OBJECTIVESevere myoclonic epilepsy of infancy (SMEI), or Dravet syndrome, is a severe epileptic encephalopathy. This study aimed to investigate the clinical features and genetic diagnosis of SMEI.

METHODSThe electroclinical data and the mutation of SCN1A gene in 13 children with SMEI were analyzed.

RESULTSOf the 13 children, 10 were males and 3 were females. Eight of them had family history of febrile seizures. The average age of seizure onset was 5.6 months, with a range of 2 to 9 months. The initial seizure was a febrile seizure in 9 patients (69%). Generalized or hemiclonic seizures were often triggered by fever. Eight patients had a history of febrile status. Afebrile seizures occurred from 2 months to 21 months of age. All patients went on to develop multiple seizure types. Generalized tonic clonus seizures (GTCS) were found in 11, partial seizures in 12, atypical absence in 10. Myoclonic seizures were presented in all patients. Twelve patients had 3 or more seizure types. Seizures of all patients had a characteristic of temperature sensitivity. The precipitating factors included fever, hot bath and vaccination. Nine patients (69%) had a history of status epilepticus. Delay in mental development was present in 11 cases, ataxia in 5 and pyramidal sign in 2. EEG was normal in most patients in the first year of life, followed by generalized, focal and multifocal discharges. Brain MRI was abnormal in 2 cases. Seizures were not completely controlled in all patients. Carbamazepine and lamotrigine aggravated seizures in some patients. SCN1A gene mutation was found in 10 cases, including seven missense mutations, two nonsense mutations and one frame shift mutation.

CONCLUSIONThe clinical features of SMEI were seizure onset within one year of age, first event is often a febrile seizure; multiple seizure types and mental delay occurred after the second year of life; seizures have a characteristic of temperature sensitivity; EEG was normal in the first year of life, followed by generalized, focal or multifocal discharges; early diagnosis by testing SCN1A mutation guides selection of antiepileptic drugs.