OBJECTIVES: Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder and is considered one of the most common genetic causes of infant mortality. Onasemnogene Abeparvovec-xioi (OA) is a gene therapy showing promising health outcomes for SMA treatment, with a list price of approximately €2,000,000. This study aims to provide a cost-effectiveness analysis in the Netherlands for the treatment of SMA type I with OA with newly published data.

METHODS: A Markov model with five health states was replicated to analyze the costs and outcomes for patients diagnosed with SMA Type I. The analysis was conducted from a societal perspective in the Netherlands over a time period of 99 years. Both one-way and probabilistic sensitivity analyses were conducted to assess the uncertainties associated with the model's parameters. A scenario analysis was performed to evaluate the potential benefits of early treatment.

RESULTS: Base-case incremental cost-effectiveness ratio (ICER) of OA was €257,717 per quality-adjusted life year (QALY) compared to best supportive care (BSC). The ICER of OA from the early treatment scenario was €127,107 compared to BSC. Both are above the Dutch willingness-to-pay (WTP) reference value of €80,000. Key drivers influencing the ICERs were the costs of OA treatment and utility and cost values of ‘sitting independently’ health state.

CONCLUSIONS: Based on this model, treatment with OA supports the notion that it offers significant improvements in disease progression, motor skills, and quality of life compared to BSC. A reduced ICER of almost 27% is observed compared to the HTA conducted by the Dutch Health Care Institute. However, it is not cost-effective under the Dutch WTP threshold. Limited availability of clinical trial data, characterized by small sample sizes and short follow-up periods, causes great uncertainty. Decision-makers should find a suitable balance between these uncertainties and the cost they are willing to pay for the treatment of rare diseases.