Estimating health state utilities for aromatic L-amino acid decarboxylase deficiency (AADCd) in the United States.

BACKGROUND

AADCd is a rare neurometabolic disorder presenting in infancy. Children with AADCd have motor dysfunction and development delays that result in the need for lifelong care; quality of life is greatly impacted. Current characterizations of health-related quality of life and associated health state utilities (HSUs) may be underestimated in AADCd. Accurate characterization of AADCd burden is important when evaluating the benefits of treatment, especially the improvements observed with the recently approved disease-modifying therapy eladocagene exuparvovec. 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 first update previously published health state vignettes, then estimate AADCd HSUs in the United States (US).

METHODS

Existing vignettes for five AADCd health states were updated based on the review of published literature and clinician/caregiver input. Health states included: "bedridden/no motor function," "head control," "sitting unassisted," "standing with support," "walking with assistance." Online composite TTO interviews were conducted 1:1 with adults 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 TTO scores were calculated for each health state, and regression models were used to estimate disutility associated with use of feeding tube.

RESULTS

Following revision of the vignettes, 120 participants completed the TTO task (mean age: 47 years; 50% female; 70% White); characteristics were not significantly different from US population norms in terms of age, sex, race or ethnicity. Six participants who appeared to misunderstand the exercise were excluded. Mean (SD) HSUs were: -0.258 (0.534) for bedridden state, -0.155 (0.569) for head control, 0.452 (0.523) for sitting unassisted, 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.