Onasemnogene abeparvovec (OA), which involves the adeno-associated virus (AAV) 9-mediated transfer of a new copy of the SMN1 gene to the host, was approved in 2020 as the first gene replacement therapy for intravenously treating patients with 5q-SMA with biallelic SMN1 mutations and clinically diagnosed with SMA type 1 or patients with ≤ 3 SMN2 gene copies (including presymptomatic newborns). The gene discussed is SMN1; the disease is spinal muscular atrophy, type 1.