SMN2 and proximal spinal muscular atrophy: In contrast, less than 10% of SMN2 transcripts are FL, and more than 90% lack exon 7 (Δ7).5 In SMA, the low levels of FL-SMN protein generated from SMN2 may partially compensate for the lack of SMN1. Progress in our understanding of SMN splicing mechanisms has spurred the development of therapeutic compounds that modify the splicing of SMN2 exon 7 to increase levels of FL-SMN protein, and several SMA clinical trials with such therapeutic compounds, including ISIS-SMNRx (nusinersen) and RG7800, are currently in progress.6