Scientists Estimate Health Utilities – Possible Economic Values – in AADC

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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A team led by scientists at PTC Therapeutics has calculated health utilities — quantitative values for assessing health — for aromatic l-amino acid decarboxylase (AADC) deficiency based on data from a survey conducted in France.

The findings, in combination with earlier work done in the U.K., could be helpful for assigning an economic value to potential treatments for this rare disease.

“This is the first study, to our knowledge, to derive robust health utilities for AADC deficiency symptoms using a large sample drawn from the general French population and to some extent contrast to the findings from a UK-based study to derive utilities using similar methods,” the researchers wrote.

The study, “A Discrete Choice Experiment to Derive Health Utilities for Aromatic L-Amino Acid Decarboxylase (AADC) Deficiency in France,” was published in the journal Patient Related Outcome Measures.

The work was funded by PTC, which currently is developing an experimental gene therapy, called PTC-AADC, for AADC deficiency.

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Health utilities are quantitative measures that are meant to reflect how much value a person places on a given state of health. These measures, which usually range from 0, or death, to 1, for perfect health, are helpful for assessing the economic impact of therapies that can alter a person’s health state.

“Cost-effectiveness evaluations of interventions require health utility data. However, in medical conditions, such as aromatic L-amino acid decarboxylase (AADC) deficiency, this presents problems due to the rarity of the disease,” the researchers wrote.

To estimate health utilities relevant for AADC, researchers at PTC, in collaboration with investigators at the University of East Anglia’s Norwich Medical School and the York Health Economics Consortium, both in the U.K., conducted a discrete choice experiment.

Basically, this is a survey in which respondents are given two or more potential health states to pick between, and is designed to give researchers an understanding of relative value. For example, the individuals surveyed might be asked to choose between severe muscle weakness with minimal cognitive impairment, as compared to less severe muscle weakness and more cognitive challenges.

Other parts of the survey assessed time trade-off (TTO) and standard gamble (SG), both of which, essentially, are measures of how much theoretical risk a person would accept for a treatment that could move them from one health state to another.

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.

By comparing the different choices that are made, researchers can calculate how much people are valuing different disease-relevant conditions. PTC had previously conducted similar studies in the U.K.

“These data will be utilised to enable improvements in health-related quality of life to be considered in a country-specific economic evaluation of a gene therapy for AADC deficiency,” the team wrote.

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A total of 1,001 adults in France answered the survey. About half (50.9%) were female, and their mean age was 45.7. Notably, individuals who were caregivers or parents of a child with a life-threatening disease were excluded from taking part.

Results of the survey showed that, generally, respondents valued mobility more than other disease-relevant aspects assessed. In other words, a decrease in mobility was associated with a steeper decrease in health utility, compared with a similar decrease for other symptoms.

The results revealed some noteworthy differences between these data and those from prior studies done in the U.K. In the U.K., uncontrolled screaming was a bigger driver of health utility changes than mobility.

A possible explanation for this is that “the UK study participants may have included parental or caregiver health-related quality of life (HRQoL) as part of their evaluation, rather than the child’s HRQoL alone,” the researchers wrote. Other differences between the groups — for example, more participants in the French study were parents (35% vs. 26.6%) — as well as cultural differences likely contributed to this divergence.

Beyond differences in specific disease aspects, overall health utilities generally were lower in the French data, meaning the value assigned to the duration of life with each disease aspect was smaller for this population.

“It is evident that the French participants were rating the health state, and consequently by inference the symptoms and impact of AADC deficiency more severely than the UK participants,” the researchers wrote. “The ‘best’ health state (‘Walking with assistance’), in particular, was rated much lower by the French participants.”

“These health utilities will subsequently be used in an economic model evaluating an AADC deficiency intervention,” the team concluded.