SMN1 and proximal spinal muscular atrophy: SpCas9 mRNA and sgRNA1 targeting ISS-N1, the most commontarget for treating SMA [31], were co-injectedinto the cytoplasm of zygotes (harvested from heterozygous BH mice(Smn+/−) that had been previously mated with type III HFmice (Smn−/−; SMN2tg/tg)) (Fig.2A).