Table 1.

Molecular Genetic Testing Used in Friedreich Ataxia

Gene 1MethodProportion of Pathogenic Variants 2 Identified by Method
FXN Targeted analysis for GAA repeat expansion 396%
Sequence analysis for sequence variants 4 or CNV analysis for a large FXN intragenic or whole-gene deletion 54%
1.

See Table A. Genes and Databases for chromosome locus and protein.

2.

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

3.

Sequence-based multigene panels and exome sequencing cannot reliably detect pathogenic repeat expansions in this gene. However, pathogenic repeat expansions may be more reliably detected using customized tools and long-read sequencing.

4.

Sequence analysis detects variants that are benign, likely benign, of uncertain significance, likely pathogenic, or pathogenic. Variants may include missense, nonsense, and splice site variants and small intragenic deletions/insertions; typically, exon or whole-gene deletions/duplications are not detected. For issues to consider in interpretation of sequence analysis results, click here.

5.

Gene-targeted deletion/duplication analysis detects intragenic deletions or duplications. Methods used may include a range of techniques such as quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and a gene-targeted microarray designed to detect single-exon deletions or duplications. Exome and genome sequencing may be able to detect deletions/duplications using breakpoint detection or read depth; however, sensitivity can be lower than gene-targeted deletion/duplication analysis.

From: Friedreich Ataxia

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