SMN2 and proximal spinal muscular atrophy: A preclinical proof-of-principal study using SMNΔ7 (Smn−/−, SMN2+/+, SMNΔ7+/+) mice, a mouse model of severe SMA, achieved increased SMN protein levels in spinal motor neurons via single intracerebroventricular (i.c.v.)administration of nusinersen.