Potassium channel subunits encoded by several genes of the KCNQ family underlie 
the M-current. Specifically, KCNQ2 and KCNQ3 play a major role at most neuronal 
sites. Mutations in KCNQ2 or KCNQ3 that reduce the M-current are responsible for 
benign familial neonatal seizures, a rare autosomal dominant idiopathic epilepsy 
of the newborn. The aim of this study was to investigate a single family with 
benign familial neonatal seizures for mutations in KCNQ genes and to analyze the 
association of mutation type with disease prognosis. A family in which members 
in several generations had signs and symptoms compatible with a diagnosis of 
benign familial neonatal seizures had DNA testing with single-stranded 
conformation polymorphism analysis for various mutations known to cause benign 
familial neonatal seizures. A novel KCNQ2 mutation c.63-66delGGTG (p.K21fsX40), 
causing a framework shift and early chain termination, was identified in the 
affected family members. In all cases, there was complete remission of the 
seizures after the neonatal period. This KCNQ2 mutation has implications for 
diagnosis and prognosis of familial neonatal seizures. Its presence suggests a 
benign disease with good prognosis and its identification can spare patients and 
physicians the need for extensive investigations or prolonged therapy.