**Core Concept**
A high intake of certain amino acids has been linked to an increased risk of coronary heart disease (CHD) due to their effects on lipid metabolism and atherogenesis. The specific amino acid in question plays a crucial role in the regulation of cholesterol synthesis and transport in the body.

**Why the Correct Answer is Right**
The amino acid in question, **lysine**, has been shown to have a high risk for CHD due to its role in inhibiting the activity of **HMG-CoA reductase**, a key enzyme involved in cholesterol synthesis. This inhibition leads to a decrease in the production of cholesterol in the liver, which in turn can increase the levels of low-density lipoprotein (LDL) cholesterol, a major risk factor for CHD. Additionally, lysine has been found to increase the levels of apolipoprotein B, a protein component of LDL cholesterol.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not have a direct impact on cholesterol synthesis or transport.
* **Option B:** This option is incorrect because it actually has a protective effect against CHD by reducing the levels of LDL cholesterol.
* **Option D:** This option is incorrect because it is not directly related to the regulation of cholesterol synthesis or transport in the body.

**Clinical Pearl / High-Yield Fact**
It is essential to note that a high intake of lysine can have a negative impact on cardiovascular health, and individuals with a history of CHD or at risk for the disease should limit their consumption of this amino acid.

**Correct Answer: C. Lysine**