This observational research study is designed to learn more about how the brain processes sound in individuals with Rett syndrome. Participants will complete a noninvasive electroencephalogram (EEG) recording while listening to simple sounds through headphones. In addition, parents or caregivers will complete questionnaires and an interview about the participant's symptoms, communication abilities, daily functioning and overall health. The information collected from this study may help researchers better understand brain activity patterns and clinical features associated with Rett syndrome and support future research efforts.