Spinocerebellar Ataxia Type 3 Repeat Analysis
Use
This test evaluates for CAG trinucleotide repeat expansion in the ATXN3 gene, causative of Machado‑Joseph disease (spinocerebellar ataxia type 3). The size of the repeat correlates with disease penetrance and onset; expansions of 60 or more repeats are fully penetrant, while 45–59 repeats show intermediate penetrance; repeats ≤44 are generally benign. The test aids in diagnostic confirmation in individuals with clinical signs or family history of SCA3.
Special Instructions
Orderable via GeneDx’s Neurology Test Requisition form (TH86). The test is part of GeneDx’s repeat expansion analysis menu for spinocerebellar ataxia, allowing single‑gene analysis for ATXN3 as an alternative to the expanded panel. Specific collection and consent requirements (e.g., New York) should be referred to the requisition and test menu guidance.
Limitations
The assay detects only repeat expansions within ATXN3; it does not assess other variant types or repeat expansions beyond assay limits. Repeat sizing accuracy is ±2 repeats for ≤50 repeats, ±5 repeats for 51–100 repeats, and exact sizing for expansions >100 repeats is not possible without Southern blot, which is not included. Southern blot may be required for very large expansions.
Methodology
PCR-based (PCR)
Biomarkers
Result Turnaround Time
Not provided.
Related Documents
For more information, please review the documents below
Specimen
Whole Blood
Volume
Not provided
Minimum Volume
Not provided