MUSK and proximal spinal muscular atrophy: The role of agrin/LRP4/MuSK/Dok7 signalling pathway in SMA disease was first underlined by the observation that agrin Z+ exon is mis-spliced in spinal motoneurons of SMA model mice37, that can be corrected by the co-expression of AAV-9 U7-specific Lsm10 and Lsm11 proteins38.