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Familial Adenomatous Polyposis - An Overview

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Familial adenomatous polyposis is mainly an autosomal dominant genetic disorder affecting the colon. Read the article to know more about the condition.

Medically reviewed by

Dr. Ghulam Fareed

Published At February 17, 2023
Reviewed AtJuly 11, 2023

Introduction:

Familial adenomatous polyposis is an autosomal dominant polyposis syndrome with a variable degree of penetration. It is also known as familial polyposis coli (FPC). If the condition is left untreated, hundreds or thousands of polyps develop in the colon and rectum of the individual. The polyps start developing in teenagers and tend to develop into colorectal cancer by forty.

The treatment of choice for reducing the chances of colorectal cancer is colectomy. Familial adenomatous polyposis also correlates with other cancers of the gastrointestinal region, such as gastric, hepatoblastoma, duodenal, and desmoid tumors. The underlying genetic defect in familial adenomatous polyposis is a germline mutation in the APC (adenomatous polyposis gene). It has been observed over the years that FAP (familial adenomatous polyposis) has variable phenotype expressions, which include the Turcot syndrome and Gardner syndromes.

What Is the Cause of Familial Adenomatous Polyposis?

The mutation causes familial adenomatous polyposis at the APC (adenomatous polyposis gene) on chromosome 5. The gene is a tumor suppressor gene; most mutations are nonsense mutations. Therefore, the phenotype and genotype of the gene vary. The gene mutation location is responsible for the phenotypic variation and the development of the disease's extracolonic manifestations.

What Is the Prevalence of Familial Adenomatous Polyposis?

Familial adenomatous polyposis occurs in 1 in every 10000 individuals, and it is the second most common inherited colorectal cancer syndrome. About 30 % of cases of familial adenomatous polyposis have an unknown family history and represent adenomatous polyposis gene mutation. The disease also has a milder form known as attenuated familial adenomatous polyposis (AFAP), which may contribute to colorectal cancer. Patients suffering from attenuated adenomatous polyposis have an almost 70 % chance of developing colorectal cancer.

What Are the Symptoms Seen in Familial Adenomatous Polyposis?

The clinical appearance of the disease familial adenomatous polyposis varies depending on the person's family history. Patients who have a known family history of familial adenomatous polyposis should start getting a screening done at a young age with an annual endoscopy evaluation. Patients with no family history often present with colorectal cancer during screening colonoscopy or at a very young age.

  • Many patients present with nonspecific symptoms such as abdominal discomfort, rectal bleeding, or diarrhea.

  • Physical examination also states congenital retinal epithelium's congenital hypertrophy in familial adenomatous polyposis.

  • In some cases of Gardner syndrome, the patient may have osteomas of the mandible or skull.

  • Abnormalities seen in dentition due to APC (adenomatous polyposis gene) mutation are supernumerary teeth, impacted teeth, cysts, and odontomas.

  • Young children may have several epidermoid cysts on the face, extremities, and scalp. Epidermoid cysts are small non-cancerous bumps that arise beneath the skin. These cysts are slow-growing and are often painless.

  • Some patients may have fibromas on the back, trunk, and extremities. Fibromas are benign tumors that are composed of fibrous tissue and connective tissue. Fibromas can grow on all organs and arise from mesenchymal tissue.

What Are the Extracolonic Manifestations of Familial Adenomatous Polyposis?

  • Desmoid: These are solid connective tissue tumors that can be invasive and grow very large. The tumors are rare but affect about 10 % to 15 % of familial adenomatous polyposis. The incidence of occurrence is more in the abdominal cavity. Desmoid tumors are firm, large, and painless masses with irregular margins.

  • Gastric or Duodenal Polyps: Gastric polyps account for almost 90 % of patients with familial adenomatous polyposis, but they have less potential to develop into adenocarcinoma. It was reported that only 1 % of gastric polyps turn into cancer.

  • Thyroid: Papillary carcinoma is the most common thyroid cancer in familial adenomatous polyposis. Thyroid cancer can occur in approximately 2 % of cases of familial adenomatous polyposis. The chances of thyroid cancer are higher in women as they account for almost 90 % of familial adenomatous polyposis, which may develop thyroid cancer.

  • Hepatoblastoma: The chances of hepatoblastoma in patients of familial adenomatous polyposis are very low and can occur more commonly in children (males) under the age of 5 years.

