Dravet syndrome is a severe form of epileptic encephalopathy characterized by 
early onset epileptic seizures followed by ataxia and cognitive decline. 
Approximately 80% of patients with Dravet syndrome have been associated with 
heterozygous mutations in SCN1A gene encoding voltage-gated sodium channel 
(VGSC) α(I) subunit, whereas a homozygous mutation (p.Arg125Cys) of SCN1B gene 
encoding VGSC β(I) subunit was recently described in a patient with Dravet 
syndrome. To further examine the involvement of homozygous SCN1B mutations in 
the etiology of Dravet syndrome, we performed mutational analyses on SCN1B in 
286 patients with epileptic disorders, including 67 patients with Dravet 
syndrome who have been negative for SCN1A and SCN2A mutations. In the cohort, we 
found one additional homozygous mutation (p.Ile106Phe) in a patient with Dravet 
syndrome. The identified homozygous SCN1B mutations indicate that SCN1B is an 
etiologic candidate underlying Dravet syndrome.