The Impact of Activated Phosphoinositide 3-Kinase δ Syndrome (APDS) on Health-Related Quality of Life (HRQoL): Elicitation of Health State Utility Values Through Time Trade-Off (TTO) and EQ-5D

IntroductionActivated phosphoinositide 3-kinase delta (PI3K delta) syndrome (APDS) is an ultra-rare inborn error of immunity. APDS is a chronic, heterogeneous, and progressive disease, with individuals experiencing different combinations of multisystemic clinical manifestations which advance over time. To date, there are no published utility values for APDS and there are limited data detailing the long-term effects and impact of APDS on health-related quality of life (HRQoL). This study sought to quantify the impact of individual and combined manifestations on the HRQoL of people with APDS.MethodsTo mitigate the challenges of measuring HRQoL in a rare disease, health state vignettes were developed through interviews with people with APDS and the published literature, and validated by experts, to represent individual or combinations of manifestations frequently experienced by people with APDS. Two valuation methods were then employed to elicit utility values for the health states: EQ-5D with clinical experts from France, Spain, and the UK (N = 4), and time trade-off (TTO) with members of the UK general public (N = 100).ResultsThe results of both EQ-5D and TTO exercises highlight the substantial HRQoL impact of APDS, particularly in those experiencing multiple concurrent manifestations or those diagnosed with lymphoma. Mean utility values ranged from 0.897 to - 0.109 in the EQ-5D exercise and 0.870 to 0.330 in the TTO exercise. Overall, the ranking of the health states by utility values was generally consistent between EQ-5D and TTO exercises. However, points of variance were observed for utility values for severe health states, e.g. those including lymphoma (one of the primary causes of death in APDS) ranged from 0.430 to - 0.109 in the TTO and EQ-5D exercises, respectively.ConclusionThis is the first study to indirectly elicit utility values in APDS through valuation by the general population and clinical experts. This expands on the current literature for APDS by providing an overview of how HRQoL declines with disease progression and increasing number of manifestations.