Importantly, injection of AAV9-p53shRNA but not AAV9-GFP strongly reduced nuclear p53 staining (Fig. 6G, H) and increased the number of PCs in lobules VI/VII of SMNΔ7 mice (Fig. 6G, I), demonstrating that p53 activation drives selective PC death in SMA mice. This evidence concerns the gene TP53 and proximal spinal muscular atrophy.