A potassium channel mutation in neonatal human epilepsy.

Benign familial neonatal convulsions (BFNC) is an autosomal dominant epilepsy of infancy, with loci mapped to human chromosomes 20q13.3 and 8q24. By positional cloning, a potassium channel gene (KCNQ2) located on 20q13.3 was isolated and found to be expressed in brain. Expression of KCNQ2 in frog (Xenopus laevis) oocytes led to potassium-selective currents that activated slowly with depolarization. In a large pedigree with BFNC, a five-base pair insertion would delete more than 300 amino acids from the KCNQ2 carboxyl terminus. Expression of the mutant channel did not yield measurable currents. Thus, impairment of potassium-dependent repolarization is likely to cause this age-specific epileptic syndrome.

The new voltage gated potassium channel KCNQ5 and neonatal convulsions.

In 1998, mutations in the voltage gated potassium channel gene KCNQ2 were found to be the main cause underlying the autosomal dominant inherited syndrome of benign familial neonatal convulsions (BFNC). In one BFNC family a mutation was found in an homologous gene, KCNQ3. We have now identified another brain-expressed member of this ion channel subfamily, KCNQ5, which maps to chromosome 6q14. On the genomic level KCNQ5 is composed of 14 exons, which are coding for 897 amino acid residues. Mutation analysis made KCNQ5 unlikely as a candidate gene for benign neonatal convulsions in patients with a positive family history for neonatal or early infantile seizures, but without mutations in the KCNQ2 or KCNQ3 genes.

The voltage gated potassium channel KCNQ2 and idiopathic generalized epilepsy.

Mutations in the voltage gated potassium channel gene KCNQ2 and the homologous gene KCNQ3 have been found to cause a rare monogenic subtype of idiopathic generalized epilepsy, the benign familial neonatal convulsions. Recently, the heteromeric KCNQ2/KCNQ3 channel was found to contribute to the native M-current, one of the most important regulators of neuronal excitability. By performing a systematic mutation scan of the coding region and an association study involving a frequent Thr752Asn substitution polymorphism, we, therefore, investigated whether allelic variation of the KCNQ2 gene confers susceptibility to common subtypes of idiopathic generalized epilepsy. Our results do not provide evidence that allelic variation of the KCNQ2 gene contributes a common and relevant effect to the pathogenesis of common subtypes of idiopathic generalized epilepsy.

Semiquantitative expression analysis of ephrine-receptor tyrosine kinase mRNA's in a rat model of traumatic brain injury.

The molecular mechanisms involved in recovery of function of the central nervous system (CNS) after injury to the brain are incompletely understood. Here the expression of ephrine (Eph) kinases following traumatic brain injury (subdural haematoma) was analysed in order to find out whether these developmentally regulated genes may be involved in tissue remodelling after brain damage. mRNA was isolated from ipsilateral cortices 7, 18, and 28 days after surgery and semiquantitative reverse transcription-polymerase chain reaction was performed. Most Eph kinases did not show significant regulation at gene expression level during the time course of recovery from acute brain injury but there is some evidence that mRNA of EphB1 might be slightly upregulated.

Structural and mutational analysis of KCNQ2, the major gene locus for benign familial neonatal convulsions.

Mutations in the voltage-gated potassium channel gene KCNQ2 on chromosome 20q13.3 are responsible for benign familial neonatal convulsions (BFNC), a rare monogenic idiopathic epilepsy. Here we report the determination of the detailed genomic structure of KCNQ2, and use of this information in mutational analysis. There are at least 18 exons, occupying more than 50 kb of genomic DNA. Several formerly unknown polymorphisms and splice variants as well as a new single base pair deletion mutation of unusual localization are described. In addition to facilitating more effective mutation detection among BFNC patients, the results presented here provide the basis for analysing the role of KCNQ2 in other types of epilepsy.

A KCNQ2 splice site mutation causing benign neonatal convulsions in a Scottish family.

Benign familial neonatal convulsions (BFNC) are one of the rare idiopathic epilepsies with autosomal dominant mode of inheritance. Two voltage-gated potassium channels, KCNQ2 on chromosome 20q13.3 and KCNQ3 on 8q24, have been recently identified as the genes responsible for BFNC. Here we describe a large family with BFNC in which we found a previously undescribed mutation in the KCNQ2 gene. A 1187(+2)T/G nucleotide exchange affects the conserved donor splice site motif in intron 9. This mutation can be predicted to give rise to aberrant splicing of the primary transcript. There was a wide range of clinical manifestations in this family. An unusual clinical feature is the occurrence of partial seizures in later life with corresponding focal neurological deficits.

A reduced K+ current due to a novel mutation in KCNQ2 causes neonatal convulsions.

Benign familial neonatal convulsions (BFNC) is a rare dominantly inherited epileptic syndrome characterized by frequent brief seizures within the first days of life. The disease is caused by mutations in one of two recently identified voltage-gated potassium channel genes, KCNQ2 or KCNQ3. Here, we describe a four-generation BFNC family carrying a novel mutation within the distal, unconserved C-terminal domain of KCNQ2, a 1-bp deletion, 2513delG, in codon 838 predicting substitution of the last seven and extension by another 56 amino acids. Three family members suffering from febrile but not from neonatal convulsions do not carry the mutation, confirming that febrile convulsions and BFNC are of different pathogenesis. Functional expression of the mutant channel in Xenopus oocytes revealed a reduction of the potassium current to 5% of the wild-type current, but the voltage sensitivity and kinetics were not significantly changed. To find out whether the loss of the last seven amino acids or the C-terminal extension because of 2513delG causes the phenotype, a second, artificial mutation was constructed yielding a stop codon at position 838. This truncation increased the potassium current by twofold compared with the wild type, indicating that the pathological extension produces the phenotype, and suggesting an important role of the distal, unconserved C-terminal domain of this channel. Our results indicate that BFNC is caused by a decreased potassium current impairing repolarization of the neuronal cell membrane, which results in hyperexcitability of the central nervous system.