Eliciting Health State Utilities for Aromatic L-Amino Acid Decarboxylase (AADC) Deficiency: A Vignette Study in France.

Purpose: Health-related quality of life (HRQoL) is difficult to measure in rare diseases, especially in paediatric populations, yet capturing HRQoL is critical to evaluating treatment, including the cost-effectiveness of treatments. Given the ultra-rare nature of AADC deficiency indirect elicitation of HRQoL data through proxy caregiver/parent ratings is not feasible. In these circumstances, HRQoL data may be derived through vignette studies using the general population. The aim of the study was to generate health utility values specific for France for AADC deficiency using vignettes.

Methods: The study was completed online by panel participants from a French representative sample. Five health state vignettes, reflecting key milestones in the eladocagene exuparvovec clinical trials and economic model, were presented to the participants: "bedridden", "head control", "sitting unsupported", "standing with assistance" and "walking with assistance". The vignettes had been previously developed with input from parents of patients with AADC deficiency, patients and expert opinion. Participants also completed the Health Utilities Index-3 for the "bedridden" health state.

Results: A total of 1001 participants (51% females; mean age 46 years) completed the vignettes. Utilities increased linearly as the health state improved for both the time trade-off (TTO): 0.47 (standard deviation, SD 0.36) to 0.54 (SD 0.36) and standard gamble (SG): 0.61 (SD 0.29) to 0.67 (SD 0.27). A significant minority had incongruent responses (high utilities for the bedridden compared to walking health states) for the vignette (27%). When these were removed, the TTO health utilities (N=729) ranged from 0.39 (SD 0.36) to 0.56 (SD 0.38) and 0.61 (SD 0.30) to 0.69 (SD 0.27) for the SG.

Conclusion: Health utilities were derived for AADC deficiency which will be used for a cost-effectiveness model of an AADC deficiency treatment.