Familial Adenomatous Polyposis - An Overview

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.