Classic Dravet syndrome is also termed severe myoclonic epilepsy of infancy (SMEI). There are subtle phenotypic variants of Dravet which may have all the features of the syndrome except one, such as without myoclonic seizures, onset in the second year or without generalized spike and wave on EEG. These have been termed borderline variants of SMEI. Rather than ascribing multiple different names to marginally different phenotypes, the term Dravet syndrome is now preferred to describe the group of severe infantile onset epilepsies (OMIM #607208, #182389, #604403) associated with mutations in SCN1A (OMIM *182389).
SCN1A-related seizure disorders can be inherited in an autosomal dominant manner but most are due to de novo mutations. SCN1A testing can be done through bi-directional DNA sequencing and multiplex ligation-dependent probe amplification (MLPA) for:
1) individuals with electroclinical phenotype of Dravet Syndrome or clinical sub-types – several seizure types in one individual with onset in infancy, refractory to medication and with generalised spike and wave on EEG, or
2) infants less than 1 year old with 2 or more prolonged hemiclonic febrile seizures in early infancy.
Disclaimer: This summary is based on a UK Genetic Testing Network (UKGTN) approved Gene Dossier application.