Biology & Diagnosis: The Genetics of Friedreich Ataxia

At its core, Friedreich Ataxia (FRDA) is an “energy crisis” at the cellular level. While the symptoms affect the whole body, the cause is a very specific genetic error that prevents your cells from producing enough power to function correctly ^[1][2].

The Frataxin Energy Crisis

Every person has a gene called FXN, which provides the instructions for making a protein called frataxin ^[3]. Frataxin lives inside the mitochondria, the “power plants” of your cells. Its job is to help build iron-sulfur clusters, which are essential components for generating cellular energy (ATP) ^[3][4].

In FRDA, a genetic “stutter” interferes with this process:

1. The Stutter: In the FXN gene, a sequence of three DNA building blocks—G-A-A—repeats over and over. A healthy gene has about 5 to 33 of these GAA repeats ^[1].
2. The Intermediate Gap: People with 34 to about 100 repeats typically do not develop the typical disease. They may be asymptomatic carriers, or rarely, present with very mild, late-onset symptoms ^[1][5].
3. The Expansion: In people with FRDA, this section expands to hundreds or even over a thousand repeats. This extra DNA acts like a “stop” sign, silencing the gene ^[2][6].
4. The Deficiency: Because the gene is silenced, the body doesn’t make enough frataxin. Without it, iron builds up in the mitochondria, energy production drops, and cells become damaged by oxidative stress (a type of biological “rusting”) ^[7][8].

Your Genetic Report: A Completeness Checklist

A definitive diagnosis requires a molecular genetic test. Not all reports are equal; a complete report should provide specific details that help your medical team understand your unique situation ^[3][9].

Check your report for these three items:

• The Allele Count: You have two copies (alleles) of the FXN gene—one from each parent. The report should list the repeat length for both. These are often labeled GAA1 (the shorter one) and GAA2 (the longer one) ^[10].
• The Mutation Type:
  • Homozygous Expansion: About 96% of patients have GAA expansions on both alleles ^[1].
  • Compound Heterozygous: About 4% have a GAA expansion on one allele and a point mutation (a different kind of spelling error) on the other ^[11][5].
• Sequence Interruptions: Recent research shows that some GAA expansions are “interrupted” by other DNA sequences (like GAGG). These interruptions can sometimes lead to a later onset of symptoms ^[12][13].

“Look-Alike” Conditions (Differential Diagnosis)

Because the early symptoms of FRDA—like balance issues and scoliosis—can overlap with other conditions, doctors must rule out “look-alikes.” This process is called differential diagnosis ^[14]. Common conditions that can be confused with FRDA include:

• Ataxia with Vitamin E Deficiency (AVED): This condition looks almost identical to FRDA but is caused by the body’s inability to use Vitamin E. It is highly treatable with supplements, making it vital to rule out ^[14].
• Spinocerebellar Ataxias (SCAs): These are a large group of hereditary ataxias. While they share some symptoms, they usually have different genetic causes and progression patterns ^[15][16].
• Charcot-Marie-Tooth (CMT) Disease: A group of disorders that affect the peripheral nerves, which can cause similar walking and balance difficulties ^[14].

Understanding your specific genetic “signature” is the first step in moving from a general diagnosis to a personalized management plan. Use your genetic report as a tool to guide conversations with your neurology team ^[9].