BackgroundAngelman syndrome (AS) is a rare, heterogenous neurogenetic condition, which significantly impacts the lives of people with AS and their families. Valid and reliable measures reporting key symptoms and functional impairments of AS are required to support development of patient-centered therapies. We describe the development of clinician- and caregiver-reported, AS-specific Global Impression scales for incorporation into clinical trials. Best practice US Food and Drug Administration guidance for measure development was followed with input from expert clinicians, patient advocates, and caregivers during content generation and refinement.ResultsInitial measurement domains for the Symptoms of AS—Clinician Global Impression (SAS-CGI) and the Caregiver-reported AS Scale (CASS) were identified from a conceptual disease model of AS symptoms and impacts, derived from interviews with caregivers and clinicians. Two rounds of cognitive debriefing (CD) interviews were performed; clinicians debriefed the SAS-CGI, with patient advocates and caregivers debriefing the CASS to ensure relevance and comprehension. Feedback was used to refine items and ensure wording was age-appropriate and captured AS-specific symptoms, as well as associated impacts and functional impairments. The SAS-CGI and CASS capture global assessments of seizures, sleep, maladaptive behaviors, expressive communication, fine and gross motor skills, cognition, and self-care, which were determined by clinicians, patient advocates, and caregivers to be the most challenging aspects of AS. Additionally, the measures include items for assessing overall AS symptoms and the meaningfulness of any change. In addition to ratings for severity, impact, and change, a notes field was included in the SAS-CGI to provide the rationale for the chosen rating. CD interviews confirmed the measures covered key concepts of AS from the perspective of clinicians and caregivers, and demonstrated that the measures’ instructions, items, and response options were clear and appropriate. Interview feedback informed adjustments to the wording of the instructions and the items.ConclusionsThe SAS-CGI and CASS were designed to capture multiple AS symptoms, reflecting the heterogeneity and complexity of AS in children 1 to 12 years old. These clinical outcome assessments have been incorporated into AS clinical studies, which will allow for the evaluation of their psychometric properties and inform further refinements if needed.