Familial adenomatous polyposis
Hereditary nonpolyposis colorectal cancer
Juvenile polyposis syndrome
MUTYH-associated polyposis
Serrated polyposis syndrome
Pseudopolyps
Ogden syndrome
Polymerase proofreading-associated polyposis