A 41-year-old woman has had diminished hearing for the past 4 months. On physical examination, she has decreased hearing on the left. Sound lateralizes to the right ear on the Weber tuning fork test. A head MRI shows a sharply circumscribed, 4-cm mass adjacent to the left pons that extends toward the left inferior cerebellar hemisphere. A smaller 1-cm lesion is in a similar location on the right. Family screening reveals a similarly affected 38-year-old sibling. An inherited mutation involving which of the following genes is most likely to be present in this patient?

**Core Concept**
The patient's presentation suggests a diagnosis of **neurofibromatosis type 2 (NF2)**, characterized by the development of **vestibular schwannomas** (also known as acoustic neuromas) on both sides. This condition is associated with an inherited mutation in a specific gene.

**Why the Correct Answer is Right**
The correct answer involves the **NF2 gene**, which encodes for the protein **merlin** (also known as **schwannomin**). This protein acts as a **tumor suppressor**, regulating cell growth and division. Mutations in the NF2 gene lead to the development of **benign tumors** in the nervous system, including vestibular schwannomas.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is associated with a different condition.
**Option B:** Incorrect as it is linked to another genetic disorder.
**Option C:** Incorrect because it is not related to the development of vestibular schwannomas.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **bilateral vestibular schwannomas** are a hallmark of **NF2**, distinguishing it from other conditions like **neurofibromatosis type 1 (NF1)**.

**Correct Answer:** **D. NF2**

✓ Correct Answer: A. NF2