Estimating Health State Utilities (HSUS) for Aromatic L-Amino Acid Decarboxylase Deficiency (AADCD) in the United States

OBJECTIVES: AADCd is a rare neurometabolic disorder with infantile onset. Patients have motor dysfunction and development delays that substantially impact their ability to be independent, with the most severe patients potentially bedridden and having greater mortality risk. Given the challenges of estimating utilities in pediatric rare disease populations, time-trade-off (TTO) vignette methods may be used to elicit HSUs in AADCd for assessing the value of new treatments. This study aimed to estimate AADCd HSUs in the United States (US).

METHODS: Vignettes for five AADCd health states were used based on published literature and clinician/caregiver input. Health states included: “bedridden/no motor function,” “head control,” “sitting unaided,” “standing with support,” “walking with assistance.” TTO interviews were conducted 1:1 over Zoom with adult participants from the US general public. Participants ranked health states in order of preference using a visual analog scale, then were presented with health state vignettes to elicit utilities using TTO. Mean (standard deviation [SD]) TTO scores were calculated for each health state, and regression models were used to explore potential utility predictors.

RESULTS: 120 participants completed the TTO task (median age: 48 years; 50% female; 70% White); characteristics were not significantly different from US population norms. Six participants who appeared to misunderstand the exercise were excluded. Mean (SD) health states utilities were: -0.258 (0.534) for bedridden state, -0.155 (0.569) for head control, 0.452 (0.523) for sitting unaided, 0.775 (0.242) for standing with support, and 0.796 (0.235) for walking with assistance. The need for a feeding tube was associated with a disutility of 0.07.

CONCLUSIONS: This study implemented TTO methods to estimate utilities for five health states, which reflect the burden and impact of AADCd. The range in values from the most to least severe health state suggests that there is potential for effective treatments to substantially improve quality of life in these patients.