In patient P27, methylation-specific MLPA confirmed deletion of maternal alleles in the 15q11.2 region, which contains SNRPN, UBE3A, and GABRB3. The phenotype and distinctive EEG pattern of patient P27 were compatible with Angelman syndrome, which is prolonged runs of high amplitude rhythmic 2–3 Hz activity predominantly over the frontal regions with superimposed interictal epileptiform discharges and high amplitude rhythmic 4–6 Hz activity prominent in the occipital regions with spikes. The gene discussed is GABRB3; the disease is Angelman syndrome.