Mutations in SCN1A gene, encoding the voltage-gated sodium channel α1-subunit, 
are found to be associated with severe myoclonic epilepsy in infancy or Dravet 
syndrome (DS), but only rarely with the myoclonic astatic epilepsy (MAE, or 
Doose syndrome). We report on two patients with SCN1A mutations and severe 
epilepsy within the spectrum of generalized epilepsy with febrile seizures plus 
syndrome (GEFS+), the phenotypes being consistent with DS and MAE, respectively. 
Analysis of SCN1A revealed a heterozygous de novo frameshift mutation 
(c.4205_4208delGAAA) in the patient with DS, and a recurrent missense mutation 
(c.3521C>G) in that suffering from MAE. The missense mutation has been reported 
in patients with neurological diseases of various manifestations, which suggests 
that this variability is likely to result from the modifying effects of other 
genetic or environmental factors. DS phenotype has been mainly found associated 
with truncation mutations, while predominantly missense mutations and very few 
prematurely terminating substitutions have been reported in GEFS+ patients.