Long-term adherence, safety and effectiveness of nusinersen in spinal muscular atrophy patients: a population-based study

Nusinersen was the first disease modifying treatment approved for 5q spinal muscular atrophy (SMA). Long-term results of broad populations, particularly for adolescents and adults, remain limited. We conducted a population-based, ambispective observational study of all SMA patients living in the Valencian Community (Spain) between September 2017 and December 2022 and follow-up until December 2025. Demographic, clinical and motor outcomes using revised SMA Functional Composite Score (SMA-FCR) were collected. Patients were classified as responders or non-responders. The risk for nusinersen discontinuation was assessed with a Bayesian model, and SMA-FCR trajectories with mixed linear regression. Of 72 patients included, 18 were <12 years old (all treated with nusinersen) and 54 were [&ge;]12 years (28 treated; 26 untreated) at the baseline visit. After a median of 7 years, all patients <12 years were classified as responders versus 68% of patients [&ge;]12 years. Discontinuation rates were 11% in children compared to75% in the older cohort. In patients [&ge;]12 years, reasons for discontinuation included: treatment burden (71%), and loss(53%) or lack of benefit (43 %). Lower baseline SMA-FCR (expEstimate= 0.84 [0.718,0.93], prob:1) and older age (expEstimate=1.028 [1.011,1.055], prob:1) independently predicted higher discontinuation risk. Sustained nusinersen treatment was independently associated with SMA-FCR increase, while untreated and discontinued patients showed slight deterioration over time. In this long-term population-based study, nusinersen use and persistence was high in children but declined significantly after age 12 due to treatment burden and limited efficacy. However, a proportion of adolescents and adults (those younger and with higher baseline function) experienced sustained benefit.