Familial adenomatous polyposis (FAP) is a rare inherited condition where the large intestine develops a number of precancerous polyps as a result of defect in the adenomatous polyposis coli (APC) gene, it also increases the risk of developing cancer. Most people get the gene from one of their parents. However, the genetic mutation happens naturally in 25–30% of each person.
FAP causes the colon and rectum to develop polyps. Additionally, the upper gastrointestinal tract, particularly the first part of the small intestine, is susceptible to the development of polyps. When the patient is in their 40s, the polyps in their colon and rectum could develop into cancer if left untreated.
Patients with FAP have a nearly 100% lifetime risk of colorectal cancer if they are not treated. The risk of colorectal cancer increases as the patient gets older. The large intestine must typically be surgically removed in order to prevent cancer in those with familial adenomatous polyposis. Duodenal polyps can also develop cancer, but they are typically treatable with close monitoring and routine polyp removal.
The primary symptom of FAP is the development of hundreds or even thousands of polyps in your colon and rectum, which often begin by your mid-teens. By the time you are in your 40s, the polyps certainly will turn into rectal or colon cancer.
Early-stage of colorectal cancer is usually asymptomatic until the disease has progressed to the late stage, but they may include:
- Rectal bleeding, dark stool, or blood in stool
- A constant change in the bowel habit such as diarrhea or constipation
- Abdominal pain
- Unexplained weight loss
In addition to FAP, abnormalities in other area of the body may indicate the presence of FAP. These may include:
- Dental abnormalities (unerupted teeth)
- Cyst of the skin
- Lump on bone of legs, arms, and skull
The APC gene has mutations that affect how well the gene’s protein is supposed to work, which is the cause of the disease. Cells are more likely to develop into cancer as a result of this unregulated cell growth. A mutation in APC was typically passed down from a parent who also had FAP to the majority of patients. A gene abnormality that is typically inherited from a parent is the cause of familial adenomatous polyposis. However, some people are born with the disease-causing gene anomaly.
15% of FAP patients develop desmoid tumors, which are fibrous tissue overgrowths that are rare condition. Sometimes hard, white sheets of desmoid tissue form and cause issues without becoming a tumor. They typically develop inside the abdomen after an abdominal operation and tend to surround the arteries (blood vessels) leading to the colon. This makes their removal challenging or impossible unless a significant portion of the small bowel is also removed. Desmoid tumors frequently recur even after removal. The second most frequent cause of mortality in FAP patients is desmoid disease.
The primary risk to develop familial adenomatous polyposis (FAP) is when someone from the family have this condition such as the parent, or siblings.