**Core Concept**
The most likely diagnosis is Multiple Endocrine Neoplasia Type III (MEN III), a rare autosomal dominant disorder characterized by medullary thyroid carcinoma, pheochromocytoma, and mucosal neuromas, with no parathyroid involvement. It results from mutations in the **RET proto-oncogene**, though with a distinct pattern compared to other MEN syndromes.

**Why the Correct Answer is Right**
MEN III is caused by **RET gene mutations** and presents with **medullary thyroid carcinoma**, **pheochromocytoma**, and **mucosal neuromas** (especially in the oral and gastrointestinal tracts). Unlike MEN I or II, it does **not** involve parathyroid glands. The syndrome is typically associated with **late-onset** disease and is linked to **neuroendocrine tumors** arising from neural crest cells. The presence of all three features—medullary thyroid cancer, pheochromocytoma, and mucosal neuromas—without parathyroid involvement is highly specific for MEN III.

**Why Each Wrong Option is Incorrect**
Option A: MEN Type I involves **parathyroid adenomas**, **pituitary adenomas**, and **medullary thyroid carcinoma**—but **not mucosal neuromas**. Also, pheochromocytoma is rare in MEN I.
Option B: MEN Type II includes **medullary thyroid carcinoma**, **pheochromocytoma**, and **parathyroid adenomas** (in some variants), but **mucosal neuromas are absent**. It also occurs in early life and is associated with **MEN II-A and II-B**.
Option D: Sipple’s syndrome (also known as Multiple Endocrine Neoplasia Type II, or MEN II with syndromic features) includes **medullary thyroid cancer**, **pheochromocytoma**, and **mucosal neuromas**, but **parathyroid involvement is common**—contrary to the patient’s presentation.

**Clinical Pearl / High-Yield Fact**
MEN III is rare and primarily presents with **neuroendocrine tumors** without parathyroid involvement. It is often **diagnosed late** due to subtle symptoms and is linked to **RET gene mutations**—but unlike MEN I/II, it lacks parathyroid disease.

✓ Correct Answer: C. MEN type III