Twenty-six patients with Angelman syndrome (AS), of which 19 had 15ql 1-13 maternal deletion, were studied and followed at the University of San Paulo, Brazil, with particular reference to the prevalence and type of epilepsy and its response to antiepileptic drugs. Epilepsy occurred in 22 patients (85%), 19 with deletion and 3 without positive genetic confirmation. All 19 patients with deletion had generalized seizures, and 10 (53%) had partial seizures. Yideo-EEG uncovered atypical absence and subtle myoclonic seizures, often missed by parents; it also recorded nonconvulsive status that is sometimes prolonged and associated with cognitive decline in 7. Mean age at onset of seizures was 1 year 1 month, and in 18 patients, epilepsy preceded the clinical diagnosis of AS. Five (26%) had their first seizure with fever, and 10 (53%) had epilepsy aggravated by fever. Sixteen (84%) had status epilepticus, associated with hyperthermia in 7. Valproic acid, alone or in combination with phenobarbital or clonazepam, improved seizure control while carbamazepine, oxcarbazepine, and vigabatrin caused aggravation of seizures. Refractory seizures occurred in 16 (84%) during infancy and early childhood, but seizure frequency decreased at a mean age of 5.3 years. Improvement in seizure frequency and severity continued through late childhood and puberty. 
COMMENT. Angelman syndrome is characterized by developmental delay, severe mental retardation, paroxysmal laughter, ataxia associated with hand flapping, seizures, and stereotyped jerky movements, regarded as cortical myoclonus . Physical signs include microcephaly, prominent jaw, wide mouth, pointed chin, and hypopigmentation. Seizures are mainly generalized, frequently partial, atypical absence, myoclonic, sometimes included as a cause of West, or Lennox-Gastaut syndromes, and, as shown in the above study, often febrile in type.
The typical interictal EEG abnormality shows rhythmic slow waves at 4-6 Hz and runs of 2-3 Hz slow spike-wave complexes anteriorly. Eye closure is accompanied by spikes and 2-4 Hz slow waves posteriorly [3, 4]. Status epilepticus is a frequent complication, sometimes precipitated by hyperthermia, and often recurrent. Age-related improvement in seizure frequency and severity is an additional characteristic.
The diagnosis of AS should be considered in infants with developmental delay and generalized cryptogenic seizures resistant to medication. Diagnosis is confirmed in 85% by genetic testing and deletion of chromosome 15ql 1-13. In rare cases, other genetic mechanisms have been uncovered, and in 15% of cases, diagnosis is made on clinical and EEG findings alone. Where possible, the genetic cause should be determined as a prelude to family counseling.