Antisense oligonucleotide therapy for patients with Friedreich's ataxia carrying the c.165+5G>C splicing mutation

Friedreich's ataxia (FRDA) is a multisystem, progressive disease. 96% of patients carry biallelic GAA triplet expansion mutations in intron 1 of the frataxin gene (FXN). The remaining 4% have a pathogenic GAA expansion on one FXN allele and another mutation on the second allele. A point mutation, FXN c.165+5G>C, was identified in intron 1 of a patient with FRDA resulting in a significant decrease of FXN levels. Using patient fibroblasts, we demonstrated that the c.165+5G>C mutation affects canonical splicing of FXN, leading to the generation of an aberrant transcript. A library of antisense oligonucleotides (ASOs) was designed to target potential intronic splicing regulator motifs and tested in patient cells. Selected O-methoxyethyl (MOE)-ASOs increased FXN levels in c.165+5G>C patient cells without affecting FXN splicing in control cells. The leading MOE-ASO increased expression of a miniFXN gene carrying the c.165+5G>C point mutation by splicing repair. To increase efficacy, we simultaneously targeted the GAA-expanded allele in patient cells using a synthetic transcription factor (synthetic transcription elongation factor 1 [Syn-TEF1]). This ASO strategy may be therapeutically feasible for patients with FRDA with other point mutations that cause splicing defects. Success in developing treatments for disorders with only a few known cases will give hope to patients with FRDA carrying these rare point mutations.