SMN1 and proximal spinal muscular atrophy: This approach to SMA has been successful in that there are currently 3 therapies–nusinersen (4, 5), risdiplam (6) and onasemnogene abeparvovec (7)–that are approved for clinical use which target SMN expression, either by SMN1 gene replacement or modulating the alternative splicing of the orthologous SMN2 gene.