SMN1 and proximal spinal muscular atrophy: To address the post-developmental roles of SMN deficiency in SMA pathogenesis, and to develop a mouse model for adult-onset SMA, we attempted to increase skipping of exon 7 in SMN2 transgene pre-mRNA in transgenic mice with four SMN2 copies (Smn−/−SMN2+/+) using ASOs.