In the present study, we add to our previous observations in the SMN-KO double transgenic mouse model (SMN2+/+; Smn−/−; SMN1A2G+/−) by characterizing at ultrastructural level, the peripheral muscular denervation which is supposed to occur early in neuromuscular disorders, including SMA. This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.