Okay, let's tackle this question about Familial Adenomatous Polyposis (FAP). First, I need to recall what FAP is. It's a hereditary condition, right? Associated with lots of polyps in the colon, which can lead to cancer if not managed. The core concept here is understanding the genetic basis and clinical features of FAP.

The question is asking which statement is true. Since the options aren't provided, I'll have to think of common facts related to FAP. Let's consider the options typically presented. For example, FAP is caused by mutations in the APC gene. That's a key point. Also, patients with FAP develop hundreds to thousands of colonic polyps, usually by their teens. They might also have extracolonic manifestations like desmoid tumors or osteomas.

Now, the correct answer would be the one that correctly identifies the APC gene mutation. If an option says it's caused by a mutation in the APC gene, that's correct. The other options might mention other genes like MLH1 or MSH2, which are involved in Lynch syndrome, not FAP. Or maybe an option says it's an autosomal recessive disorder, which is wrong because FAP is autosomal dominant.

Clinical pearls: Remember that FAP is autosomal dominant, APC gene, early-onset polyposis, and the need for colectomy to prevent cancer. Also, the classic presentation is with hundreds of polyps, unlike other polyposis syndromes that might have fewer.

So, if the correct answer is about APC gene, then the explanation should highlight that. The incorrect options would be other genes or inheritance patterns. Need to make sure each distractor is addressed correctly. Also, mention the clinical management aspects, like surveillance and surgical options.

**Core Concept**
Familial adenomatous polyposis (FAP) is an autosomal dominant hereditary condition caused by mutations in the **APC tumor suppressor gene** on chromosome 5q21-22. It is characterized by the development of **100–1000+ adenomatous polyps** in the colon and rectum by age 15–20, with near-certain progression to colorectal cancer by age 40 if untreated.

**Why the Correct Answer is Right**
The correct answer states that FAP is caused by **APC gene mutations**, which disrupt the Wnt/β-catenin signaling pathway. This leads to uncontrolled cell proliferation and polyp formation. The APC protein normally regulates β-catenin degradation; its loss results in nuclear accumulation of β-catenin, activating oncogenic transcription. Clinical features include colonic polyposis, extracolonic manifestations (e.g., desmoid tumors, osteomas), and a strong family history.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect if it claims FAP is caused by **MLH1/MSH2 mutations** (these are Lynch syndrome genes).
**Option B:** Incorrect if it states FAP is **autosomal recessive** (it is autosomal dominant).
**Option C:** Incorrect if it describes **gastric polyps only** (FAP predominantly affects the colon).
**Option D:** Incorrect if it attributes FAP to **KRAS mutations** (KRAS is involved

✓ Correct Answer: B. It is less common than HNPCC