OBJECTIVES: Spinal muscular atrophy (SMA) is a rare neurodegenerative disease. Individuals with severe Type 1 SMA (‘infantile onset’) rarely meet key developmental motor milestones, such as sitting unassisted. The recent approval of disease-modifying therapies (DMTs) for this indication has highlighted the importance of robust survival data to inform long-term disease models and economic analyses. The aim of the current analysis was to review existing evidence to generate a pooled survival estimate in individuals with Type 1 SMA.

METHODS: A systematic review was conducted in August 2019 to identify studies with published Type 1 SMA survival curves. Survival curves were scanned in GetData Graph Digitizer to provide estimates of x and y coordinates. Pseudo-individual patient data (IPD) were generated by applying a published algorithm to the coordinates from each curve.

RESULTS: Twenty studies, published between 1994 and 2018, conducted in Europe (n=8), USA (n=5), Asia (n=4), Australia (n=1), or multiple territories (n=2) were identified. The number of patients enrolled ranged from 13 to 1,021 (total cohort, N=2,364) and mean age at onset was from 28 days to 3.1 months, where reported. Although heterogeneity was observed in the individual survival estimates, median survival was <3 years in 14/20 studies. Pooling of IPD across studies indicated a median survival of 1.61 years (95% confidence interval: 1.47–1.80) with approximately 31% of patients surviving >5 years.

CONCLUSIONS: The current analysis provides a robust estimate of median survival in individuals with Type 1 SMA. The heterogeneity in individual survival estimates is likely due to study design differences, Type 1 SMA subtype inclusion, and changes in standard of care over time and across countries. Changes include DMT approval and the proactive use of ventilation, indications for which are followed differently amongst different countries. Appropriate use may lead to prolonged survival in patients with Type 1 SMA.