The severity of SMA correlates with the level of SMN, a multifunctional protein implicated in regulation of small nuclear heteronuclear ribonucleoprotein (snRNP) biogenesis, transcription, translation, stress granule formation, signal transduction and axonal transport of mRNA (references in Seo et al., 20133). This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.