Benign familial neonatal convulsions (BFNC) is a rare monogenic subtype of 
idiopathic epilepsy exhibiting autosomal dominant mode of inheritance. The 
disease is caused by mutations in the two homologous genes KCNQ2 and KCNQ3 that 
encode the subunits of the voltage-gated potassium channel. Most KCNQ2 mutations 
are found in the pore region and the cytoplasmic C domain. These mutations are 
either deletions/insertions that result in frameshift or truncation of the 
protein product, splice-site variants or missense mutations. This study reveals 
a novel missense mutation (N258S) in the KCNQ2 gene between the S5 domain and 
the pore of the potassium channel in two BFNC patients in a Turkish family. The 
absence of the mutation both in the healthy members of the family and in a 
control group, and the lack of any other change in the KCNQ2 gene of the 
patients indicate that N258S substitution is a pathogenic mutation leading to 
epileptic seizures in this family.