SMN2 and proximal spinal muscular atrophy: Indeed increasing evidence suggest that SMA pathogenesis is more complex than expected: many authors have recently speculated that, even though MNs are the most affected cells in SMA, their loss might not only depend from the lack of SMN: retrograde signals coming from muscles and NMJs can be crucial players of the MN alteration (Bottai and Adami, 2013).