The LGI1 gene involved in lateral temporal lobe epilepsy belongs to a new subfamily of leucine-rich repeat proteins

Oligodendrocyte-derived LGI3 and its receptor ADAM23 organize juxtaparanodal Kv1 channel clustering for short-term synaptic plasticity

Neurodevelopmental disorders, such as intellectual disability (ID), epilepsy, and autism, involve altered synaptic transmission and plasticity. Functional characterization of their associated genes is vital for understanding physio-pathological brain functions. LGI3 is a recently recognized ID-associated gene encoding a secretory protein related to an epilepsy-gene product, LGI1. Here, we find that LGI3 is uniquely secreted from oligodendrocytes in the brain and enriched at juxtaparanodes of myelinated axons, forming nanoscale subclusters. Proteomic analysis using epitope-tagged Lgi3 knockin mice shows that LGI3 uses ADAM23 as a receptor and selectively co-assembles with Kv1 channels. A lack of Lgi3 in mice disrupts juxtaparanodal clustering of ADAM23 and Kv1 channels and suppresses Kv1-channel-mediated short-term synaptic plasticity. Collectively, this study identifies an extracellular organizer of juxtaparanodal Kv1 channel clustering for finely tuned synaptic transmission. Given the defective secretion of the LGI3 missense variant, we propose a molecular pathway, the juxtaparanodal LGI3-ADAM23-Kv1 channel, for understanding neurodevelopmental disorders.

The environmental carcinogen benzo[a]pyrene regulates epigenetic reprogramming and metabolic rewiring in a two-stage mouse skin carcinogenesis model

Non-melanoma skin cancer (NMSC) is the most common cancer in the world. Environmental exposure to carcinogens is one of the major causes of NMSC initiation and progression. In the current study, we utilized a two-stage skin carcinogenesis mouse model generated by sequential exposure to cancer-initiating agent benzo[a]pyrene (BaP) and promoting agent 12-O-tetradecanoylphorbol-13-acetate (TPA), to study epigenetic, transcriptomic and metabolic changes at different stages during the development of NMSC. BaP/TPA caused significant alterations in DNA methylation and gene expression profiles in skin carcinogenesis, as evidenced by DNA-seq and RNA-seq analysis. Correlation analysis between differentially expressed genes and differentially methylated regions found that the mRNA expression of oncogenes leucine rich repeat LGI family member 2 (Lgi2), kallikrein-related peptidase 13 (Klk13) and SRY-Box transcription factor (Sox5) are correlated with the promoter CpG methylation status, indicating BaP/TPA regulates these oncogenes through regulating their promoter methylation at different stages of NMSC. Pathway analysis identified that the modulation of macrophage-stimulating protein-recepteur d'origine nantais and high-mobility group box 1 signaling pathways, superpathway of melatonin degradation, melatonin degradation 1, sirtuin signaling and actin cytoskeleton signaling pathways are associated with the development of NMSC. The metabolomic study showed BaP/TPA regulated cancer-associated metabolisms like pyrimidine and amino acid metabolisms/metabolites and epigenetic-associated metabolites, such as S-adenosylmethionine, methionine and 5-methylcytosine, indicating a critical role in carcinogen-mediated metabolic reprogramming and its consequences on cancer development. Altogether, this study provides novel insights integrating methylomic, transcriptomic and metabolic-signaling pathways that could benefit future skin cancer treatment and interception studies.

The LGI1 protein: molecular structure, physiological functions and disruption-related seizures

Leucine-rich, glioma inactivated 1 (LGI1) is a secreted glycoprotein, mainly expressed in the brain, and involved in central nervous system development and physiology. Mutations of LGI1 have been linked to autosomal dominant lateral temporal lobe epilepsy (ADLTE). Recently auto-antibodies against LGI1 have been described as the basis for an autoimmune encephalitis, associated with specific motor and limbic epileptic seizures. It is the second most common cause of autoimmune encephalitis. This review presents details on the molecular structure, expression and physiological functions of LGI1, and examines how their disruption underlies human pathologies. Knock-down of LGI1 in rodents reveals that this protein is necessary for normal brain development. In mature brains, LGI1 is associated with Kv1 channels and AMPA receptors, via domain-specific interaction with membrane anchoring proteins and contributes to regulation of the expression and function of these channels. Loss of function, due to mutations or autoantibodies, of this key protein in the control of neuronal activity is a common feature in the genesis of epileptic seizures in ADLTE and anti-LGI1 autoimmune encephalitis.

