Protein affected in spinocerebellar ataxia type 6
**Core Concept**
The **spinocerebellar ataxias (SCAs)** are a group of autosomal dominant disorders characterized by progressive cerebellar degeneration, leading to ataxia. **Spinocerebellar ataxia type 6 (SCA6)** is caused by mutations in a specific gene.
**Why the Correct Answer is Right**
SCA6 is caused by an expansion of **CAG repeats** in the **CACNA1A gene**, which encodes the **alpha1A subunit of the P/Q-type calcium channel**. This mutation leads to a toxic gain of function, disrupting calcium homeostasis and ultimately causing neuronal degeneration.
**Why Each Wrong Option is Incorrect**
**Option A:** Not related to SCA6.
**Option B:** Not related to SCA6.
**Option D:** Not related to SCA6.
**Clinical Pearl / High-Yield Fact**
SCA6 is notable for its relatively late onset and slow progression, often presenting in the fifth or sixth decade of life.
**Correct Answer:** C. CACNA1A gene