SMN1 and proximal spinal muscular atrophy: Important insights into the spatial and temporal requirements of SMN, especially in the neuromuscular system, have been obtained by crossing existing SMA models with cell-type-specific or inducible-Cre mouse lines (Kariya et al., 2014; Kim et al., 2020; Lutz et al., 2011; Sleigh et al., 2011b).