Identified as the first fully protective modifier of SMA in humans (Oprea et al., 2008), overexpression of the F-actin bundling protein Plastin 3 was found to rescue motor unit defects in both zebrafish and mouse SMA models (Oprea et al., 2008; Ackermann et al., 2013). Here, PLS3 is linked to proximal spinal muscular atrophy.