Epigenetic reactivation in Friedreich's ataxia from benzamides to gene‑targeted chimeras

Friedreich's ataxia (FRDA) is a prototypical repeat expansion disorder in which large intronic guanine‑adenine‑adenine (GAA) tracts at the frataxin (FXN) gene locus induce heterochromatin formation, impaired transcriptional elongation, and reduced FXN expression, driving progressive neurodegeneration and cardiomyopathy. Epigenetic therapies that restore endogenous FXN transcription have therefore emerged as a coherent disease‑modifying strategy focused on reversing repeat‑associated gene silencing at its root.

This review summarizes the evolution of FXN protein‑reactivating approaches from first‑generation systemic epigenetic therapies, including class I‑selective benzamide histone deacetylase inhibitors and high‑dose nicotinamide, to emerging locus‑targeted platforms such as anti‑gene oligonucleotides and gene‑targeted chimera small molecules. The authors also examine splice‑modulating strategies aimed at increasing the extra‑mitochondrial FXN‑E isoform, discuss delivery and safety challenges across modalities, and highlight biomarker frameworks integrating isoform‑resolved FXN protein measurements and chromatin readouts. PubMed/MEDLINE, Embase, Web of Science, Google Scholar, and Cochrane Library for trial reports were searched from January 1996 to June 2026.

Early clinical programs established that FXN protein expression and chromatin marks can be pharmacologically modulated in humans, but also exposed the limitations of non‑selective chromatin modulation for chronic pediatric‑onset neurodegeneration. In our view, the most promising path forward lies in repeat‑ and locus‑directed FXN reactivation, complemented by splicing‑directed modulation of FXN‑E, with rigorous attention to CNS and cardiac exposure, off‑target risk, and mechanistically anchored biomarkers.