Dravet syndrome and genetic epilepsy with febrile seizures plus (GEFS+) can both 
arise due to mutations of SCN1A, the gene encoding the alpha 1 pore-forming 
subunit of the sodium channel. GEFS+ refers to a familial epilepsy syndrome 
where at least two family members have phenotypes that fit within the GEFS+ 
spectrum. The GEFS+ spectrum comprises a range of mild to severe phenotypes 
varying from classical febrile seizures to Dravet syndrome. Dravet syndrome is a 
severe infantile onset epilepsy syndrome with multiple seizure types, 
developmental slowing and poor outcome. More than 70% of patients with Dravet 
syndrome have mutations of SCN1A; these include both truncation and missense 
mutations. In contrast, only 10% of GEFS+ families have SCN1A mutations and 
these comprise missense mutations. GEFS+ has also been associated with mutations 
of genes encoding the sodium channel beta 1 subunit, SCN1B, and the GABA(A) 
receptor gamma 2 subunit, GABRG2. The phenotypic heterogeneity that is 
characteristic of GEFS+ families is likely to be due to modifier genes. 
Interpretation of the significance of a SCN1A missense mutation requires a 
thorough understanding of the phenotypes in the GEFS+ spectrum whereas a de novo 
truncation mutation is likely to be associated with a severe phenotype. Early 
recognition of Dravet syndrome is important as aggressive control of seizures 
may improve developmental outcome.