SCA Gene Test

Norm of SCA Gene Test

Normal repeat numbers range from 15 to 29.
Cytosine Adenosine Guanine Repeat Range


Normal 6–39 14–31 12–41 7–18 7–17 Not found
Pathologic 41–81 35–64 40–84 21–27 38–130 Not found


Usage of SCA Gene Test

Genetic testing determines diagnosis, course of disease, and likelihood of transmission of disease from generation to generation.


Description of SCA Gene Test

SCA gene testing identifies autosomal dominant neurodegenerative spinocerebellar ataxia (SCA) genes found in Machado-Joseph disease (MJD) and other ataxias. SCA1, SCA2, SCA3, SCA6, SCA7, and SCA12 are members of a group known as “triplet repeat diseases” or “CAG repeat diseases” (cytosine, adenine, and guanine). In CAG repeat diseases, the trinucleotide sequence repeats abnormally within the gene coding sequence. At least 8 genes have been identified as causative for the cerebellar ataxias. MJD, one of the most common ataxias, is characterized by abnormalities in the SCA3 gene. It includes symptoms of progressive weakness of the extremities, spasticity, dysphagia, exophthalmos, diplopia, and urinary frequency, and can occur in either mild or severe form, beginning at age 10 years. By identification of the intricate intracellular mechanisms by which SCA functions, treatments and cures for neurodegenerative diseases may eventually be found. This test involves isolating the DNA from the blood sample and then amplifying the CAG repetitions via polymerase chain reaction.


Professional Considerations of SCA Gene Test

Consent form IS required.

  1. Tube: Lavender topped.



  1. Collect a 3.5-mL blood sample. Lavender-topped tubes need 10–20 mL of whole blood.


Postprocedure Care

  1. None.


Client and Family Teaching

  1. Consult insurance provider or legal counsel before having test done.
  2. Persons with the disease had numbers from 35 to 59.
  3. A repeat number in the low fifties for SCA2 probably represents a severe form of the disease.


Factors That Affect Results

  1. Less than 3 mL in EDTA tube.
  2. SCA diseases vary considerably across different ethnic groups and geographic regions.


Other Data

  1. None.