MSTN and proximal spinal muscular atrophy: Previous studies have suggested that suppression of the myostatin pathway has only limited therapeutic benefit in the severe SMNΔ7 mice.31, 32, 33 To determine the baseline effect of AAV‐MPRO in SMA mice, we injected AAV‐MPRO (2.5 × 1010 vp) subcutaneously in the severe Taiwanese SMA mice at PND 0.