Overall, these findings reinforce the view that SMN is not the only target in SMA, and that despite multiple roles of SMN and its involvement in a plethora of cellular pathways, it is dispensable and replaceable in most of them, except for motor neuron-specific, such as, signal transduction at neuro-muscular junctions via secretory vesicle signaling. Here, SMN1 is linked to proximal spinal muscular atrophy.