Early Intervention and Speed-to-Effect in Spinal Muscular Atrophy Type 1 Following Onasemnogene Abeparvovec Gene Replacement Therapy: Results of aPost-Hoc Analysis of Pooled Clinical Study Data

INTRODUCTION: Studies suggest that early intervention with disease-modifying treatment for spinal muscular atrophy (SMA) might provide the best opportunity for optimal outcomes. One such treatment is onasemnogene abeparvovec, a gene replacement therapy with durable efficacy demonstrated in clinical trials, long-term studies, and real-world data (e.g., RESTORE registry). METHODS: A pooled post-hoc analysis was conducted to assess the early post-treatment impact of intravenous onasemnogene abeparvovec on motor function and event-free survival for symptomatic infants with SMA type 1 (i.e., non-sitters). Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) scores and event-free survival were evaluated for patients enrolled in the START, STR1VE-US, and STR1VE-EU clinical trials. RESULTS: The pooled analysis set included 67 patients. Mean (SD) CHOP INTEND score at baseline was 29.3 (9.58) points. Rapid increases in mean CHOP INTEND of 7.0, 9.7, and 11.8 points were observed at 1, 2, and 3 months post-dose, respectively. At 6 months post-dose, 54/59 infants (91.5%) treated with onasemnogene abeparvovec achieved a clinically significant ≥ 4-point improvement in CHOP INTEND score from baseline, with a mean (SD) CHOP INTEND score of 44.3 (9.92) points. Patients who received onasemnogene abeparvovec had longer ventilation-free survival compared with natural history, with a statistically significant separation from the natural history cohort being maintained throughout follow-up. CONCLUSIONS: Rapid and clinically significant improvements in motor function were observed for onasemnogene abeparvovec-treated patients with symptomatic SMA type 1. Early diagnosis and treatment are essential for timely restoration and preservation of motor neurons and maximal motor function improvement.