Spinocerebellar Ataxia Type 3 Expansion Analysis

Test Information

ATXN3 trinucleotide repeat analysis is a molecular test used to identify expanded CAG repeat size in the gene associated with spinocerebellar ataxia type 3.

Turnaround Time

21 days

CPT Code(s)





  • ATXN3

Clinical Information

Spinocerebellar ataxia type 3, also known as Machado-Joseph disease, is the most common form of hereditary spinocerebellar ataxia . Features include lack of coordination and balance, gait abnormalities, vision problems such as nystagmus and ophthalmoplegia, dysphagia, and dysarthria. Parkinsonism develops over time including spasticity, rigidity, dystonia, and tremor. Peripheral neuropathy, muscle weakness, and fasciculations may occur. Average age of onset ranges form the teens to the 40s, and lifespan is typically reduced. SCA3 is inherited in an autosomal dominant pattern, and it is caused by a CAG trinucleotide repeat expansion in the ATXN3 gene. Repeat ranges are as follows: Normal (≤ 44), Intermediate (45-59), Pathogenic (≥ 60). Intermediate alleles may have incomplete penetrance, and the age of onset and rate of progression correlate with the size of the expansion.


Triplet repeat-primed PCR


~100% for SCA3

Specimen Requirements

The preferred sample type is peripheral blood collected in an EDTA (purple top) tube - at least 2-3ml for pediatric patients and 5-6ml for adult patients. Saliva is also accepted.

Transport Instructions

The specimen should be kept at room temperature and delivered via overnight shipping. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Do not freeze the specimen. Samples collected on Friday can be safely designated for Monday delivery.

Prenatal Testing Information

Prenatal testing may be available in cases where one parent is known to have an expanded allele. Please contact the lab to discuss specific cases prior to sending a sample.

Have Questions? Need Support?

Call our laboratory at 1-800-473-9411 or contact one of our Laboratory Genetic Counselors for assistance.
Robin Fletcher, MS, CGC
Falecia Thomas, MS, CGC

One Mother's Story

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