Onasemnogene abeparvovec has been approved for the treatment of spinal muscular atrophy 5q (SMA) type 1 in several countries, which calls for an independent assessment of its evidence regarding efficacy and safety.

This study results from searches conducted on databases MEDLINE, Embase, LILACS and Cochrane Library up to November 2022, supported by additional searches on registry databases and by manual searches of references listed in eligible studies. Outcomes of interest were global survival and mechanical-ventilation-free survival, improvement in motor function and treatment-related adverse events. Risk of bias was assessed via ROBINS-I and certainty of evidence via GRADE. Proportional meta-analysis models were performed when applicable.

Four reports of three open-label, non-comparative clinical trials (START, STR1VE-US and STR1VE-EU) covering 67 patients were included in review. Meta-analyses of data available in a 12-month follow-up estimate a global survival of 97.6% (95% confidence interval [CI]: 92.6, 99.9; I2 = 0%, n=67), an event-free survival of 96.5% (95%CI: 90.8, 99.5; I2 = 32%, n=66) and a CHOP-INTEND score of 40 points or less proportion of 87.3% (95%CI: 69.8, 97.8; I2 = 69%, n=67). Proportions of 61.1% (95%CI: 40, 80.2; I² = 62%, n=67) of serious adverse events and of 58.4% (95%CI: 46.5, 69.8; I2 = 78%, n=67) of treatment-related adverse events are estimated. Despite the significant effect magnitude, reviewed studies were assessed as high risk of bias and as having very low certainty of evidence due to imprecision and risk of bias.

Reduced sample size and follow-up time offer uncertainties as regards the long-term benefits of the gene therapy, which strongly calls for the monitoring and assessment of results in clinical practice.