**Core Concept**
Neurologic channelopathies refer to disorders caused by dysfunction or mutations in ion channels, which are vital for transmitting signals in neurons. These channelopathies can lead to various neurological symptoms and disorders. The most common types of ion channels involved in these conditions include voltage-gated sodium, potassium, and calcium channels.

**Why the Correct Answer is Right**
Huntington's disease is an autosomal dominant neurodegenerative disorder characterized by progressive motor dysfunction, cognitive decline, and psychiatric symptoms. It is caused by an expansion of CAG repeats in the Huntingtin gene, leading to a toxic protein that causes neuronal damage and death. Unlike other channelopathies, Huntington's disease does not result from mutations or dysfunction in ion channels. Instead, it is a proteinopathy, making it distinct from other channelopathies.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypokalemic periodic paralysis is a channelopathy caused by mutations in the calcium channel gene (CACNA1S) or the sodium channel gene (SCN4A), leading to episodes of muscle weakness and paralysis.
**Option B:** Episodic ataxias are a group of channelopathies that affect the P/Q-type calcium channel (CACNA1A) and the potassium channel (KCNQ2), causing brief episodes of ataxia and other neurological symptoms.
**Option C:** Familial hemiplegic migraine is a channelopathy caused by mutations in the sodium channel gene (SCN1A), calcium channel gene (CACNA1A), or potassium channel gene (KCNA1), leading to severe migraine attacks and hemiplegic episodes.

**Clinical Pearl / High-Yield Fact**
When evaluating patients with episodic neurological symptoms, consider channelopathies as a potential cause, especially if there is a family history of similar symptoms. Genetic testing can help identify the underlying cause and guide treatment.

**✓ Correct Answer: D. Huntington's disease**