## **Core Concept**
Friedreich's ataxia is a genetic disorder caused by an expansion of a GAA trinucleotide repeat within the *FXN* gene, which encodes frataxin. This disorder leads to progressive damage to the nervous system and other tissues. The *FXN* gene is located on chromosome 9.

## **Why the Correct Answer is Right**
The correct answer involves the expansion of GAA triplet repeats in the *FXN* gene. This expansion leads to reduced expression of frataxin, a mitochondrial protein crucial for iron homeostasis and oxidative stress protection. The deficiency of frataxin disrupts mitochondrial function, particularly in cells with high energy demands like neurons and cardiomyocytes.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify the correct gene or type of repeat associated with Friedreich's ataxia.
- **Option B:** This option is incorrect as it refers to another condition, not Friedreich's ataxia.
- **Option D:** This option is incorrect because it also refers to a different condition, not related to the GAA repeats in the *FXN* gene.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Friedreich's ataxia is the most common inherited ataxia and typically presents in childhood or adolescence with progressive ataxia, dysarthria, and loss of reflexes. Early diagnosis through genetic testing can help in managing symptoms and providing genetic counseling.

## **Correct Answer:** . GAA