CRISPR-Cas9-based therapies for Huntington's disease and Friedreich's ataxia: mechanisms, advances, and future perspectives.

Huntington's disease (HD) and Friedreich's ataxia (FRDA) are progressive inherited neurodegenerative disorders caused by trinucleotide repeat expansions but characterized by distinct pathogenic mechanisms. HD arises from a coding-region CAG expansion in the HTT gene that produces toxic gain-of-function effects of mutant huntingtin (mHTT), whereas FRDA results primarily from intronic GAA repeat expansion in FXN, leading to epigenetic repression and frataxin deficiency. The emergence of CRISPR-based genome engineering has created new opportunities to address these diseases at their genetic origin. This review examines current CRISPR therapeutic strategies for HD and FRDA, including allele-specific editing, transcriptional suppression, repeat excision, epigenetic reactivation, and emerging precision editing approaches such as base editing and prime editing. We compare the molecular rationale, preclinical outcomes, and translational limitations associated with each approach while highlighting how disease architecture influences therapeutic design. Although preclinical studies demonstrate promising restoration of cellular phenotypes and functional improvement, significant barriers remain. Efficient delivery to the central nervous system and cardiac tissue, control of editing duration, immune responses, off-target activity, and emerging concerns regarding on-target genomic instability continue to limit clinical translation. Recent advances in delivery engineering, non-viral systems, and programmable editing platforms suggest that future therapeutic success will depend on integrating disease-specific biology with increasingly precise and controllable genome engineering technologies. Ethical and regulatory concerns remain substantial, particularly regarding informed consent in the context of cognitive decline and the irreversibility of genomic modification.