Development of the Fabry Disease Patient-Reported Outcome (FD-PRO): a new instrument to measure the symptoms and impacts of Fabry Disease

BACKGROUND: The systematic collection of disease-specific symptoms and impacts on the lives of patients with Fabry Disease (FD) can offer unique insights into the patient experience, yet no disease-specific tool to measure FD symptoms exists. This study describes the development of the Fabry Disease Patient-Reported Outcome (FD-PRO). METHODS: A targeted literature search, interviews with key opinion leaders (KOLs), and concept elicitation (CE) interviews with patients identified the most frequent signs and symptoms associated with FD and their impact on daily life. Cognitive interviews evaluated patients’ ability to understand the FD-PRO instructions and respond to the items on the draft FD-PRO instrument. RESULTS: The targeted literature search identified key signs and symptoms in domains that were confirmed in KOL interviews. In CE interviews with 37 treated and treatment-naïve patients, neuropathic pain symptoms (95% treated, 82% treatment-naïve), temperature intolerance (95% treated, 88% treatment-naïve), energy difficulties (95% treated, 94% treatment-naïve), hearing/vision impairment (95% treated, 71% treatment-naïve), and gastrointestinal symptoms (80% treated, 59% treatment-naïve) were most frequently mentioned. Results were similar for men and women in both treated and treatment-naïve groups. While treatment-naïve patients in general expressed fewer and milder symptoms compared to treated patients, the overall sets of symptoms expressed by the two groups were similar. The most severe symptoms were neuropathic pain, stomach pain, burning pain, and fatigue. The most bothersome symptoms were stomach pain, breathing difficulty, fatigue, neuropathic pain, and constipation. The most frequent impacts were in the work/school limitations domain for both treated and treatment-naïve patients. The impacts with the highest difficulty ratings were stress, limited outdoor activity, and guilt. Cognitive interviews with 14 treated and treatment-naïve patients resulted in the refinement of FD-PRO items and language. CONCLUSIONS: The FD-PRO is a novel, disease-specific instrument that measures the patient experience in Fabry disease. Such tools are valuable in capturing the burden of disease in patients with FD and demonstrating the value of treatment in clinical trials.