Karsten Haug

Mutations in CLCN2 encoding a voltage-gated chloride channel are associated with idiopathic generalized epilepsies.

Idiopathic generalized epilepsy (IGE) is an inherited neurological disorder affecting about 0.4% of the worlds population. Mutations in ten genes causing distinct forms of idiopathic epilepsy have been identified so far1,2,3,4,5,6,7, but the genetic basis of many IGE subtypes is still unknown. Here we report a gene associated with the four most common IGE subtypes: childhood and juvenile absence epilepsy (CAE and JAE), juvenile myoclonic epilepsy (JME), and epilepsy with grand mal seizures on awakening (EGMA; ref. 8). We identified three different heterozygous mutations in the chloride-channel gene CLCN2 in three unrelated families with IGE. These mutations result in (i) a premature stop codon (M200fsX231), (ii) an atypical splicing (del74–117) and (iii) a single amino-acid substitution (G715E). All mutations produce functional alterations that provide distinct explanations for their pathogenic phenotypes. M200fsX231 and del74–117 cause a loss of function of ClC-2 channels and are expected to lower the transmembrane chloride gradient essential for GABAergic inhibition. G715E alters voltage-dependent gating, which may cause membrane depolarization and hyperexcitability.

A novel SCN1A mutation associated with generalized epilepsy with febrile seizures plus-And prevalence of variants in patients with epilepsy

We recently described mutations of the neuronal sodium-channel alpha-subunit gene, SCN1A, on chromosome 2q24 in two families with generalized epilepsy with febrile seizures plus (GEFS+) type 2. To assess the contribution that SCN1A makes to other types of epilepsy, 226 patients with either juvenile myoclonic epilepsy, absence epilepsy, or febrile convulsions were screened by conformation-sensitive gel electrophoresis and manual sequencing of variants; the sample included 165 probands from multiplex families and 61 sporadic cases. The novel mutation W1204R was identified in a family with GEFS+. Seven other coding changes were observed; three of these are potential disease-causing mutations. Two common haplotypes, with frequencies of .67 and .33, were defined by five single-nucleotide polymorphisms (SNPs) spanning a 14-kb region of linkage disequilibrium. An SNP located 18 bp upstream of the splice-acceptor site for exon 3 was observed in 7 of the 226 patients but was not present in 185 controls, suggesting possible association with a disease mutation. This work has confirmed the role of SCN1A in GEFS+, by identification of a novel mutation in a previously undescribed family. Although a few candidate disease alleles were identified, the patient survey suggests that SCN1A is not a major contributor to idiopathic generalized epilepsy. The SCN1A haplotypes and SNPs identified here will be useful in future association and linkage studies.

In vivo activation of SMN in spinal muscular atrophy carriers and patients treated with valproate.

Spinal muscular atrophy results from loss of the survival motor neuron 1 (SMN1) gene and malfunction of the remaining SMN2. We investigated whether valproic acid can elevate human SMN expression in vivo.

CLCN2 variants in idiopathic generalized epilepsy

To the Editor: In 2003, we reported that mutations in CLCN2, the gene encoding the voltage-gated chloride channel ClC-2, are associated with the four major subtypes of idiopathic generalized epilepsy in three pedigrees with an apparent autosomal dominant mode of inheritance. We concluded that these mutations confer a major gene effect. The observed heterogeneity of the epileptic phenotypes prompted us to suggest that other, unknown genes might also be involved, in agreement with complex inheritance1. Re-examination of the families and the molecular genetic data by a neurologist and a geneticist who were not involved in the original study has now revealed major differences from the published data in two of the three published pedigrees (presented in Figs. 1a and 1b of the aforementioned publication1), which are described in detail below. All studies were approved by the Ethics Committee of the University of Bonn and informed consent was obtained from all subjects. In the previously published pedigree of Family 1 (ref. 1), the identified mutation cosegregates in an autosomal dominant manner in five affected family members. Three of these were indicated to be suffering from juvenile myoclonic epilepsy (JME) and one from epilepsy with grand mal (also known as generalized tonic-clonic) seizures on awakening (EGMA), and one was reported as showing generalized spike and wave discharges on an EEG without being clinically affected (Fig. 1a). The family was re-contacted and re-analyzed. This second evaluation revealed that only the index case had JME. She reported classical bilateral myoclonic jerks on awakening since the age of 17 and one generalized tonicclonic seizure in the morning that occurred when she was 18 years of age. She has been treated with valproate and has since remained seizure free for more than 15 years. EEG recordings were available only from the period when she was receiving valproate, and they did not show epileptic discharges. No other family members were reported as suffering from epileptic seizures, and the pedigree structure was found to be different from that initially described (Fig. 1b). We re-collected blood samples from nine available family members (Fig. 1b). The family structure was re-evaluated through molecular fingerprinting with 15 highly polymorphic STR markers and one sex-specific marker (Powerplex 16, Promega). The family structure obtained through the second recruitment proved to be correct. Re-sequencing of the CLCN2 gene revealed the published mutation c.597insG (p.M200fsX231) in three family members (the index patient, her unaffected sister and her unaffected father). Furthermore, three of the original DNA samples with the mutation proved to stem from one individual. The previously published pedigree of Family 2 (ref. 1) indicates an autosomal dominant form of epilepsy with eight affected members. The index case was reported as suffering from childhood absence epilepsy (CAE), his sister as showing generalized spike and wave discharges on the EEG without being clinically affected, five other family members as suffering from EGMA, and the deceased great-grandfather of the index case was reported to have had unclassifiable epileptic seizures (Fig. 1c). The family was re-contacted and the clinical phenotypes were re-evaluated using information obtained from the parents of the index I

The voltage-gated sodium channel beta2-subunit gene and idiopathic generalized epilepsy.

