Benign familial neonatal convulsions (BFNC) resulting from mutation of the KCNQ2 voltage sensor.

:Benign familial neonatal convulsions (BFNC) is a rare autosomal inherited epilepsy. We studied the KCNQ2 coding region in a large, four-generation, Italian family with BFNC. A missense mutation C686T predicting the change of one of the innermost arginine (R214W) of the key functional voltage sensor (S4 helix), has been found in all affected members. This substitution probably reduces the movement of the voltage sensor that precedes channel opening during voltage-dependent activation. Several mutations affecting the trans-membrane domain and the pore region of the K+ channels belonging to the KQT-like family have been described in some human diseases associated with altered regulation of cellular excitability (ie BFNC, some LQT syndromes and DFNA2). R214W represents the first mutation involving the region of the voltage sensor.

Miraglia del Giudice E ，Coppola G ，Scuccimarra G ，Cirillo G ，Bellini G ，Pascotto A ... -  《EUROPEAN JOURNAL OF HUMAN GENETICS》

A novel missense mutation (N258S) in the KCNQ2 gene in a Turkish family afflicted with benign familial neonatal convulsions (BFNC).

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.

Yalçin O ，Cağlayan SH ，Saltik S ，Cokar O ，Ağan K ，Dervent A ，Steinlein OK ... -  《TURKISH JOURNAL OF PEDIATRICS》

A novel potassium channel gene, KCNQ2, is mutated in an inherited epilepsy of newborns.

Idiopathic generalized epilepsies account for about 40% of epilepsy up to age 40 and commonly have a genetic basis. One type is benign familial neonatal convulsions (BFNC), a dominantly inherited disorder of newborns. We have identified a sub-microscopic deletion of chromosome 20q13.3 that co-segregates with seizures in a BFNC family. Characterization of cDNAs spanning the deleted region identified one encoding a novel voltage-gated potassium channel, KCNQ2, which belongs to a new KQT-like class of potassium channels. Five other BFNC probands were shown to have KCNQ2 mutations, including two transmembrane missense mutations, two frameshifts and one splice-site mutation. This finding in BFNC provides additional evidence that defects in potassium channels are involved in the mammalian epilepsy phenotype.

Singh NA ，Charlier C ，Stauffer D ，DuPont BR ，Leach RJ ，Melis R ，Ronen GM ，Bjerre I ，Quattlebaum T ，Murphy JV ，McHarg ML ，Gagnon D ，Rosales TO ，Peiffer A ，Anderson VE ，Leppert M ... -  《NATURE GENETICS》

A pore mutation in a novel KQT-like potassium channel gene in an idiopathic epilepsy family.

Epileptic disorders affect about 20-40 million people worldwide, and 40% of these are idiopathic generalized epilepsies (IGEs; ref. 1). Most of the IGEs that are inherited are complex, multigenic diseases. To address basic mechanisms for epilepsies, we have focused on one well-defined class of IGEs with an autosomal-dominant mode of inheritance: the benign familial neonatal convulsions (BFNC; refs 2,3). Genetic heterogeneity of BFNC has been observed. Two loci, EBN1 and EBN2, have been mapped by linkage analysis to chromosome 20q13 (refs 5,6) and chromosome 8q24 (refs 7,8), respectively. By positional cloning, we recently identified the gene for EBN1 as KCNQ2 (ref. 9). This gene, a voltage-gated potassium channel, based on homology, is a member of the KQT-like family. Here we describe an additional member, KCNQ3. We mapped this new gene to chromosome 8, between markers D8S256 and D8S284 on a radiation hybrid map. We screened KCNQ3 for mutations in the large BFNC family previously linked to chromosome 8q24 in the same marker interval. We found a missense mutation in the critical pore region in perfect co-segregation with the BFNC phenotype. The same conserved amino acid is also mutated in KVLQT1 (KCNQ1) in an LQT patient. KCNQ2, KCNQ3 and undiscovered genes of the same family of K+ channels are strong candidates for other IGEs.

Charlier C ，Singh NA ，Ryan SG ，Lewis TB ，Reus BE ，Leach RJ ，Leppert M ... -  《NATURE GENETICS》

KCNQ2 and KCNQ3 potassium channel genes in benign familial neonatal convulsions: expansion of the functional and mutation spectrum.

Benign familial neonatal convulsions (BFNC) is a rare autosomal dominant generalized epilepsy of the newborn infant. Seizures occur repeatedly in the first days of life and remit by approximately 4 months of age. Previously our laboratory cloned two novel potassium channel genes, KCNQ2 and KCNQ3, and showed that they are mutated in patients with BFNC. In this report, we characterize the breakpoints of a previously reported interstitial deletion in the KCNQ2 gene and show that only KCNQ2 is deleted. We identify 11 novel mutations in KCNQ2 and one novel mutation in the KCNQ3 potassium channel genes. In one family, the phenotype extends beyond neonatal seizures and includes rolandic seizures, and a subset of families has onset of seizures in infancy. In the Xenopus oocyte expression system, we characterize five KCNQ2 and one KCNQ3 disease-causing mutations. These mutations cause a variable loss of function, and selective effects on the biophysical properties of KCNQ2/KCNQ3 heteromultimeric channels. We report here the first dominant negative mutation in KCNQ2 that has a phenotype of neonatal seizures without permanent clinical CNS impairment.

Singh NA ，Westenskow P ，Charlier C ，Pappas C ，Leslie J ，Dillon J ，Anderson VE ，Sanguinetti MC ，Leppert MF ，BFNC Physician Consortium ... -  《BRAIN》