Real-Life Outcome After Gene Replacement Therapy for Spinal Muscular Atrophy: A Multicenter Experience

Background: Onasemnogene abeparvovec-xioi (OA) has been available since 2019 as a gene replacement therapy for individuals with spinal muscular atrophy (SMA) under age two years. We aim to expand upon the sparse knowledge about its safety and clinical efficacy. Methods: The clinical outcome data of all the individuals with SMA who were treated with gene therapy in four tertiary hospitals in Israel were retrieved and analyzed. Results: The study participants included 25 individuals who received the gene therapy between age 11 days and 23 months and whose median follow-up duration was 18.0 (interquartile range [IQR], 12.4 to 18.3) months. Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders scores increased by a median (IQR) of 13 (8 to 20) points at the last follow-up compared with baseline. None of the patients experienced regression in motor abilities after gene therapy, which was generally well tolerated. There was gradual improvement in motor function, especially among presymptomatic patients (P ≤ 0.001) whose disease duration was shorter (≤8 months) before receiving gene therapy (P ≤ 0.001) and who did not experience recurrent infections and illnesses in the months following treatment (P ≤ 0.001). Conclusions: OA was well tolerated and led to favorable functional motor outcomes at six to 24 months after treatment initiation. Better progress in motor function was observed in individuals who received OA earlier and who were presymptomatic, irrespective of the SMN2 copy number or type. Our results further strengthen the clinical efficacy of OA and reinforce the importance of early recognition of SMA via newborn screening programs.