**Core Concept**
Hyperophic Obstructive cardiomyopathy (HOCM) is a genetic disorder characterized by abnormal thickening of the myocardium, particularly the left ventricular septum. This thickening can lead to obstruction of the left ventricular outflow tract (LVOT), resulting in symptoms of heart failure and arrhythmias.

**Why the Correct Answer is Right**
The thickening of the myocardium in HOCM is primarily due to mutations in genes encoding sarcomeric proteins, such as myosin heavy chain (MYH7) and cardiac troponin T (TNNT2). These mutations lead to an increase in the contractile force of the heart muscle, causing the septum to thicken and the LVOT to narrow. The pathophysiology of HOCM is further complicated by the presence of dynamic LVOT obstruction, which can be exacerbated by factors such as exercise or emotional stress.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because HOCM is not typically associated with a dilated left ventricle. In fact, the left ventricle is often small and hypertrophied in HOCM.
**Option B:** This option is incorrect because HOCM is not a primary cause of cardiac arrhythmias due to electrolyte imbalances. While arrhythmias can occur in HOCM, they are more likely related to the underlying structural abnormalities of the heart.
**Option C:** This option is incorrect because HOCM is not typically associated with a significant increase in left ventricular end-diastolic volume (LVEDV). In fact, LVEDV is often decreased in HOCM due to the hypertrophied septum.

**Clinical Pearl / High-Yield Fact**
One key clinical feature of HOCM is the presence of a "systolic murmur" that is typically grade 3/6 or greater in intensity. This murmur is often heard best at the right upper sternal border and is associated with a "click" or "double apex" in some patients.

**Correct Answer: D.**