Several findings suggest a potential implication of the Notch system in SMA pathology: Notch1 (hereafter referred to as Notch) as well as SMN share common functions in the regulation of neurite outgrowth [13,22–25], cell migration [26,27], axon guidance [28,29] and neuromuscular junction maturation [30,31]. Here, SMN1 is linked to proximal spinal muscular atrophy.