What Is the Diagnosis of Familial Adenomatous Polyposis?

Patients with a family history of familial adenomatous polyposis should have annual endoscopy and flexible sigmoidoscopy or colonoscopy from 10 to 12 years old. The evaluation should be carried out until the polyp load of the colon is controlled by endoscopic removal. Genetic testing is not preferred at the early age of the patient as there is a psychological burden on the patient for positive results. Genetic testing should be carried out only after clinical confirmation of familial adenomatous polyposis.

What Is the Treatment for Familial Adenomatous Polyposis?

The surgical options for treating familial adenomatous polyposis include subtotal colectomy with ileostomy, subtotal colectomy with ileorectal anastomosis, or total proctocolectomy with ileoanal pouch.

  • Subtotal colectomy is a less challenging surgical procedure but requires regular evaluation of the rectum. The rectal mucosa is at significant risk of developing adenocarcinomas. If the rectum is safe and intact, endoscopic surveillance can be performed at a regular interval of six months because the risk of rectal cancer is almost 29 % by age 50.

  • Total proctocolectomy is done by removing the colon and rectum with either the ileostomy or creating an ileoanal pouch. Regular evaluation is not required in this procedure; however, there are disadvantages, such as an increased chance of infertility in men and women and urinary dysfunctions. The patient also feels increased stool urgency with an ileoanal pouch.

  • Non-surgical treatment modalities that delay the surgical technique have a limited effect on familial adenomatous polyposis. For example, Sulindac is a nonsteroidal anti-inflammatory drug that, according to the studies, shows an almost 50 % reduction in adenomas and the size of adenomas up to 65 %. But it was also reported that adenomas were recurrence as the Sulindac was discontinued.

  • The selective COX-2 inhibitors at high doses have demonstrated an almost 30 % reduction in adenoma burden.

Conclusion:

Familial adenomatous polyposis is a genetic disorder that is caused due to mutations in the APC (adenomatous polyposis gene) which leads to the formation of hundreds to thousands of polyps in the colon gradually. The condition usually occurs in people who already have a family history of the disease and needs regular surveillance to prevent the severity of the condition. The polyps can also manifest outside the colon and affect the gastric lining, duodenum, hepatic region, and thyroid. The treatment of choice for familial adenomatous polyposis is the surgical removal of the colon, as other techniques, such as medications, may lead to recurrence.

Frequently Asked Questions

1.

How is Familial Adenomatous Polyposis characterized?

Familial adenomatous polyposis (FAP) is a genetic disorder that is characterized by the formation of polyps in the colon and rectum, which are the parts of the large intestine. If these polyps are untreated, they may become cancerous. FAP can also cause desmoid tumors (fibrous and non-cancerous tumors in the upper gastrointestinal tract), gastric polyps, and hepatoblastomas (liver cancer).

2.

What Is the Life Expectancy of an Individual Affected by Familial Adenomatous Polyposis?

Individuals with familial Adenomatous Polyposis can have improved life if they undergo treatment at an early age, such as colectomy, in which the whole colon is removed. Untreated individuals have a short life expectancy and live up to 40 years of age.

3.

How Is APC Gene Related to Familial Adenomatous Polyposis?

Any mutation in the APC (adenomatous polyposis coli) gene, which is located in chromosome 5, results in familial adenomatous polyposis. This gene affects the normal growth of cells and their function. This results in the overgrowth of the cells, resulting in polyps. This type of mutation is inherited in an autosomal dominant pattern in which one mutated gene from one parent is enough to cause this condition.

4.

What Is the Most Common Type of Polyposis Syndrome?

Polyposis syndromes are inherited conditions that have an increased risk of the formation of polyps in the gastrointestinal tract. Some of the polyposis syndromes are FAP, serrated polyposis syndrome (formation of serrated polyps which are irregular in the colon), juvenile polyposis syndrome (formation of many non-cancerous growths in the colon), PTEN-hamartomatous syndromes (a syndrome that occurs due to mutation in the PTEN gene that causes tumors in the colon), MUTYH-associated polyposis (a condition of formation of tumors in the colon due to mutation in the MUTYH gene), and Peutz-Jeghers syndrome (development of growths in the colon along with brownish spots on the lips). Among these types, FAP is the most common one.

5.

What Is the Latest Treatment Included in Familial Adenomatous Polyposis?

