Table 1.

Molecular Genetic Testing Used in Spinocerebellar Ataxia Type 1

Gene 1MethodProportion of Pathogenic Variants 2 Detectable by Method
ATXN1 Targeted analysis for pathogenic variants 3, 4, 5100% 6
1.
2.

See Molecular Genetics for information on variants detected in this gene.

3.

Typically, the number of CAG repeats is determined by standard PCR and fragment length analysis.

4.

Distinguishing normal, mutable normal, and pathogenic alleles with 39-44 CAG repeats requires additional evaluation for the presence of CAT trinucleotides that interrupt the CAG repeat tract. Methods may vary (e.g., SfaNI restriction analysis [Chung et al 1993], dual-fluorescence labeled PCR-restriction fragment length analysis [Lin et al 2008], sequencing the PCR product of the CAG repeat region).

5.

In some individuals with infantile- or childhood-onset SCA1, direct amplification of the ATXN1 CAG repeat may not detect large repeat lengths in the hundreds. Southern blot analysis, long-range PCR, or CAG triplet repeat-primed PCR analysis can be used to quantify the CAG repeat number when infantile-onset SCA1 is suspected.

6.

Expansion of the number of CAG trinucleotide repeats in ATXN1 is the mutational mechanism in all individuals with SCA1 examined to date [Orr & Zoghbi 2001].

From: Spinocerebellar Ataxia Type 1

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