How to Read a Friedreich Ataxia Genetic Test Report

When you look at a Friedreich ataxia genetic test report, the most important numbers you will see often correspond to your two copies (or alleles) of the FXN gene—one inherited from each parent ^[1]. These numbers measure the length of a repeating sequence of DNA called a GAA repeat.

Many labs label the shorter repeat as GAA1 and the longer one as GAA2, but naming conventions can vary, so always check how your specific laboratory defines them ^[1]. Doctors pay the most attention to the number for your shorter expanded allele (usually called GAA1). This is because the shorter expansion is less damaging to the gene’s ability to produce frataxin—the essential protein that is reduced in this condition ^[2]. Because it produces more frataxin than the longer allele, the shorter expansion is the primary genetic predictor of when symptoms might start ^[3].

Understanding Your GAA Repeat Numbers

Friedreich ataxia is caused by an abnormally long GAA section within the FXN gene ^[4]. In a typical report, your results will fall into categories based on the number of repeats. While exact cutoffs vary slightly among testing laboratories ^[5], they generally follow this pattern:

• Normal (usually 5 to 33 repeats): This does not cause the disease.
• Intermediate or Mutable Normal (usually 34 to 65 repeats): This does not cause symptoms, but the repeat could expand in future generations ^[6]. If you have this result, a genetic counselor can help explain what it means for family planning.
• Pathogenic or Expanded (66 or more repeats): This length can cause disease ^[4]. Commonly, these disease-causing expansions range from 600 to 1,200 repeats ^[4].

What Your Result May Mean

Friedreich ataxia is an autosomal recessive condition, meaning it typically requires a pathogenic change in both copies of the FXN gene to cause symptoms.

• Two Expanded Alleles: This is the most common cause of Friedreich ataxia and usually confirms the diagnosis ^[1].
• One Expanded Allele: This usually indicates you are a “carrier” who will not develop the disease. However, if you have symptoms of Friedreich ataxia, your doctor may order additional testing to look for a different kind of mutation—like a deletion (missing DNA) or a point mutation (a single letter change in the DNA)—on the other copy of the gene ^[7][8].
• No Expanded Alleles: This usually means you do not have Friedreich ataxia, but if symptoms strongly suggest it, further testing might be needed because standard repeat testing doesn’t look for other rare FXN mutations.

What the Repeat Number Can—and Cannot—Tell You

The length of your shorter expanded allele can provide a statistical baseline, but it is not a perfect predictor for your individual future ^[9].

• Age of Onset: At a population level, a longer shorter-allele expansion is strongly associated with an earlier age of symptom onset ^[3]. For example, one large study found that for every additional 100 repeats on the shorter allele, symptoms began about 2.3 years earlier on average ^[3]. Interestingly, this specific age-of-onset relationship seems to level off once the repeat number reaches about 700 ^[9].
• Other Complications: Longer repeat lengths have been associated in studies with lower frataxin levels and an increased likelihood of developing heart muscle disease (cardiomyopathy) and spine curvature (scoliosis) ^[2][9]. However, these are group-level trends. You must follow routine clinical monitoring guidelines for these complications regardless of your repeat size. A shorter repeat does not mean you can skip heart or spine checkups.
• Variation Between People: Even among siblings who share very similar repeat numbers, the age when symptoms start and the specific complications they develop can vary ^[10].
• Measurement Precision: Genetic tests cannot always count massive repeats with exact precision. Reports for very large expansions might include an estimated margin of error (for instance, ±50 repeats, though this depends entirely on the laboratory’s specific method) ^[6].
• Other Genetic Factors: Occasionally, specialized testing reveals uncommon variations, like non-GAA “interruptions” within the repeat sequence, which can sometimes result in milder symptoms than the repeat number alone would suggest ^[11].

Your doctor will use your genetic test alongside your physical symptoms and other medical evaluations to build a personalized care plan.