Recent identification of ion channel gene mutations in Mendelian epilepsies suggests that genetically driven neuronal hyperexcitability plays an important role in epileptogenesis. In this study, we tested the hypothesis that genetic variation in the human SCN2B gene confers liability to common subtypes of idiopathic generalized epilepsies (IGE). A systematic search for mutations was performed in 92 IGE patients. We detected a novel single nucleotide polymorphism (SNP), however, allele frequencies did not differ between IGE patients and controls (chi2 = 0.19, df = 1, p = 0.744). Furthermore, a missense mutation in codon 209 (Asn209Pro) was identified in one patient, but was found to be absent in an affected sibling of the index patient. Thus, our results do not suggest a major role of the SCN2B gene in the etiology of common IGE subtypes.

No evidence for association between the KCNQ3 gene and susceptibility to idiopathic generalized epilepsy

Idiopathic generalized epilepsy (IGE) comprises a heterogeneous group of disorders, in which a high genetic predisposition and a complex mode of inheritance have been suggested. Recent identification of ion channel gene mutations in Mendelian epileptic disorders suggests genetically driven neuronal hyperexcitability as one important factor in epileptogenesis. Mutations in two neuronal voltage-gated potassium channel genes (KCNQ2 and KCNQ3) have already been shown to cause epilepsy (BFNC), and we now tested the hypothesis that genetic variation in the KCNQ3 gene confers liability to common IGE subtypes. Length variation of two intragenic polymorphic markers (D8S558 and D8S1835) were therefore assessed in 71 nuclear families ascertained for an affected child. However, the transmission-disequilibrium-test did not show significant differences between the transmitted and non-transmitted parental alleles. Thus, our findings do not provide evidence that genetic variation in the KCNQ3 gene exerts a relevant effect in the etiology of common IGE subtypes.

Familial Sotos syndrome caused by a novel missense mutation, C2175S, in NSD1 and associated with normal intelligence, insulin dependent diabetes, bronchial asthma, and lipedema.

We report a familial Sotos syndrome in two children, boy and girl, aged 17 and 8 years, and in their 44 year old mother, who displayed normal intelligence at adult age, but suffered from insulin dependent diabetes mellitus, bronchial asthma, and severe lipedema. The underlying missense mutation, C2175S, occurred in a conserved segment of the NSD1 gene. Our findings confirm that familial cases of SS are more likely to carry missense mutations. This case report may prove useful to avoid underestimation of the recurrence rate of SS, and to demonstrate that the developmental delay may normalize, enabling an independent life and having an own family.

Familial fatal fetal cardiomyopathy with isolated myocardial calcifications: a new syndrome?

We describe three male sib fetuses with isolated myocardial calcifications resulting in intrauterine fetal death (IUFD) as early as the second trimester. No evidence for an underlying mitochondrial cytopathy, dystrophinopathy or myopathy was found. There were no signs of inflammation or a metabolic disorder, and the mother had no prenatal exposure of teratogenic drugs. Furthermore, no mutation in the Barth syndrome gene (G4.5) could be detected. Because isolated calcification of the heart and IUFD are not typical of any previously described inherited cardiomyopathy, it may represent a new familial fetal cardiomyopathy.

Association analysis between a regulatory-promoter polymorphism of the human monoamine oxidase A gene and idiopathic generalized epilepsy

Monoaminergic neurotransmission plays an important role in the regulation of neuronal network excitability and seizure activity. Therapeutic inhibition of the mitochondrial enzyme monoamine oxidase A (MAO-A), which is involved in the degradation and inactivation of monoaminergic neurotransmitters, has been shown to confer a potent anticonvulsant effect. These and other findings suggest a possible role of the X-linked MAO-A gene in epileptogenesis. Therefore, our study was designed to test for an association between a novel MAO-A gene promoter polymorphism and common subtypes of idiopathic generalized epilepsy (IGE). The length of a 30-bp repetitive sequence approximately 1.2 kb upstream of the ATG initiation codon was assessed in 126 patients with juvenile myoclonic epilepsy (JME), 122 patients with idiopathic absence epilepsy (IAE), and 248 healthy controls of German descent. Both sexes were analyzed separately. Although we observed a trend towards a lower number of heterozygotes carrying the 3 and 4 copy alleles in female IAE patients (chi2 = 3.813, df = 1, P = 0.053), allele frequencies did not deviate significantly between patients and controls. Thus, our results do not provide evidence for a contribution of the functional MAO-A gene promoter polymorphism to the pathogenesis of common IGE subtypes.