Spinocerebellar Ataxia Type 1 Expansion Analysis

Test Information

ATXN1 trinucleotide repeat analysis is a molecular test used to identify expanded CAG repeat size in the gene associated with spinocerebellar ataxia type 1.

Turnaround Time

21 days

CPT Code(s)

81178

Cost

$500

Genes

  • ATXN1

Clinical Information

Spinocerebellar ataxia type 1 is a progressive form of cerebellar ataxia with features that include lack of coordination and balance and dysarthria. Additional symptoms include vision problems such as nystagmus, dysphagia, hypotonia, peripheral neuropathy, and dysmetria. Bulbar signs such as facial muscle atrophy, difficulty chewing and swallowing, and perioral fasciculations may develop in the latter stages. Cognitive impairment may occur over time. Average age of onset is in the 20s-30s although childhood and late-adult onset have been reported. SCA1 is inherited in an autosomal dominant pattern, and it is caused by a CAG trinucleotide repeat expansion in the ATXN1 gene. One to three CAT interruptions are normally found within the CAG repeat stretch, and the presence of CAT interruptions helps to stabilize the repeat region. In the absence of CAT interruptions, the repeat region is less stable and susceptible to expansion. Repeat ranges are as follows: Normal (CAT absent 6-35; CAT present 6-44), Intermediate (CAT absent 36-38), Pathogenic (CAT absent ≥ 39; CAT present ≥ 45). Anticipation is more likely to occur with paternal transmission.

Methodology

Triplet repeat-primed PCR and restriction enzyme digest for determination of CAT interruption status

Detection

~100% for SCA1

Specimen Requirements

The preferred sample type is 3-5 ml of peripheral blood collected in an EDTA (purple top) tube. Extracted DNA and saliva are also accepted for this test. Saliva samples must be submitted in an approved saliva kit. Contact the lab to receive a saliva kit or to have one sent to your patient.

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

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