Editor—Angelman syndrome (AS) is a genetic disorder characterised by severe mental retardation, no speech, a wide based gait with arms flexed at the elbows, resembling a newly walking toddler, paroxysms of laughter, characteristic facial features, epileptic seizures, and typical EEG abnormalities.1-3 The clinical diagnosis can be confirmed by chromosomal studies or molecular analysis in about 80% of patients, in most of whom a maternally inherited deletion of chromosome 15q11-13 is found. Rarely, other abnormalities are found, such as an abnormal methylation pattern of the 15q11-13 region of the maternal chromosome, paternal uniparental disomy (UPD), or imprinting centre mutations. In the remaining 20% no abnormality can be identified. Recently, two groups described mutations in the E6-AP ubiquitin protein ligase gene (UBE3A), located within the 15q11-13 region,4 5 suggesting that deficiency of theUBE3A locus could cause AS.

We previously …