Clinical trials using AAV gene therapy have been completed or are ongoing for several CNS disorders including GM1 and GM2 gangliosidoses, Canavan disease,1 Batten disease,2 Sanfilippo syndrome,3 aromatic l-amino acid decarboxylase (AADC) deficiency,4 Parkinson's disease,5 spinal muscular atrophy (SMA),6,7 giant axonal neuropathy (GAN),8 Rett syndrome, and others. Here, DDC is linked to proximal spinal muscular atrophy.