**Core Concept**
Refsum disease is a rare genetic disorder characterized by the accumulation of a specific type of fatty acid called phytanic acid in the body. This accumulation leads to a range of clinical and biochemical abnormalities.

**Why the Correct Answer is Right**
Refsum disease is caused by mutations in the alpha-oxidase enzyme, which is responsible for breaking down phytanic acid. The accumulation of phytanic acid disrupts the normal functioning of the nervous system, leading to symptoms such as peripheral neuropathy, visual impairment, and ataxia. The disease is typically diagnosed through a combination of clinical evaluation, laboratory tests, and genetic analysis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a feature of Refsum disease. However, Refsum disease can present with similar symptoms to other neurological disorders, making diagnosis challenging.
**Option B:** This option is incorrect because it is actually a characteristic of Refsum disease. Phytanic acid accumulation is a hallmark of the disease.
**Option C:** This option is incorrect because it is not a specific feature of Refsum disease. While some patients may experience developmental delays, it is not a universal characteristic of the disease.

**Clinical Pearl / High-Yield Fact**
One key feature of Refsum disease is the presence of retinitis pigmentosa, a condition characterized by progressive vision loss and night blindness. This is due to the accumulation of phytanic acid in the retina.

**Correct Answer: B. Phytanic acid accumulation.**