Angelman and Rett syndrome are neurodevelopmental disorders with significant phenotypic overlap. Classic Rett syndrome is a progressive disorder characterized by acquired microcephaly, loss of purposeful hand movements, and autistic behaviors, following a period of normal growth and development. Additional features include scoliosis, epilepsy, poor growth, and irregular breathing. There is broad clinical variability in the severity of Rett syndrome, including variants of Rett syndrome which may be associated with atypical features compared to the classic phenotype. Classic Rett syndrome primarily affects females.
Angelman syndrome is characterized by functionally severe developmental delay or intellectual disability, movement or balance disorders of variable severity, behavioral uniqueness exemplified by apparent happy demeanor (frequent laughing/smiling) and easy excitability, and severe speech impairment. Other characteristics noted in over 80% of patients include microcephaly, seizures, and a specific, abnormal EEG pattern. Patients may also exhibit wide mouths with unusual tongue/mouthing behaviors, hypopigmentation, and abnormal sleep-wake cycles. Older patients may experience obesity.