What question did this study set out to answer?

This research aims to develop and evaluate a patient-reported outcome (PRO) measure for Glycogen Storage Disease Type Ia (GSDIa).

April 16, 2026Open Access

Development and Preliminary Psychometric Evaluation of the Glycogen Storage Disease Type Ia Functional Assessment Diary (GSD FAD)

DTDiane M. Turner‐BowkerUltragenyx Pharmaceutical (United States)SEShayna EganUltragenyx Pharmaceutical (United States)JBJ ButlerUltragenyx Pharmaceutical (United States)

Key Points

This research aims to develop and evaluate a patient-reported outcome (PRO) measure for Glycogen Storage Disease Type Ia (GSDIa).
Conducted a literature review and online survey to gather patient perspectives.
Performed concept elicitation (CE) interviews to inform questionnaire development.
Engaged in cognitive debriefing (CD) interviews for item interpretation and understanding.
Evaluated psychometric properties using Phase 3 trial screening/baseline data.
Identified key burdens of hypoglycemia and cornstarch regimen from patient feedback.
Draft GSD FAD included 36 items, with revisions based on interpretation issues.
Three domain scores showed acceptable reliability and validity, but noted ceiling effects.

Abstract

Diane M Turner-Bowker,1 Shayna Egan,1 Jessica Butler,1 Adrian Jewett,2 Deepali Mitragotri,3 Brandon Foster,2 Alison Skrinar,1 Christina Theodore-Oklota1 1Endpoint Development and Strategy, Ultragenyx Pharmaceutical Inc., Novato, CA, USA; 2Patient Centered Outcomes, Lumanity, Long Beach, CA, USA; 3Biostatistics revisions to the GSD FAD addressed interpretation issues. Three domain scores (Symptoms Total Score, Sleep Impacts Total Score, and Daily Impacts Total Score) showed acceptable reliability and validity but had notable ceiling effects that may limit responsiveness in some settings.Conclusion: The GSD FAD is a novel, content-valid PRO that measures the humanistic burden of GSDIa and cornstarch treatment regimen, including the signs/symptoms of hypoglycemia and their impact on health-related quality of life (HRQoL) in individuals â¥ 8 years with GSDIa, that yields reliable and valid scores. While developed in a trial setting, the GSD FAD has potential for use in nutritional, behavioral, and/or educational applications.Keywords: GSDIa, patient-reported outcome, content validity, psychometric, reliability, validity

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