**Core Concept**
Hyperophic cardiomyopathy (HCM) is a genetic disorder characterized by an abnormal thickening of the heart muscle, leading to impaired cardiac function and increased risk of sudden cardiac death. This thickening is usually asymptomatic and can affect any of the three layers of the heart muscle.

**Why the Correct Answer is Right**
HCM is often caused by mutations in genes encoding sarcomeric proteins, which are essential for the contraction and relaxation of heart muscle cells. The thickened heart muscle can lead to obstruction of blood flow out of the heart, particularly during exercise, and can also increase the risk of arrhythmias due to abnormal electrical conduction through the heart.

**Why Each Wrong Option is Incorrect**
**Option A:** HCM is indeed characterized by a left ventricular wall thickness of 15 mm or greater, which is a diagnostic criterion.
**Option B:** Sudden cardiac death is a well-known complication of HCM, particularly in young athletes.
**Option C:** The risk of sudden cardiac death in HCM is highest during physical exertion or emotional stress.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of HCM is the presence of a late systolic murmur best heard at the left sternal border, which is due to the obstruction of blood flow out of the left ventricle.

**Correct Answer:**
(Insert the actual question options and the correct letter here to complete the explanation)