UBA1 and proximal spinal muscular atrophy: UBA1 suppression in iPSC derived human SMA motor neurons, non-SMN dependent form of SMA in human patients with UPA/UBA1 mutations45 and accumulation of UPS target protein in SMA patients due to dysregulation of UPS/UBA1 pathway46 suggesting UBA1 as an important and potentially attractive therapeutic target for SMA.