**Core Concept**
Zellweger syndrome is a rare genetic disorder characterized by the absence of functional peroxisomes in the liver, kidneys, and brain. Peroxisomes are organelles responsible for breaking down fatty acids and amino acids, and their dysfunction leads to the accumulation of very-long-chain fatty acids (VLCFAs) and other toxic compounds.

**Why the Correct Answer is Right**
The correct answer involves the absence of peroxisomes in Zellweger syndrome. Peroxisomes are essential for the breakdown of VLCFAs, which are crucial for energy production and membrane synthesis. The absence of peroxisomes leads to the accumulation of VLCFAs, resulting in a range of clinical symptoms, including developmental delay, seizures, and liver dysfunction. The impaired function of peroxisomes also affects the breakdown of amino acids, leading to the accumulation of pipecolic acid, a non-protein amino acid.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not directly relate to the pathophysiology of Zellweger syndrome. While mitochondria are also involved in energy production, the primary defect in Zellweger syndrome is the absence of peroxisomes.
* **Option B:** This option is incorrect because it refers to a different genetic disorder, not Zellweger syndrome. Mevalonate kinase deficiency is a disorder affecting cholesterol and isoprenoid metabolism, but it is not related to the absence of peroxisomes.
* **Option C:** This option is incorrect because it does not accurately describe the primary defect in Zellweger syndrome. While there is some overlap between peroxisomal and mitochondrial function, the primary defect in Zellweger syndrome is the absence of functional peroxisomes.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of Zellweger syndrome is the presence of a "classic triad" of clinical symptoms, including developmental delay, seizures, and liver dysfunction. Additionally, patients with Zellweger syndrome often exhibit a characteristic "dysmorphic" facial appearance, with features such as a high forehead, a prominent nose, and a thin upper lip.

**Correct Answer: C. Peroxisomes**