PTC Therapeutics has developed and validated tools to help assess health-related quality of life (HRQoL) in people with aromatic l-amino acid decarboxylase (AADC) deficiency.
In addition, these health tools are expected to help determine the cost-effectiveness ratio of future treatments for this rare genetic disease.
The new tools will provide important insights for researchers working to develop therapies for AADC deficiency, according to Stuart W. Peltz, PhD, CEO of PTC.
“These insights are critical so that the best treatments can be made available to patients,” Peltz, said in a press release.
Of note, PTC’s investigational gene therapy PTC-AADC for AADC deficiency, which resulted in positive findings in clinical trials, is currently under regulatory review in Europe and also will soon be reviewed by regulatory authorities in the U.S.
“PTC is committed to ensuring patients can access clinically differentiated treatments such as our gene therapy for AADC deficiency which, if approved, promises to become the standard of care,” Peltz said.
Studies on these AADC deficiency health tools were recently presented in four company-sponsored posters at the Virtual ISPOR Europe 2020 Conference, available online through Dec. 31.
Capturing patients’ HRQoL is critical in evaluating the impact of a treatment. However, the rarity of AADC deficiency and the fact that its symptoms mainly appear in early infancy challenges the assessment of HRQoL through ratings from patients or proxy caregivers.
HRQoL data may instead be estimated using health utilities — cardinal values of health states that may be experienced by patients, ranging from 0 (indicating death) to 1 (full health). These are also used to determine quality-adjusted life-years, a measure of disease burden that multiplies the length of time spent in a given health state by the life quality associated with that state.
An estimate of quality-adjusted life-years is key in assessing a therapy’s cost-effectiveness. It’s also one of the main outcome measures used in funding decision-making by regulators, particularly in countries with publicly funded health care systems, such as England and France.
Developing health utilities involves two main steps: defining a set of health states and disease aspects of interest, and valuing them to determine their weight.
Researchers at PTC and the York Health Economics Consortium, in the U.K., set out to complete the first step by identifying relevant health states and aspects of AADC deficiency based on published literature and input from patients, caregivers, and clinicians.
In the poster, “Deriving Vignettes For A Rare Disease Using Parent, Caregiver And Clinician Interviews To Evaluate The Impact On Health-Related Quality Of Life,” the researchers reported the identification of five relevant health states — bedridden, head control, sitting unsupported, standing with assistance, and walking with assistance. They also identified six disease aspects, specifically mobility, muscle weakness, oculogyric crises, feeding, cognitive impairment, and crying. Of note, oculogyric crises are involuntary upward eye movements characteristic of AADC deficiency.
The weight of these health states and disease aspects, or AADC deficiency health utilities, were then assessed in a representative sample of the U.K. population, numbering about 1,600 people. These assessments were done, online, through two types of studies, called vignette studies and discrete choice experiments (DCEs).
Vignette studies use short descriptions of situations or people (vignettes) that are usually shown to respondents within surveys to elicit their judgments about the scenarios. Meanwhile, a discrete choice experiment is a quantitative method increasingly used in healthcare to elicit preferences from participants without directly asking them to state their preferred options.
The results of the vignette study were presented in the poster, “A Vignette Study To Derive Health State Utilities For Aromatic L-Amino Acid Decarboxylase (AADC) Deficiency In The United Kingdom (UK),” while those of the DCE were shown in the poster, “A Discrete Choice Experiment To Derive Health State Utilities For Aromatic L-Amino Acid Decarboxylase (AADCd) In The United Kingdom.”
After successfully deriving AADC deficiency health utilities using these studies, the researchers aimed at validating them in France. The steps taken were described in a poster, titled “Validating Vignettes For A Rare Disease Using Clinician Interviews To Evaluate The Impact On Health-Related Quality Of Life In Aromatic L- Amino Acid Decarboxylase (AADC) Deficiency In France.”
The health states and disease aspects previously developed and validated in the U.K. were translated to French, after which their content and translation were validated by four French clinicians.
The results showed that the health state descriptions were largely supported by the French clinicians. However, six changes were suggested, including the addition of “tiredness” as a symptom to two health states, as well as minor revisions to the language translation.
While this study enabled the validation of these health tools previously developed for the U.K., “it also showed that it is important to validate with local experts the language when planning to derive utilities for a cost-effectiveness model of an [AADC deficiency] treatment in a specific country,” the researchers wrote in the abstract.
According to the posters’ abstracts, the developed health utilities will be used to estimate HRQoL in AADC deficiency patients in both countries, as well as the cost-effectiveness ratio of a future treatment for this patient population.
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