SMN2 and proximal spinal muscular atrophy: For this study, we used a milder SMA model (F0) (Smn–/– SMN2+/+) with 4 SMN2 copies obtained from Jackson Laboratory (JAX 005058) that are viable, are fertile, and have shortened, thick tails since severe SMA model mice have a median survival of only 8 days, making it difficult to evaluate the treatment efficacy when the BBB is mature.