Friedreich ataxia (FRDA) is a member of the Repeat Expansion Diseases, a group of genetic conditions
resulting from an increase/expansion in the size of a specific tandem array. FRDA results from expansion
of a GAA/TTC-tract in the first intron of the frataxin gene (FXN). The disease-associated tandem repeats
all form secondary structures that are thought to contribute to the propensity of the repeat to expand.
The subset of these diseases that result from a CGG/CCG-repeat expansion, such as Fragile X syndrome,
also express a folate-sensitive fragile site coincident with the repeat on the affected chromosome. This
chromosome fragility involves the generation of chromosome/chromatid gaps or breaks, or the high
frequency loss of one or both copies of the affected gene when cells are grown under folate stress or as
we showed previously, in the presence of an inhibitor of the ATM checkpoint kinase. Whether Repeat
Expansion Disease loci containing different repeats form similar fragile sites was not known. We show
here that the region of chromosome 9 that contains the FXN locus is intrinsically prone to breakage
in vivo even in control cells. However, like FXS alleles, FRDA alleles show significantly elevated levels
of chromosome abnormalities in the presence of an ATM inhibitor, consistent with the formation of a
fragile site.
Published by Elsevier B.V
Friedreich ataxia (FRDA) is a member of the Repeat Expansion Diseases, a group of genetic conditionsresulting from an increase/expansion in the size of a specific tandem array. FRDA results from expansionof a GAA/TTC-tract in the first intron of the frataxin gene (FXN). The disease-associated tandem repeatsall form secondary structures that are thought to contribute to the propensity of the repeat to expand.The subset of these diseases that result from a CGG/CCG-repeat expansion, such as Fragile X syndrome,also express a folate-sensitive fragile site coincident with the repeat on the affected chromosome. Thischromosome fragility involves the generation of chromosome/chromatid gaps or breaks, or the highfrequency loss of one or both copies of the affected gene when cells are grown under folate stress or aswe showed previously, in the presence of an inhibitor of the ATM checkpoint kinase. Whether RepeatExpansion Disease loci containing different repeats form similar fragile sites was not known. We showhere that the region of chromosome 9 that contains the FXN locus is intrinsically prone to breakagein vivo even in control cells. However, like FXS alleles, FRDA alleles show significantly elevated levelsof chromosome abnormalities in the presence of an ATM inhibitor, consistent with the formation of afragile site.Published by Elsevier B.V
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