Familial Adenomatous Polyposis


What is familial adenomatous polyposis?

In the intestinal tract, polyps are formed which initially affects the colon, the part of the large intestine and rectum. The development of the familial adenomatous polyposis is due to abnormal functioning of the APC gene.

familial adenomatous polyposis fap intestines abdomen


APC gene is involved in controlling cell growth. Most of the cases, familial adenomatous polyposis (FAP) is inherited from any of the parenteral abnormal gene mutation. But in some cases, during conception abnormality in APC gene mutation occurs without having any parental involvement with FAP.

The adenomatous polyposis are cancerous in nature, undetected or untreated condition often causes cancer in the colon or rectum. This can be averted by early diagnosis with proper treatment.

Sign & Symptoms

Usually FAP is asymptomatic in an initial stage. When the number of polyps increases and may turn to cancerous growth after a certain period, then following symptoms may arise:


  • Fresh blood found in the stool
  • Loose stool
  • Constipation /diarrhoea without having any illness or dietary change
  • Abdominal spasm
  • Flatulence
  • Sudden weight loss without having any specific reason
  • Lethargy
  • Red blood cells count decreases (anaemia)

Additional sign & symptoms arise when chances of extracolonic manifestations are there, including:

  • Polyps spread to small intestine, duodenum and stomach
  • Bony outer growth
  • Dental problems
  • CHRPE (congenital hypertrophy of the retinal pigment epithelium)
  • Tumours formation in the soft tissues including fibromas, epidermoid cysts and desmoid tumours.

It is always advisable for safety purpose, parents having FAP, should go for a check up in their children, even without having symptoms in the age of 10 to 12 years of their children. Early diagnosis with genetic testing can identify that if a child has FAP.

Causes

Familial Adenomatous Polyposis is developed due to the presence of germiline at the embryo cell. This germiline formed from abnormal mutation in the Adenomatous Polyposis Coli (APC) gene.

Normally APC gene protects to a cellular overgrowth in the large intestine, but due defective functioning causes polyp formation in the large intestine.

Almost 50% of the cases are inherited; means from affected parent the abnormal gene is transferred to the child. If either parent has FAP, the risk of child to developing the FAP is 50%. Both female and male children have equal risk. If the child is not having any parental history of FAP, then due to new gene abnormally mutate by chance and the onset of FAP occurs.

adenomatosis polyposis gene apc


Image 2 – APC gene

Risk associated for cancerous conversion

Untreated condition always converts FAP to colon or subsequent organ cancer. The chance of conversion of the polyps to malignant tissue is at the age of 20 to 30 years of age. At the age of 40, all untreated FAP convert to cancer.

Diagnosis

There are different possible diagnostic tests are conducted for confirming the Familial Adenomatous Polyposis. The included tests are colonoscopy, genetic testing and flexible sigmoidoscopy.

Usually if a parent has FAP, then routine colonoscopy is conducted every year after the child age is 10 years. This is conducted for early diagnosis. All these tests include some pre-examination preparation, which should be demonstrated by healthcare staff, before conducting the test.

Colonoscopy

In this test the inner lining of the large intestine, including the colon and rectum is diagnosed. For this reason, the patient should take laxative for cleaning the colon region. This provides temporary diarrhoeal event to clean up the whole large intestine. Before initiating the test, doctors usually given a sedative medication for relaxing the patient and this also helps to unaware of the testing procedure which may produce some discomfort to the patient. In colonoscopy, the doctor inserts colonoscope through anal route and examines the inner lining and also takes polyp’s sample for biopsy test.

Genetic testing

In the genetic testing, blood sample is taken from the patient and send it to special laboratory testing, where APC gene mutation is diagnosed. This test is also conducted for screening purpose for a child who has a parenteral history of FAP at the age of 10 -12 years.

Flexible Sigmoidoscopy

Flexible sigmoidoscopy is quite similar to colonoscopy, the only different is that this procedure is conducted only to check the lower portion of the colon including the rectum.

Treatment

The standard therapy, colectomy is usually conducted in Familial Adenomatous Polyposis, where partial or whole colon is removed. This is conducted at the late 20s or 30s of age of the patient.

After conduction of colectomy, if polyps remain in the rectal region, then Sulindac is prescribed. Sulindac is mainly used for treating arthritis, as it is a non-steroidal anti-inflammatory drug (NSAID). Continuous screening is recommended, as the risk of cancer development is always associated.

In case of duodenal polyps, surgery for removing the duodenal polyps is also important for preventing cancerous growth.

Desmoid tumors are non-malignant, but it may constrict the associated abdominal organs and/ or blood vessels. To prevent this, different therapies, including anti-estrogen medications, non-steroidal anti-inflammatory drugs, chemotherapeutic agent, radiation therapy and surgical removal may recommend depending upon the severity.

The family and patient education is very important for early diagnosis and treatment commencement.


References

  1. http://www.medicinenet.com/gardner_syndrome/article.htm
  2. Do colon polyps in FAP always become cancerous?, Can FAP affect other organs? at http://my.clevelandclinic.org/health/diseases_conditions/hic-colorectal-cancer/dd_fap
  3. What are the screening options for classic FAP? at http://www.cancer.net/cancer-types/familial-adenomatous-polyposis
  4. http://www.mayoclinic.org/diseases-conditions/familial-adenomatous-polyposis/basics/definition/con-20035680
  5. https://www4.mdanderson.org/pe/index.cfm?pageName=opendoc&docid=1032
  6. https://rarediseases.org/rare-diseases/familial-adenomatous-polyposis/

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