SMN1 and proximal spinal muscular atrophy: We employed two different SMA patient-derived mutations located in distinct subdomains of the SMN protein, the Tudor domain (SmnTg:V72G) and the tyrosine- and glycine-rich YG Box (SmnTg:T205I); see Fig. 1A. The Tudor domain of SMN binds symmetric dimethylarginine residues present at the C-termini of Sm proteins [37, 38], and the YG Box functions in SMN self-oligomerization [19, 22, 39, 40].