Leucine rich repeat LGI family member 3: Integrative analyses reveal its prognostic association with non-small cell lung cancer

Leucine rich repeat LGI family member 3 (LGI3) is a member of the LGI protein family. Our previous studies reported that LGI3 was expressed in adipose tissues, brain and skin, where it served roles as a multifunctional cytokine and pro-inflammatory adipokine. It was hypothesized that LGI3 may be involved in cytokine networks in cancer. The present study aimed to analyze differentially expressed genes in non-small cell lung cancer (NSCLC) tissues and NSCLC cohort data, to evaluate the prognostic role of LGI3. Expression microarray and NSCLC cohort data were statistically analyzed by bioinformatic methods, and protein-protein interactions, functional enrichment and pathway, gene coexpression network (GCN) and prognostic association analyses were performed. The results demonstrated that the expression levels of LGI3 and its receptor a disintegrin and metalloproteinase domain-containing protein 22 were significantly decreased in NSCLC tissues. A total of two upregulated genes and 11 downregulated genes in NSCLC tissues were identified as LGI3-regulated genes. Protein-protein interaction network analysis demonstrated that all LGI3-regulated genes that were altered in NSCLC were involved in a protein-protein interaction network cluster. Functional enrichment, Kyoto Encyclopedia of Genes and Genomes pathway and GCN analyses demonstrated the association of these genes with the immune and inflammatory responses, angiogenesis, the tumor necrosis factor pathway, and chemokine and peroxisome proliferator-activated receptor signaling pathways. Analysis of NSCLC cohorts revealed that low expression levels of LGI3 was significantly associated with poor prognosis of NSCLC. Analysis of the somatic mutations of the LGI3 gene in NSCLC revealed that the amino acid residues altered in NSCLC included two single nucleotide polymorphism sites and three phylogenetically coevolved amino acid residues. Taken together, these results suggest that LGI3 may be a potential prognostic marker of NSCLC.

Enhanced synaptic plasticity and spatial memory in female but not male FLRT2-haplodeficient mice

The Fibronectin Leucine-Rich Transmembrane protein 2 (FLRT2) has been implicated in several hormone -and sex-dependent physiological and pathological processes (including chondrogenesis, menarche and breast cancer); is known to regulate developmental synapses formation, and is expressed in the hippocampus, a brain structure central for learning and memory. However, the role of FLRT2 in the adult hippocampus and its relevance in sex-dependent brain functions remains unknown. We here used adult single-allele FLRT2 knockout (FLRT2+/-) mice and behavioral, electrophysiological, and molecular/biological assays to examine the effects of FLRT2 haplodeficiency on synaptic plasticity and hippocampus-dependent learning and memory. Female and male FLRT2+/- mice presented morphological features (including body masses, brain shapes/weights, and brain macroscopic cytoarchitectonic organization), indistinguishable from their wild type counterparts. However, in vivo examinations unveiled enhanced hippocampus-dependent spatial memory recall in female FLRT2+/- animals, concomitant with augmented hippocampal synaptic plasticity and decreased levels of the glutamate transporter EAAT2 and beta estrogen receptors. In contrast, male FLRT2+/- animals exhibited deficient memory recall and decreased alpha estrogen receptor levels. These observations propose that FLRT2 can regulate memory functions in the adulthood in a sex-specific manner and might thus contribute to further research on the mechanisms linking sexual dimorphism and cognition.

Molecular cloning and characterization of the family of feline leucine-rich glioma-inactivated (LGI) genes, and mutational analysis in familial spontaneous epileptic cats

BACKGROUND

Leucine-rich glioma-inactivated (LGI) proteins play a critical role in synaptic transmission. Dysfunction of these genes and encoded proteins is associated with neurological disorders such as genetic epilepsy or autoimmune limbic encephalitis in animals and human. Familial spontaneous epileptic cats (FSECs) are the only feline strain and animal model of familial temporal lobe epilepsy. The seizure semiology of FSECs comprises recurrent limbic seizures with or without evolution into generalized epileptic seizures, while cats with antibodies against voltage-gated potassium channel complexed/LGI1 show limbic encephalitis and recurrent limbic seizures. However, it remains unclear whether the genetics underlying FSECs are associated with LGI family genes. In the present study, we cloned and characterized the feline LGI1-4 genes and examined their association with FSECs. Conventional PCR techniques were performed for cloning and mutational analysis. Characterization was predicted using bioinformatics software.

