The phase 3 STEER study evaluated the efficacy and safety of a single intrathecal dose of the onasemnogen abeparvovec in previously untreated patients with spinal muscular atrophy (SMA). The results showed that the treatment significantly improved motor function in children and adolescents compared to sham treatment. The safety profile was similar and acceptable, with no serious adverse effects. Onasemnogen abeparvovec is a gene therapy that targets the genetic cause of SMA by complementing the missing SMN1 gene, thereby supporting motor neuron function. The study confirmed that this treatment can improve patients' quality of life and slow the progression of the disease. The results are particularly significant for patients who have not yet been treated with other methods. This therapy represents an important advance in the treatment of SMA, a genetic neurodegenerative disease that causes muscle weakness and atrophy.