**Core Concept**
The patient is likely suffering from hypertrophic cardiomyopathy (HCM), a condition characterized by abnormal thickening of the heart muscle, particularly the left ventricle. This thickening can lead to obstruction of blood flow and potentially life-threatening arrhythmias. The physical examination findings, including the murmur and ECG changes, are consistent with HCM.

**Why the Correct Answer is Right**
The correct answer is based on the high risk of sudden cardiac death associated with HCM. The patient's family history, with a first-degree relative dying suddenly at a young age, further increases the likelihood of HCM. The murmur that decreases with squatting and increases with standing is due to the dynamic left ventricular outflow tract obstruction, which worsens with increased preload and afterload. The ECG changes, including left ventricular hypertrophy, are also consistent with HCM.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the high risk of sudden cardiac death associated with HCM. While patients with HCM may be able to participate in low-intensity sports, the risk of sudden death remains a concern.

**Option B:** This option is incorrect because it does not take into account the family history of sudden cardiac death, which increases the likelihood of HCM.

**Option C:** This option is incorrect because it does not provide a clear recommendation regarding the patient's participation in sports.

**Option D:** This option is incorrect because it suggests that the patient can participate in high-intensity sports without any restrictions, which is not recommended for patients with HCM.

**Clinical Pearl / High-Yield Fact**
Patients with HCM should avoid strenuous physical activity, particularly high-intensity sports, due to the risk of sudden cardiac death. A thorough evaluation, including a family history, physical examination, ECG, and echocardiogram, is essential for diagnosing and managing HCM.

**Correct Answer: D. He should not participate in high-intensity sports.**