**Core Concept**
Gardner syndrome is a variant of familial adenomatous polyposis (FAP), characterized by the presence of multiple colorectal adenomatous polyps and extracolonic manifestations such as osteomas, skin and soft tissue tumors, and dental anomalies. It is an autosomal dominant disorder.

**Why the Correct Answer is Right**
Gardner syndrome is caused by mutations in the APC gene, which is a tumor suppressor gene that regulates cell growth and division. The APC gene is located on chromosome 5q21-22 and encodes a protein that binds to beta-catenin, preventing its accumulation in the nucleus and subsequent activation of the Wnt/beta-catenin signaling pathway. When the APC gene is mutated, beta-catenin accumulates and activates the Wnt/beta-catenin pathway, leading to uncontrolled cell growth and tumor formation.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because Gardner syndrome is not caused by mutations in the MYC gene, which is a proto-oncogene involved in cell proliferation and apoptosis.

**Option B:**
This option is incorrect because Gardner syndrome is not an autosomal recessive disorder; it is an autosomal dominant disorder, meaning that a single copy of the mutated APC gene is sufficient to cause the condition.

**Option C:**
This option is incorrect because Gardner syndrome is not caused by mutations in the TP53 gene, which is a tumor suppressor gene involved in cell cycle regulation and DNA repair.

**Clinical Pearl / High-Yield Fact**
The APC gene is one of the most commonly mutated genes in human cancer, and mutations in this gene are associated with a high risk of developing colorectal cancer.

**Correct Answer: C. Autosomal dominant.**