SMN2 and proximal spinal muscular atrophy: Treatment of type II SMA fibroblasts with MS023 led to a dose‐dependent increase in both SMN2 exon 7 inclusion and protein levels (Figs 2B–D and EV2A and Appendix Fig S1), and this effect was confirmed also in fibroblasts from severe (type I) and mild (type III) SMA patients (Fig EV2B and C).