SMN2 and proximal spinal muscular atrophy: SMN highly conserved domains include a short segment near the N-terminus that is responsible for binding with high affinity to Gemin2 [16]; the Tudor domain that recognizes symmetric dimethylarginine modifications in arginine/glycine (RGG) rich regions in a number of proteins involved in RNA processing, including the Sm proteins [17,18]; and the evolutionarily conserved C-terminal YG-box that is required for SMN oligomerization and is impaired in carriers of some SMN variants that lead to SMA [19,20].