While the levels of Klf15 expression achieved with AAV8-Klf15 are similar to the levels observed in transgenic SMA mice overexpressing muscle-specific Klf15 at P2 (~5–10 fold greater than control littermates), the amounts measured in P7 AAV8-Klf15-treated animals are significantly greater than the transgenic mice (~65–740 fold greater and ~30 fold greater, respectively, compared with control littermates) (Fig. 2) [18]. This evidence concerns the gene KLF15 and proximal spinal muscular atrophy.