SMN1 and proximal spinal muscular atrophy: Motor neurons from severe SMA transgenic mice manifested reduced axon elongation [59, 60], and specific FL-SMN silencing was related to evident reduction of neurite production and length of NSC-34 cells [61], to neurite degeneration of cultured mouse motor neurons [62] or reduced neurite outgrowth in motor neurons differentiated from embryonic stem cells [63].