RESULTS

The cDNAs of feline LGI1-4 contained 1674-bp, 1650-bp, 1647-bp, and 1617-bp open reading frames, respectively, and encoded proteins comprising 557, 549, 548, and 538 amino acid residues, respectively. The feline LGI1-4 putative protein sequences showed high homology with Homo sapiens, Canis familiaris, Bos taurus, Sus scrofa, and Equus caballus (92%-100%). Mutational analysis in 8 FSECs and 8 controls for LGI family genes revealed 3 non-synonymous and 14 synonymous single nucleotide polymorphisms in the coding region. Only one non-synonymous single nucleotide polymorphism in LGI4 was found in 3 out of 8 FSECs. Using three separate computational tools, this mutation was not predicted to be disease causing. No co-segregation of the disease was found with any variant.

CONCLUSIONS

We cloned the cDNAs of the four feline LGI genes, analyzed the amino acid sequences, and revealed that epilepsy in FSEC is not a monogenic disorder associated with LGI genes.

Leucine-rich glioma inactivated 3: integrative analyses support its prognostic role in glioma

Background

Leucine-rich glioma inactivated 3 (LGI3) is a secreted protein member of LGI family. We previously reported that LGI3 was expressed in brain, adipose tissues and skin, where it played roles as a multifunctional cytokine. We postulated that LGI3 may be involved in cytokine network in cancers.

Aim

This study aimed to analyze differentially expressed genes in glioma tissues and glioma cohort data to investigate the prognostic role of LGI3 and its receptors.

Materials and methods

Expression microarray data from Gene Expression Omnibus and glioma cohort data were analyzed using bioinformatic tools for statistical analysis, protein–protein interactions, functional enrichment and pathway analyses and prognostic association analysis.

Results

We found that LGI3 and its receptors, ADAM22 and ADAM23, were significantly downregulated in glioma tissues. Eleven upregulated genes and two downregulated genes in glioma tissues were found to be the previously reported LGI3-regulated genes. Protein–protein interaction network analysis showed that 85% of the LGI3-regulated and glioma-altered genes formed a cluster of interaction network. Functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed the association of these genes with hypoxia responses, p53 and Akt signaling and various cancer-related pathways including glioma. Analysis of expression microarray data of glioma cohorts demonstrated that low expression levels of LGI3, ADAM22 and ADAM23 were significantly associated with poor prognosis of glioma.

Conclusion

These results propose that LGI3 and its receptors may play a prognostic role in glioma.

Motor cortex and hippocampus are the two main cortical targets in LGI1-antibody encephalitis

Encephalitis associated with antibodies against leucine-rich glioma-inactivated 1 (LGI1) protein is increasingly recognized as an auto-immune disorder associated with characteristic tonic-dystonic seizures. The cortical or subcortical origin of these motor events is not clear. Some patients also present with different epileptic seizures and with cognitive impairment. The frequency of these features and their timing during the natural history of this encephalitis have not been fully described. We therefore reviewed data from 34 patients harbouring antibodies against LGI1 protein (21-81 years, median age 64) referred to the French Reference Centre for Neurological Paraneoplastic Syndrome. Three types of evidence suggested tonic-dystonic seizures were of cortical origin: (i) a slow, unilateral, frontal electroencephalographic wave, of duration ∼580 ms and amplitude ∼71 µV, preceded the contralateral tonic-dystonic seizures in simultaneous electroencephalographic and myographic records from seven of seven patients tested; (ii) 18-Fluorodeoxyglucose imaging revealed a strong hypermetabolism in primary motor cortex, controlateral to the affected limb, during encephalitis for five patients tested, as compared with data from the same patients after remission or from 16 control subjects; and (iii) features of polymyographic records of tonic-dystonic seizure events pointed to a cortical origin. Myoclonic patterns with brief, rhythmic bursts were present in three of five patients tested and a premyoclonic potential was identified in the cortex of one patient. Initially during encephalitis, 11 of 34 patients exhibited tonic-dystonic seizures (32%). Distinct epileptic syndromes were evident in 13 patients (38%). They were typically simple, focal seizures from the temporal lobe, consisting of vegetative symptoms or fear. At later stages, 22 of 32 patients displayed tonic-dystonic seizures (68%) and 29 patients presented frequent seizures (91%) including status epilepticus. Cognitive impairment, either anterograde amnesia or confusion was evident in 30 of 34 patients (88%). Brain imaging was normal in patients with isolated tonic-dystonic seizures; in patients with limbic symptoms it revealed initially a hippocampal hyperintensity in 8 of 19 patients (42%) and 17 of 24 patients (70%) at later stages. Our data suggest that the major signs of LGI1-antibody encephalitis can be linked to involvement of motor cortex and hippocampus. They occur in parallel with striatum involvement. One of these cortical targets is involved, often unilaterally at disease onset. As the encephalitis progresses, in the absence of immunomodulatory treatment, the second cortical target is affected and effects become bilateral. Progression to the second cortical target occurs with a variable delay of days to several months.

