SCA17 (TBP) Genetic Testing (Repeat Expansion)

CPT: 81344

Expected Turnaround Time

2 - 4 weeks

Specimen Requirements


Whole blood


4 mL

Minimum Volume

1 mL


Lavender-top (EDTA) tube


Draw blood into EDTA tube.

Storage Instructions

Ship ASAP, but stable up to 5 days post-collection at room temperature. Do not freeze.

Stability Requirements



Room temperature

5 days


5 days


Do not freeze

Causes for Rejection

Frozen blood EDTA tube

Test Details


Spinocerebellar ataxias (SCAs), and episodic ataxias are the most common types of autosomal dominant cerebellar ataxias (ADCAs). SCAs are numbered based upon their time of identification. SCA3 is the most common type of SCA worldwide, followed by SCA2, SCA1, and SCA6. Some of the complicated forms have not been given a SCA number, like Dentatorubral Pallidoluysian Atrophy (DRPLA). Anticipation can be observed in the autosomal dominant ataxias in which CAG trinucleotide repeats occur. Anticipation results from expansion in the number of CAG repeats with transmission of the gene to subsequent generations. Most ADCAs have an overlap in clinical presentation, which makes it hard to differentiate. The most frequent clinical symptoms in all ADCAs are progressive adult-onset gait ataxia (often with hand dysmetria), and dysarthria associated with cerebellar atrophy. The episodic ataxias are characterized by periods of unsteady gait and often associated with nystagmus or dysarthria. Myokymia, vertigo, or hearing loss may occur in some of the subtypes. Permanent ataxia and even cerebellar atrophy may result late in the disease course.


Maximum reportable sizing: 120 repeats.

This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.


Repeat-Primed PCR (QP-PCR)

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