CRISPR/Cas9 targeted deletions in frataxin rescue Friedreich’s ataxia pathology in a human stem cell-based peripheral sensory neural circuitry

Friedreich's ataxia (FRDA) is an autosomal-recessive neurodegenerative and cardiac disorder which occurs when transcription of the FXN gene is silenced due to an excessive expansion of GAA repeats into its first intron. Herein, we generate dorsal root ganglia organoids (DRGOs) by in vitro differentiation of human iPSCs. Bulk and single-cell RNA sequencing show that DRGOs present a close transcriptional signature with native DRGs and display the main peripheral sensory neuronal and glial cell subtypes. Furthermore, when co-cultured with human intrafusal muscle fibers, DRGO sensory neurons contact their peripheral targets and reconstitute the muscle spindle proprioceptive receptors. FRDA DRGOs recapitulate key molecular and cellular deficits of the disease that are extensively rescued only when the entire FXN intron 1 is removed and not with the excision of merely the expanded GAA tract. These results strongly suggest that removal of the repressed chromatin flanking the GAA tract might be necessary to obtain a complete rescue of FXN expression and fully revert the pathological hallmarks of FRDA DRG neurons.