SMN2 and proximal spinal muscular atrophy: As a follow-up study, Donadon et al. systemically delivered a U1 snRNA (ExSpeU1sma) specifically tailored to correct the SMN2 exon 7 splicing defect into the Taiwanese severe SMA mouse model (Smn−/−; SMN22TG/0) via two intraperitoneal (i.p.)injections of AAV9-ExspeU1sma (1.5 × 1012 vg per mouse) at P0 and P2.