The minimum number of polyps necessary for a diagnosis of Familial Adenomatous Polyposis (FAP) is:
## **Core Concept**
Familial Adenomatous Polyposis (FAP) is an autosomal dominant genetic disorder characterized by the development of hundreds to thousands of polyps in the colon and rectum. It is caused by mutations in the **APC gene** and significantly increases the risk of colorectal cancer. The diagnosis is primarily based on the number of polyps observed.
## **Why the Correct Answer is Right**
The correct answer, **>100 polyps**, is based on the clinical criteria for diagnosing FAP. Patients with FAP typically develop more than 100 adenomatous polyps throughout their colon and rectum. The presence of such a high number of polyps is highly suggestive of FAP, and it distinguishes the condition from other polyposis syndromes or sporadic cases of colorectal polyps. The **APC gene mutation** is identified in most cases, further confirming the diagnosis.
## **Why Each Wrong Option is Incorrect**
- **Option A: >10 polyps**. This number is too low for a diagnosis of FAP, as it could be seen in various other conditions, including sporadic cases of colorectal polyps.
- **Option B: >50 polyps**. While a significant number of polyps, this is still below the typical threshold for diagnosing FAP.
- **Option D: >1000 polyps**. Although patients with FAP can have over 1000 polyps, the diagnosis can be made with fewer polyps, making this option not necessary for a definitive diagnosis.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that FAP patients are at extremely high risk of developing **colorectal cancer** by age 40-50 if left untreated. Therefore, prophylactic **colectomy** is often recommended. Early diagnosis through screening and genetic testing is crucial for preventing cancer.
## **Correct Answer: B. >100 polyps**