Mutations in the SCN1A gene are found in up to 80% of individuals with severe 
myoclonic epilepsy of infancy (SMEI), and mutations in KCNQ2 and KCNQ3 were 
identified in benign familial neonatal convulsions (BFNC) as well as in single 
families with Rolandic epilepsy (RE) and idiopathic generalized epilepsies 
(IGE). This paper summarizes recent findings concerning sodium (SCN1A) and 
potassium channel (KCNQ2 and KCNQ3) dysfunctions in the pathogenesis of rare and 
common idiopathic epilepsies (IE). SMEI, severe idiopathic generalized epilepsy 
of infancy (SIGEI), and myoclonic-astatic epilepsy (MAE) are rare IE. Because of 
some semeiologic overlap, a comparative analysis of the SCN1A gene performed in 
20 patients with MAE and in 18 with SIGEI. This revealed mutations in three 
subjects with SIGEI only. Since BFNC are over-represented in families with RE, a 
mutational analysis was performed in 58 families with RE with and without BNFC. 
This revealed functionally relevant mutations in two index cases with BNFC, and 
three missense mutations (one resulting in a significantly reduced potassium 
current amplitude) in three patients with RE, but without BNFC. One KCNQ3 
missense variant was also detected in eight out of 455 IGE patients but not in 
454 controls, and a silent KCNQ2-SNP was found over-represented in both epilepsy 
samples. These findings confirm that mutations in the SCN1A gene are mainly 
involved in the pathogenesis of SMEI, rarely in that of SIGEI, and are commonly 
not found in patients with MAE. They also demonstrate that sequence variations 
of the KCNQ2 and KCNQ3 genes may contribute to the etiology of common IE 
syndromes.