Social preference weights for treatments in Fabry disease in the UK: a discrete choice experiment

Fabry disease is a rare inherited lysosomal storage disorder caused by deficiency of α-galactosidase A. Effective enzyme replacement therapies are available that are administered intravenously. However, a new oral treatment is being developed as an alternative option for patients with amenable mutations. This study was designed to understand the value that people place on the different features of treatments for Fabry disease.

A discrete choice experiment (DCE) was designed to assess the importance of different aspects of treatments for Fabry disease. The attributes included overall survival, mode of administration, treatment related reactions, treatment related headaches and risk of antibody formation. Attributes were combined using a published orthogonal array into choice sets. A research panel was used to survey the UK general public. The mixed logit model was used to estimate strength of preference for the attributes and marginal rates of substitution (MRSs). Disutilities were estimated from the DCE data for changes in each attribute.

The sample (n = 506) was broadly representative of UK demographics. The logit model revealed that all attributes were significant predictors of choice. Participants were significantly more likely to choose a treatment which meant an increase in their life expectancy by 1 year (odds ratio = 1.574; 95% CI = 1.504-1.647) and significantly less likely to choose self-administered intravenous (IV) treatment compared to an every other day tablet (OR = 0.426 95% CI = 0.384-0.474). Estimated disutilities were -0.0543 (self-administered infusion), treatment related headaches 12 times a year (-0.0361) and infusion reactions six times a year (-0.0202).

The survey revealed a significant preference for oral treatment compared with IV even in the context of a treatment that can extend overall survival. MRSs were used as a basis for estimating disutilities associated with changes in attribute levels which could be used to weight QALYs. It is possible that other important treatment attributes are missing from this research which may have provided further insights. It would also be useful to extend this research to include Fabry disease patients so their preferences can be assessed against the societal perspective.