Methodological Challenges in the Economic Evaluation of a Gene Therapy for RPE65-Mediated Inherited Retinal Disease: The Value of Vision

The emergence of gene therapies challenge health economists to evaluate interventions that are often provided to a small patient population with a specific gene mutation in a single dose with high upfront costs and uncertain long-term benefits. The objective of this study was to illustrate the methodological challenges of evaluating gene therapies and their implications by discussing four economic evaluations of voretigene neparvovec (VN) for the treatment of RPE65-mediated inherited retinal disease. The checklist for economic evaluations of gene therapies of Drummond et al. was applied to the economic evaluations of VN performed by US Institute for Clinical and Economic Review, two country adaptations of the company model in the UK and the Netherlands, and another US publication. The main differences in methodological choices and their impact on cost-effectiveness results were assessed and further explored with sensitivity analyses using the Dutch model. To enable comparison between the economic evaluations, costs were converted to US dollars. Different methodological choices were made in the economic evaluations of VN resulting in large differences in the incremental cost-effectiveness ratio varying from US$79,618 to US$643,813 per QALY. The chosen duration of treatment effect, source of utility values, discount rate and model structure had the largest impact on the cost-effectiveness. This study underlines the findings from Drummond et al. that standard methods can be used to evaluate gene therapies. However, given uncertainty about (particularly long-term) outcomes of gene therapies, guidance is required on the acceptable extrapolation of treatment effect of gene therapies and on how to handle the uncertainty around this extrapolation in scenario and sensitivity analyses to aid health technology assessment research and align submissions of future gene therapies.