Health Values for AADC Deficiency Calculated by UK Researchers

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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A trio of researchers in the U.K. has calculated health utilities for AADC deficiency, a quantitative measure of health value that will be useful for assessing the economic health value of future treatments.

Results were published in the study “Eliciting health state utilities for Aromatic L-amino Acid Decarboxylase (AADC) deficiency: a UK vignette study,” in the Journal of Patient-Reported Outcomes.

“Health utility” or “health state utility” is a measure that quantitatively captures the value that people place on their health or state of health. Typically, these measures range from 0 (death) to 1 (perfect health). Health utility estimates are useful for assessing the economic impact of treatments.

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However, “there have been no published studies describing health (state) utilities for patients with AADC deficiency,” the researchers wrote. “The aim of this study, therefore, was to derive health state utilities for AADC deficiency.”

The trio of scientists conducted a survey of people in the U.K. Survey participants were presented with five vignettes representing different states that can occur in AADC deficiency. In order of most to least severe impact on health, the five vignettes were bedridden, head control, ability to sit unaided, standing with support, and walking with assistance.

Health utilities were calculated using two methods called time trade-off (TTO) and standard gamble (SG). In TTO, respondents are asked to imagine that they have a certain amount of time to live in a given health state and are asked how much of that time they would be willing to give up for the remainder to be spent in perfect health. Similarly, SG asks about how much risk of instant death respondents would be willing to accept for a hypothetical treatment that could restore perfect health.

A total of 1,598 people responded to the survey; however, about a fifth of responses were excluded because they were incongruent (i.e., respondents gave bedridden a higher health utility than walking with assistance). Of the results analyzed, more than half (59.8%) of respondents were female, and the average age was 44.2 years. About one in four respondents was a parent.

Results showed that, based on TTO, the difference in health utility of moving from head control to sitting unaided was about 0.1. For the remaining vignettes, the difference from the next-best state was about 0.05.

Results from SG were generally similar, though most values were slightly higher than for TTO estimates due to differences between these methods.

“Taken together the results from this large, broadly UK representative sample showed an increase in the utility values as the health states improved,” the researchers concluded.

Other analyses showed that results were broadly consistent across demographics, though some differences were noted. For example, female respondents and parents tended to rate health utilities higher than males or nonparents, respectively.

“To the authors knowledge, this is the first study to derive health state utilities for AADC deficiency, and is, therefore by definition, also the largest study of its kind,” the researchers concluded.

The scientists pointed out that, in addition to AADC deficiency, these calculations “may also provide beneficial insights for deriving health (state) utilities in other rare conditions such as spinal muscular atrophy (SMA) where similar difficulties may be encountered.”

The team noted several limitations, including the reliance on responses gathered via the internet and the fact that the survey assessed health states overall rather than individual symptoms, which may or may not be affected by given treatments.

“Further research is required to determine the exact drivers in terms of the symptoms and milestones impacting the most on the health state utilities,” the researchers wrote.

This study was funded by PTC Therapeutics, which is developing a gene therapy for AADC deficiency called PTC-AADC.

“These robust data will be utilised in an economic evaluation of a gene therapy for AADC deficiency,” the scientists wrote.