**Core Concept**
Neurodegenerative disorders can be classified based on the specific populations of cells affected, including neurons, glial cells, and both neurons and glial cells. This question requires the student to identify a condition where neurons are exclusively affected.

**Why the Correct Answer is Right**
Guillain-Barré syndrome is an autoimmune disorder that primarily affects the myelin sheath of peripheral nerves, leading to demyelination. However, the condition where neurons are exclusively affected is Amyotrophic Lateral Sclerosis (ALS). In ALS, the degeneration of motor neurons is a hallmark of the disease, leading to progressive muscle weakness and atrophy. The selective vulnerability of motor neurons in ALS is due to the presence of toxic proteins such as SOD1 and TDP-43, which accumulate in the cytoplasm of motor neurons and cause their degeneration.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the question, as it does not mention a specific condition affecting neurons.
**Option B:** Multiple Sclerosis (MS) is an autoimmune disorder that affects the myelin sheath of both central and peripheral nerves, leading to demyelination. While MS primarily affects glial cells, it also affects neurons indirectly.
**Option C:** This option is not a specific medical condition and is therefore not relevant to the question.
**Option D:** This option is not relevant to the question, as it does not mention a specific condition affecting neurons.

**Clinical Pearl / High-Yield Fact**
The selective vulnerability of motor neurons in ALS is a key feature of the disease, and understanding the pathophysiology of ALS is crucial for developing effective treatments.

**Correct Answer:** C.