Outcomes of early-treated infants with spinal muscular atrophy: A multicenter, retrospective cohort study

Introduction/Aims: While prompt identification and treatment of infants with spinal muscular atrophy (SMA) can ameliorate outcomes, variability persists. This study assessed management and outcomes of early-treated infants with SMA. Methods: We analyzed retrospective data at 12 centers on infants with SMA treated at age ≤6 weeks from August 2018 to December 2023. Results: Sixty-six patients, 35 with two SMN2 copies and 31 with ≥3 SMN2 copies, were included. Twenty-five (38%, 22 with two SMN2 copies), had SMA findings before initial treatment which was onasemnogene abeparvovec in 47 (71%) and nusinersen in 19 (29%). Thirty-two received sequential or combination treatments, including 16 adding nusinersen or risdiplam due to SMA findings following onasemnogene abeparvovec. All sat independently. Compared to children with ≥3 SMN2 copies, those with two SMN2 copies were less likely to walk (23/34 [68%] vs. 31/31 [100%], p <.001) and less likely to walk on time (9/34 [26%] vs. 29/31 [94%], p <.001); one non-ambulatory child was <18 months old and was excluded from this analysis. No patients required permanent ventilation or exclusively enteral nutrition; six required nocturnal non-invasive ventilation and four utilized supplemental enteral nutrition, all with two SMN2 copies. Discussion: Early treatment of infants with SMA can improve outcomes as indicated by our cohort, all of whom sat independently and are without permanent ventilation. However, our study demonstrates ongoing disability in most children with two SMN2 copies despite early monotherapy and emphasizes the need for additional research, including earlier monotherapy, initial combination therapy, prenatal treatment, and non-SMN modifying treatments.