Angelman Syndrome EEG Notched Delta

A 4-year-old girl with severe global developmental delay, absent speech, ataxic gait, and frequent inappropriate laughter is evaluated in the pediatric neurology clinic. She has microcephaly, a wide mouth with prognathia, and a happy demeanor with easy excitability. Genetic testing confirms maternal UBE3A deletion (15q11-q13). An EEG is performed as part of the diagnostic workup. The pattern marked **A** in the diagram—high-amplitude 2-3 Hz delta with intermittent notched waves and posterior spike-slow-wave activity—is a highly distinctive finding in this condition. Which of the following best describes the clinical significance of this EEG pattern in the context of this diagnosis?