SMN2 and proximal spinal muscular atrophy: Nusinersen/ASO10-27/SPINRAZA, an approved antisense oligonucleotide (ASO) drug for the treatment of SMA, directly targets intronic splicing silencer N1 (ISS-N1) in intron 7 of SMN26,7, which modulates SMN2 splicing, and leads to an increase in SMN protein levels8.