Spinocerebellar Ataxia Type 7 Expansion Analysis

Clinical Information

Spinocerebellar Ataxia Type 7 (SCA7) is a progressive form of cerebellar ataxia with features including dysarthria and dysphagia, and cone-rod dystrophy with progressive central visual loss resulting in blindness. SCA7 is inherited in an autosomal dominant pattern, and it caused by a CAG trinucleotide repeat expansion in the ATXN7 gene. Repeat ranges are as follows: normal (≤ 27), intermediate (28-33), reduced penetrance (34-36), and pathogenic (≥ 37).

Technical Information

• This test is performed using triplet repeat-primed PCR.
• Genomic DNA is analyzed for trinucleotide (CAG) repeat expansion in the ATXN7 gene. The triplet repeat-primed polymerase chain reaction (TP-PCR) assay used for analysis is based on a method described by Cagnoli et al. (J Mol Diagn. 2018 May;20(3):289-297).
• The number of trinucleotide repeats in the ATXN7 gene is briefly analyzed using TP-PCR and capillary electrophoresis followed by data analysis using GeneMarker software.

Specimen Requirements

• The preferred sample type is 3-4 ml of peripheral blood collected in an EDTA (purple top) tube. Extracted DNA and saliva are also accepted for this test. Blood and saliva kits are available by request.
• Send approximately 5µg of extracted DNA at a requested concentration of 90-130 ng/µl.
• Saliva samples must be submitted in an approved saliva kit, and sample kits are available upon provider request.

Transport Instructions

• The blood 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.
• Extracted DNA should be sent at room temperature via overnight delivery.
• Saliva is stable at room temperature and can be delivered via overnight or ground shipping.