SMN1 and proximal spinal muscular atrophy: Onasemnogene abeparvovec (Zolgensma) is another gene replacement therapy that delivers the functional copy of survival of motor neuron 1 (SMN1) gene using AAV9 for the treatment of spinal muscular atrophy (SMA), a devastating neuromuscular disease (Hoy, 2019; Day et al., 2021; Figure 1A).