title: Evidence for chromosome fragility at the frataxin locus in Friedreich ataxia.
abstract: 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.
authors.affiliation: Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Daman
authors.initials: D
authors.lastname: Kumari
authors.affiliation: Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Bruce
authors.initials: B
authors.lastname: Hayward
authors.affiliation: Laboratory of Molecular Pharmacology, CCR, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Asako J
authors.initials: AJ
authors.lastname: Nakamura
authors.affiliation: Laboratory of Molecular Pharmacology, CCR, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Bonner
authors.affiliation: Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA. Electronic address: ku@helix.nih.gov.
authors.forename: Karen
authors.initials: K
authors.lastname: Usdin
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D002873:Chromosome Fragility / Q000235:genetics*; D002899:Chromosomes, Human, Pair 9 / Q000235:genetics*; D005621:Friedreich Ataxia / Q000235:genetics*; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D033862:Iron-Binding Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D019680:Trinucleotide Repeat Expansion; D000096923:Frataxin
chemical_list: D033862:Iron-Binding Proteins; D000096923:Frataxin
keywords: Chromosome fragility; FXN; Frataxin; Friedreich ataxia; GAA/TTC-triplet repeat; Repeat expansion