Nusinersen, the first approved therapy for SMA, is an antisense oligonucleotide (ASO) that restores SMN2 exon 7 inclusion upon binding to the intronic splicing silencer N1 (ISS-N1) located immediately downstream of the 5′ splice site (5′ss) of exon 7 (11,12). The gene discussed is SMN2; the disease is proximal spinal muscular atrophy.