The phase 3b STRENGTH study evaluated the intrathecal application of the onasemnogen abeparvovec in treatment-experienced patients with spinal muscular atrophy (SMA). The results showed that this form of administration has a favorable safety profile, which is consistent with previous findings in treatment-naïve patients. The intrathecal onasemnogen abeparvovec thus represents a potential additional treatment option for this group of patients. This gene drug uses a viral vector to deliver a functional copy of the SMN1 gene directly into the cerebrospinal fluid. Treatment is aimed at replacing the missing SMN protein, which is insufficient in SMA. Clinical experience to date indicates the long-term efficacy and safety of onasemnogen abeparvovec. This study expands the treatment options for SMA even for patients who have already undergone other treatment. The results confirm the importance of gene therapy in the management of SMA.