SMN1 and proximal spinal muscular atrophy: In the development of SMA, the SMN protein plays an important role in pre-mRNA processing, because the biogenesis of spliceosomal snRNPs is promoted by the SMN complex [14, 18, 19], within which SMN forms oligomers and directly interacts via its N-terminus with Gemin2 and via its Tudor domain with spliceosomal (Sm) proteins [13, 20, 21].