SMN2 and proximal spinal muscular atrophy: For this reason, increasing SMN protein production by SMN2 is the target of two out of the three recently approved therapies for the treatment of SMA, being the third directed to reintroduce SMN1 gene (Finkel et al., 2017; Mendell et al., 2017; Darras et al., 2021; Mercuri et al., 2021).