Here, we describe an approach to correct the genetic defect in fragile X syndrome (FXS) via recruitment of endogenous repair mechanisms. A leading cause of autism spectrum disorders, FXS results from epigenetic silencing of FMR1 due to a congenital trinucleotide (CGG) repeat expansion. By investigating conditions favorable to FMR1 reactivation, we find MEK and BRAF inhibitors that induce a strong repeat contraction and full FMR1 reactivation in cellular models. We trace the mechanism to DNA demethylation and site-specific R-loops, which are necessary and sufficient for repeat contraction. A positive feedback cycle comprising demethylation, de novo FMR1 transcription, and R-loop formation results in the recruitment of endogenous DNA repair mechanisms that then drive excision of the long CGG repeat. Repeat contraction is specific to FMR1 and restores the production of FMRP protein. Our study therefore identifies a potential method of treating FXS in the future.

在这里，我们描述了一种通过招募内源性修复机制来纠正脆性 X 综合征 (FXS) 遗传缺陷的方法。FXS 是自闭症谱系障碍的主要原因，是由于先天性三核苷酸 (CGG) 重复扩增导致FMR1表观遗传沉默的结果。通过研究有利于FMR1重新激活的条件，我们发现 MEK 和 BRAF 抑制剂可在细胞模型中诱导强烈的重复收缩和完全FMR1重新激活。我们追踪 DNA 去甲基化和位点特异性 R 环的机制，这对于重复收缩是必要且充分的。包括去甲基化、从头 FMR1转录和 R 环形成的正反馈循环导致内源 DNA 修复机制的募集，然后驱动长 CGG 重复的切除。重复收缩是FMR1特有的，可恢复 FMRP 蛋白的产生。因此，我们的研究确定了未来治疗 FXS 的潜在方法。