Onasemnogene abeparvovec is an approved one-time intravenous infusion therapy indicated for the treatment of patients with 5q spinal muscular atrophy (SMA) with a biallelic mutation in the survival motor neuron 1 (SMN1) gene and a clinical diagnosis of SMA type 1, or patients with 5q SMA with a biallelic mutation in the SMN1 gene and up to three copies of the SMN2 gene. The gene discussed is SMN1; the disease is proximal spinal muscular atrophy.