The surgical removal of the colon is the standard treatment for FAP. The latest advances are subtotal colectomy with ileorectal anastomosis, where the rectum is not removed, and total proctocolectomy with a continent ileostomy where the rectum and colon are removed, and an ileostomy is made in which an opening of bowel part is made in the abdomen. Other treatments include total proctocolectomy with ileoanal anastomosis, in which the large intestine is removed, and the small intestine is connected to the rectum.

6.

When Should Familial Adenomatous Polyposis Be Tested?

FAP is a genetic disorder and, in case of positive family history, should undergo a colonoscopy from the age of 10 to 12 years every 1 to 2 years. Colonoscopy is a type of diagnostic test where a thin tube is inserted through the anus to examine the large intestine.

7.

Can Adenomatous Polyposis Be Cured?

No, adenomatous polyposis cannot be cured, but treatment is aimed towards improvement of lifestyle and reducing the discomfort and pain. Treatment such as colectomy, where the colon is removed, is the standard treatment for FAP.

8.

Is Familial Adenomatous Polyposis an Autoimmune Disorder?

No, FAP is not an autoimmune disorder where the immune system damages the healthy cells. FAP is a genetic disorder that occurs due to a mutation in the ACP gene, which is inherited in an autosomal dominant manner where one gene is enough to cause the disorder from the parent. This disorder can also occur due to a mutation in the MUTYH (mutY DNA glycosylase) gene, which is inherited in an autosomal dominant manner where two mutated genes from the parent are required to cause the disorder.

9.

What Measures Should Be Taken to Prevent Adenomatous Polyps?

The preventive measures include:


- Incorporating a healthy lifestyle by exercising daily.


- Quitting cigarettes and alcohol.


- Eating fruits and vegetables.


- Avoiding red meat in the diet.


- Incorporating low doses of Aspirin can also help prevent polyp formation in the colon. In addition to these, early screening at the age of 10 should be made to diagnose and prevent further damage caused by FAP.

10.

What Medication Is Used in the Treatment of Familial Adenomatous Polyposis?

The medications that are used are painkillers such as nonsteroidal anti-inflammatory drugs (NSAIDs) and Aspirin. Other drugs that are used are Celecoxib and Sulindac, which are both NSAIDs that help in preventing the growth of polyps.

11.

At What Age Does the Familial Adenomatous Polyposis Occur?

The growth of polyps can occur at an early age, such as between 10 and 19 years. In the case of classical FAP, the polyps can become cancerous till the age of 39 years, and in the case of attenuated FAP, which is a milder form, the polyps can become cancerous till the age of 55 years.

12.

Can a Familial Adenomatous Polyposis Miss a Generation?

No, FAP cannot miss a generation since it is an inherited genetic disorder that can occur in an autosomal dominant and autosomal recessive manner. In the case of autosomal dominant, the child has a 50 % risk of developing the condition. In the case of autosomal recessive, the couple who are carriers have a 25 percent risk of transmitting the syndrome to the child, a 50 percent risk of being carriers by their children, and the other 25 percent of children may have normal genes and are not affected by this condition.

13.

How Cancerous Are Colon Polyps?

Colon polyps are raised bumps on the colon surface, and a polyp has a 5 to 10 % chance of becoming cancerous. A polyp becomes cancerous depending on its size. The larger the polyp, the higher the risk.

14.

What Foods Should Be Avoided in Case of Familial Adenomatous Polyposis?

Individuals with FAP should avoid dairy products, white sugar, alcoholic drinks, processed meat, red meat, sweetened jam, butter, candies, ice creams, and potatoes. The individuals should be on a diet that has high fiber content, vegetables, and fruits.

15.

What Are the Clinical Diagnostic Criteria for Familial Adenomatous Polyposis?

The diagnostic criteria for FAP include the detection of 10 or more than 100 polyps in the large intestine. As the person ages, the polyps also increase, and at the age of 39, in the case of classic FAP, hundreds to thousands of polyps are suspected and are also turned into cancerous.

16.

What Is the Growth Rate of Polyps?

A polyp can increase its volume by 20 % every year. However, some polyps can persist in being small or regress in their size. Cancerous polyps grow at a slower rate, and for a polyp to become cancerous, it can take an average of 10 years.

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Dr. Ghulam Fareed
Dr. Ghulam Fareed

Medical Gastroenterology

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