SMN2 and proximal spinal muscular atrophy: Furthermore, we showed that the disease phenotype observed in SMA MN cultures was rescued by the increase of SMN via oligonucleotides with morpholino (MO) chemistry targeting the ISS-N1 region of SMN2. We also tested the ability of an exon-specific U1 small nuclear RNA (ExSpeU1s) to rescue SMN2 pre-mRNA splicing.