The present invention is directed to oligonucleotides based on peptide nucleic acid oligonucleotide or an equivalent oligonucleotide analogue, such as morpholino or a locked nucleic acid sequences and the use of such oligonucleotides for the dissociation of higher order structures, including triplex-helix DNA structures, in repeated sequences of DNA in Friedreichs ataxia. The dissociation of such structures may be used in the diagnosis and/or treatment of Friedreichs ataxia. Consequently, the present invention is also directed to a method for diagnosing Friedreichs ataxia and the use of peptide nucleic acid oligonucleotide or an equivalent oligonucleotide analogue, such as morpholino or a locked nucleic acid sequences in the treatment of Friedreichs ataxia. Preferably, the oligonucleotides comprise a sequence selected from the group consisting of (GAA)n, (CTT)n, (JTT)n or a mixed (JTT/CTT)n sequence.
