For a study, the resulting CGI-S/I-AS scales captured 6 critical domains (behavior, gross and fine motor function, expressive and receptive communication, and sleep) defined by caregivers and expert clinicians as the most challenging for patients with Angelman syndrome (AS) and their families. Rigorous training and careful calibration for clinicians allowed the CGI-S/-I-AS scales to be reliable in the context of randomized controlled trials. The CGI-S/-I-AS scales are being utilized in a Phase 3 trial of gaboxadol for the treatment of AS. To develop adapted CGI scales specific to AS, researchers reviewed literature and interviewed caregivers and clinicians to determine the most impactful symptoms, engaged expert panels to define and operationalize the symptom domains identified, developed detailed rating anchors for each part and global severity and improvement ratings, reviewed the anchors with expert clinicians and established minimally clinically meaningful change for each symptom domain, and generated mock patient vignettes to test the reliability of the resulting scales and to standardize rater training. Frequently employed in clinical trials for neuropsychiatric disorders, the CGI scales were typically used in conjunction with disease-specific rating scales. When no disease-specific rating scale is available, the CGI scales can be adapted to reflect the specific symptom domains relevant to the disorder.