Spinal muscular atrophy (SMA) is a rare autosomal recessive disorder characterized by muscle atrophy and weakness resulting from motor neuron degeneration in the spinal cord and brainstem. It is most commonly caused by insufficient levels of survival motor neuron (SMN) protein (which is critical for motor neuron maintenance) secondary to deletions or mutations in the SMN1 gene. Nusinersen (SPINRAZA™) is a modified antisense oligonucleotide that binds to a specific sequence in the intron, downstream of exon 7 on the pre-messenger ribonucleic acid (pre-mRNA) of the SMN2 gene. This modulates the splicing of the SMN2 mRNA transcript to include exon 7, thereby increasing the production of full-length SMN protein. Nusinersen is approved in the USA for intrathecal use in paediatric and adult patients with SMA. Regulatory assessments for nusinersen as a treatment for SMA are underway in the EU and several other countries. This article summarizes the milestones in the development of nusinersen leading to this first approval for SMA in paediatric and adult patients.