Spinocerebellar Ataxia Panel

General Information

Lab Name

Spinocerebellar Ataxia Panel

Lab Code

SCAPN

Epic Name

Spinocerebellar Ataxia Panel

Description

The dominant cerebellar ataxias are a clinically and genetically heterogeneous group of disorders that cannot be differentiated reliably from each other on a clinical basis. DNA testing is highly sensitive and specific and provides a definitive diagnosis for an estimated 50-60% of Caucasian patients with findings of dominant cerebellar ataxia. Patient DNA is analyzed to determine the number of CAG trinucleotide repeats located within each allele of the five causative genes; an abnormally large number of CAG repeats is diagnostic for the disease.

Two categories of tests are available:

• Spinocerebellar Ataxia Panel includes testing for all five types of SCA.
• Spinocerebellar Ataxia single test is offered to test for a single specific type: Spinocerebellar Ataxia 1 [SCA1T], Spinocerebellar Ataxia 2 [SCA2T], Spinocerebellar Ataxia 3 [SCA3T], Spinocerebellar Ataxia 6 [SCA6T], and Spinocerebellar Ataxia 7 [SCA7T].

Estimated Percent of Dominant Cerebellar Ataxias:

• Spinocerebellar Ataxia 1 (ATXN1) = 5-15%
• Spinocerebellar Ataxia 2 (ATXN2) = 10-15%
• Spinocerebellar Ataxia 3 (ATXN3) = 20-30%
• Spinocerebellar Ataxia 6 (CACNA1A) = 1-15%
• Spinocerebellar Ataxia 7 (ATXN7) = 1-5%

Notes:

• Frequencies of SCAs vary significantly in the Japanese and perhaps in other populations.
• Abnormal-sized ATXN7 alleles have been detected in ataxia patients without retinal degeneration.
• A DNA test for Friedreich ataxia, an autosomal recessive disorder, can be ordered separately (Online Test Guide Lab Mnemonic Friedreich's Ataxia DNA [FRDAX].

Indications for testing include:

• Symptomatic testing for patients with ataxia and a family history of ataxia
• Differential diagnosis for isolated cases of unexplained progressive ataxia (expect a relatively low positive rate)
• Presymptomatic testing for at-risk family members with appropriate genetic counseling

References

1. Schöls L, et al. Autosomal dominant cerebellar ataxia: phenotypic differences in genetically defined subtypes? Ann Neurol 1997, 42:924-32. 9403486
2. Goldfarb LG, et al. Unstable triplet repeat and phenotypic variability of spinocerebellar ataxia type 1. Ann Neurol 1996, 39:500-6. 8619528
3. Brandt V, Zoghbi HY. Spinocerebellar Ataxia Type 1. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997- . 1998 Oct 1 [updated 2017 Jun 22]. 20301363
4. Geschwind DH, Perlman S, Figueroa CP, Treiman LJ, and Pulst SM. The prevalence and wide clinical spectrum of the spinocerebellar ataxia type 2 trinucleotide repeat in patients with autosomal dominant cerebellar ataxia. Am J Hum Genet 1997, 60:842-50. 9106530
5. Pulst S-M. Spinocerebellar Ataxia Type 2. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997- . 1998 Oct 23 [updated 2019 Feb 14]. 20301452
6. Dürr A, et al. Spinocerebellar ataxia 3 and Machado-Joseph disease: clinical, molecular, and neuropathological features. Ann Neurol 1996, 39:490-9. 8619527
7. Paulson H. Spinocerebellar Ataxia Type 3. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997- . 1998 Oct 10 [updated 2015 Sep 24]. 20301375
8. Stevanin G, et al. Clinical and molecular features of spinocerebellar ataxia type 6. Neurology 1997, 49:1243-6. 9371901
9. Gomez CM. Spinocerebellar Ataxia Type 6. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-. 1998 Oct 23 [updated 2013 Jul 18]. 20301319
10. Giunti P, et al. Molecular and clinical study of 18 families with ADCA type II: evidence for genetic heterogeneity and de novo mutation. Am J Hum Genet 1999, 64:1594-603. 10330346
11. Garden G. Spinocerebellar Ataxia Type 7. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-. 1998 Aug 27 [updated 2012 Dec 20]. 20301433

Forms & Requisitions

Genetics Requisition

Synonyms

Ataxia Panel, MJD, SCA1, SCA2, SCA3, SCA6, SCA7

Components

Code	Name
SCA1A1	SCA1 ATXN1 Allele 1
SCA1A2	SCA1 ATXN1 Allele 2
SCA2A1	ATXN2 (SCA2), allele 1
SCA2A2	ATXN2 (SCA2), allele 2
SCA3A1	ATXN3 (SCA3), allele 1
SCA3A2	ATXN3 (SCA3), allele 2
SCA6A1	CACNA1A (SCA6), allele 1
SCA6A2	CACNA1A (SCA6), allele 2
SCA7A1	ATXN7 (SCA7), allele 1
SCA7A2	ATXN7 (SCA7), allele 2
SCAITP	SCA1 Interpretation
SCACOM	SCA1 Comment
SCAPDI	SCA Panel Director