There are three (3) AAV-based gene therapies approved for monogenic disorders, with the first one targeting lipoprotein lipase deficiency [144] (withdrawn in 2017 due to commercial issues), followed by the approval in 2017 of a treatment for RPE65 mutation-associated inherited retinal dystrophy, followed by the approval in 2019 of onasemnogene abeparvovec (ZOLGENSMA®) by replacing the missing or nonworking SMN1 gene with a new and working SMN1 gene for the treatment of spinal muscular atrophy (SMA). Here, SMN1 is linked to proximal spinal muscular atrophy.