For thousands living with spinal muscular atrophy who aged out of early approvals, the FDA’s greenlight of an intrathecal gene therapy redrew the treatment map and challenged long‑held limits. The authorization of Itvisma, an intrathecal formulation of onasemnogene abeparvovec for patients two years and older with a confirmed SMN1 mutation, signaled a broader path for gene replacement beyond infancy. SMA stems from a missing or defective SMN1 gene, leading to inadequate SMN protein and progressive muscle weakness that can compromise movement, breathing, and swallowing. By delivering a functional copy of SMN1, Itvisma aimed to increase protein expression and preserve abilities at risk of decline. Crucially, the therapy uses a single intrathecal injection and does not require dose adjustments for age or body weight, reducing complexity for clinicians and making one‑time intervention feasible for adolescents and adults.
What expanded access could change
Broadening eligibility reshaped expectations for care teams managing a heterogeneous SMA population that includes teenagers and adults with varying baselines and comorbidities. Earlier gene therapy milestones mostly centered on infants, while older patients relied on chronic treatments that demand consistent adherence. In contrast, a one‑time dose offered a practical alternative, especially where access, logistics, or adherence have been barriers. Two phase 3 studies supported approval, demonstrating statistically significant improvements in motor function and stabilization through 52 weeks, outcomes that resonated with clinicians who measure success not only by scale scores but also by preserved independence in daily life. Moreover, the lack of body‑weight adjustments simplified preparation across a wide range of patients. Yet, expectations required calibration: gene replacement is not a cure, and gains may be incremental, functional, and context‑specific.
How the decision reframed therapy and next steps
The approval framed gene therapy as a durable option in older SMA, and it also widened the lens for neurological gene medicine more broadly. Centers now had reason to refine referral pathways, expand intrathecal expertise, and align multidisciplinary follow‑up, because real‑world benefit hinged on timing, patient selection, and coordinated rehabilitation. Payers, too, faced new questions about one‑time pricing versus lifetime management, while registries and post‑marketing studies were positioned to clarify durability and identify which patients derived the most sustained benefit. For people living with SMA—about 9,000 in the U.S.—this decision shifted the balance toward earlier intervention in those who once had few choices. The moment marked another step in a six‑year evolution of SMA therapeutics and set the stage for pragmatic, outcome‑driven use of gene replacement in older patients.
