SCA12 (PPP2R2B) Genetic Testing (Repeat Expansion)

Whole blood

Whole blood; oral swab or extracted DNA (from blood or oral swab only)

4 mL

Whole blood: 4 mL; oral swab: 3 swabs; or extracted DNA: contact MNG Genetic Services 844-664-8378 (844-MNGTEST)

Lavender-top (EDTA) tube

Whole blood: lavender-top (EDTA) tube; oral swab: OCD-100 DNA Genotek; or extracted DNA: contact MNG Genetic Services 844-664-8378 (844-MNGTEST)

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.

Diagnostic testing

Maximum reportable sizing: 150 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.

False positive or false negative results may occur for reasons that include insufficient information available about rare genetic variants, allele dropout, blood transfusions, bone marrow transplantation, somatic or tissue-specific mosaicism or mislabeled samples. Maximum reportable size of repeat expansion testing: ATN1: 110 repeats; ATXN1: 150 repeats (repeats greater than 40 in the ATXN1 gene cannot be assessed for CAT interruptions); ATXN2: 150 repeats; ATXN3: 120 repeats; ATXN7: 125 repeats; ATXN8/ATXN8OS: 150 repeats; ATXN10: 70 repeats; C9orf72: 65 repeats; CACNA1A: 145 repeats; CNBP: 373 base pairs (approximately 75 repeats); DMPK: 150 repeats; FXN: 1300 repeats; HTT: 100 repeats; JPH3: 100 repeats; NOP56: 65 repeats; PPP2R2B: 150 repeats; TBP: 120 repeats. Repeat sizes greater than the maximum reportable range are reported as greater than the largest reportable repeat size.

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)

Repeat-primed PCR and fragment length analysis to identify number of nucleotide repeats