Okay, let's tackle this question about Gardner's syndrome. The user wants a detailed explanation for an MCQ where the correct answer is the exception. First, I need to recall what Gardner's syndrome is. It's a genetic disorder, part of the polyposis syndromes, right? So it's related to multiple colorectal polyps and extracolonic manifestations.

The question asks which statement is not true about Gardner's syndrome. The options are A to D, but they're missing here. Wait, the user mentioned the correct answer is provided, but the options are empty. Hmm, maybe the user intended to include options but forgot. But since the correct answer is given as [Letter], I need to proceed with the explanation based on the core concept.

Gardner's syndrome is an autosomal dominant condition caused by mutations in the APC gene. It's a variant of familial adenomatous polyposis (FAP). The key features include multiple adenomatous polyps in the colon, along with extracolonic manifestations like osteomas, epidermoid cysts, and desmoid tumors. There's also an increased risk of colorectal cancer if not treated early.

Now, the incorrect option would be something that doesn't fit. Common misconceptions might include associating it with other syndromes or incorrect inheritance patterns. For example, if an option says it's autosomal recessive, that's wrong. Or if it mentions a different gene like MLH1 instead of APC. Another possible wrong option could be about the type of polyps—Gardner's has adenomas, not hyperplastic or others.

The clinical pearl here is that Gardner's syndrome is part of the FAP spectrum, and early surveillance is crucial. The key is the extracolonic features distinguishing it from classic FAP. So the exception would be an option that contradicts these points.

Putting it all together, the explanation should highlight the core concept, validate the correct answer by explaining the correct features, debunk the wrong options by pointing out inaccuracies, and end with a high-yield fact. Need to make sure each section is concise and fits within the character limit. Also, use proper medical terms and structure as specified.

**Core Concept**
Gardner’s syndrome is an autosomal dominant polyposis syndrome caused by **APC gene mutations**, characterized by **colorectal adenomas**, **osteomas**, **epidermoid cysts**, and **desmoid tumors**. It is a variant of **familial adenomatous polyposis (FAP)** with extracolonic manifestations.

**Why the Correct Answer is Right**
The **exception** is likely an option claiming Gardner’s syndrome lacks extracolonic features (e.g., osteomas or epidermoid cysts). Gardner’s syndrome is distinguished from classic FAP by these **non-colonic abnormalities**, including **osteomas** (benign bone tumors), **retinal pigmented epitheliomas**, and **epidermoid cysts**. **APC gene mutations** drive the pathogenesis, leading to uncontrolled **Wnt/β-catenin signaling**, promoting colonic polyps and cancers.

**Why Each Wrong Option is Incorrect**
**Option A:** If stating Gardner’s is autosomal recessive—incorrect; it is **autosomal dominant**.
**Option B:** If claiming it

✓ Correct Answer: B. Always in 5th decade of life