SMN2 and proximal spinal muscular atrophy: Even if the genetic causes of SMA are well known, many aspects of its pathogenesis remain unclear and only three drugs have been recently approved by the Food and Drug Administration (Nusinersen—Spinraza; Onasemnogene abeparvovec or AVXS-101—Zolgensma; Risdiplam—Evrysdi): although assuring remarkable results, the therapies show some important limits including high costs, still unknown long-term effects, side effects and disregarding of SMN-independent targets.