The first approved drug for SMA was nusinersen, which is an ASO that promotes the inclusion of exon 7 in mRNA transcripts of SMN2. Nusinersen binds to an intronic splice-silencing-site in intron 7 of SMN2 and inhibits the action of other splice-factors, promoting exon 7 incorporation into the mRNA. Here, SMN2 is linked to proximal spinal muscular atrophy.