With the structural analysis, this article highlights three residues of SMN (Asp44, Glu134 and Gln136), and the electrostatic basis (Fig 3) of how the SMA-linked missense mutations of the three residues cause structural/functional deficiency of SMN, and also a possibility of SMN’s Lys45 and Asp36 acting as two electrostatically stabilizing clips at the SMN-Gemin2 complex structure interface. This evidence concerns the gene SMN2 and proximal spinal muscular atrophy.