SMN2 and proximal spinal muscular atrophy: The drugnusinersen (Spinraza®, Biogen, Cambridge, MA, USA) for the treatment of SMA is a 2′-O-methoxyethyl antisense oligonucleotide (AO) on a phosphorothioate backbone.Nusinersen targets a splice silencer (ISS-N1) in survival motor neuron 2 (SMN2) intron 7 and promotes exon 7 selection and retention during pre-mRNA splicing12 and was approved by the FDA in December 2016.