Spinal muscular atrophy (SMA) is caused by mutations in SMN1. SMN2 is a paralogous gene with a C•G-to-T•A transition in exon 7, which causes this exon to be skipped in most SMN2 transcripts, and results in low levels of the protein survival motor neuron (SMN). Here we show, in fibroblasts derived from patients with SMA and in a mouse model of SMA that, irrespective of the mutations in SMN1, adenosine base editors can be optimized to target the SMN2 exon-7 mutation or nearby regulatory elements to restore the normal expression of SMN. After optimizing and testing more than 100 guide RNAs and base editors, and leveraging Cas9 variants with high editing fidelity that are tolerant of different protospacer-adjacent motifs, we achieved the reversion of the exon-7 mutation via an A•T-to-G•C edit in up to 99% of fibroblasts, with concomitant increases in the levels of the SMN2 exon-7 transcript and of SMN. Targeting the SMN2 exon-7 mutation via base editing or other CRISPR-based methods may provide long-lasting outcomes to patients with SMA.

脊髓性肌萎缩症 (SMA) 是由SMN1突变引起的。SMN2是一个旁系同源基因，在外显子 7 中具有 C•G 到 T•A 转变，这导致该外显子在大多数SMN2转录本中被跳过，并导致运动神经元 (SMN) 蛋白存活率较低。在这里，我们表明，在来自 SMA 患者的成纤维细胞和 SMA 小鼠模型中，无论SMN1突变如何，腺苷碱基编辑器都可以优化以靶向SMN2外显子 7 突变或附近的调控元件，以恢复正常表达的SMN。在优化和测试了 100 多个向导 RNA 和碱基编辑器，并利用具有高编辑保真度且能够耐受不同原型间隔子相邻基序的 Cas9 变体后，我们通过 A·T 到 G 实现了外显子 7 突变的逆转• 高达 99% 的成纤维细胞中的 C 编辑，伴随着SMN2外显子 7 转录物和 SMN水平的增加。通过碱基编辑或其他基于 CRISPR 的方法靶向SMN2外显子 7 突变可能为 SMA 患者提供持久的结果。