Functional phylogenetic analysis of LGI proteins identifies an interaction motif crucial for myelination

The cellular interactions that drive the formation and maintenance of the insulating myelin sheath around axons are only partially understood. Leucine-rich glioma-inactivated (LGI) proteins play important roles in nervous system development and mutations in their genes have been associated with epilepsy and amyelination. Their function involves interactions with ADAM22 and ADAM23 cell surface receptors, possibly in apposing membranes, thus attenuating cellular interactions. LGI4-ADAM22 interactions are required for axonal sorting and myelination in the developing peripheral nervous system (PNS). Functional analysis revealed that, despite their high homology and affinity for ADAM22, LGI proteins are functionally distinct. To dissect the key residues in LGI proteins required for coordinating axonal sorting and myelination in the developing PNS, we adopted a phylogenetic and computational approach and demonstrate that the mechanism of action of LGI4 depends on a cluster of three amino acids on the outer surface of the LGI4 protein, thus providing a structural basis for the mechanistic differences in LGI protein function in nervous system development and evolution.

LGI1: from zebrafish to human epilepsy

Mutations in the LGI1 gene predispose to autosomal dominant lateral temporal lobe epilepsy, a rare hereditary form with incomplete penetrance and associated with acoustic auras. LGI1 is not a structural component of an ion channel like most epilepsy-related genes, but is a secreted protein. Mutant null mice exhibit early-onset seizures, and electrophysiological analysis shows abnormal synaptic transmission. LGI1 binds to ADAM23 on the presynaptic membrane and ADAM22 on the postsynaptic membrane, further implicating it in regulating the strength of synaptic transmission. Patients with limbic encephalitis show autoantibodies against LGI1 and develop seizures, supporting a role for LGI1 in synapse transmission in the post developmental brain. LGI1, however, also seems to be involved in aspects of neurite development and dendritic pruning, suggesting an additional role in corticogenesis. LGI1 is also involved in cell movement and suppression of dendritic outgrowth in in vitro systems, possibly involving actin cytoskeleton dynamics. Expression patterns in embryonic development correspond to areas of neuronal migration. Loss of LGI1 expression also impacts on myelination of the central and peripheral nervous systems. In zebrafish embryos, knockdown of lgi1a leads to a seizure-like behavior and abnormal brain development, providing a system to study its role in early embryogenesis. Despite being implicated in a role in both synapse transmission and neuronal development, how LGI1 predisposes to epilepsy is still largely unknown. It appears, however, that LGI1 may function differently in a cell context-specific manner, implying a complex involvement in brain development and function that remains to be defined.

LGI proteins in the nervous system

The development and function of the vertebrate nervous system depend on specific interactions between different cell types. Two examples of such interactions are synaptic transmission and myelination. LGI1-4 (leucine-rich glioma inactivated proteins) play important roles in these processes. They are secreted proteins consisting of an LRR (leucine-rich repeat) domain and a so-called epilepsy-associated or EPTP (epitempin) domain. Both domains are thought to function in protein–protein interactions. The first LGI gene to be identified, LGI1, was found at a chromosomal translocation breakpoint in a glioma cell line. It was subsequently found mutated in ADLTE (autosomal dominant lateral temporal (lobe) epilepsy) also referred to as ADPEAF (autosomal dominant partial epilepsy with auditory features). LGI1 protein appears to act at synapses and antibodies against LGI1 may cause the autoimmune disorder limbic encephalitis. A similar function in synaptic remodelling has been suggested for LGI2, which is mutated in canine Benign Familial Juvenile Epilepsy. LGI4 is required for proliferation of glia in the peripheral nervous system and binds to a neuronal receptor, ADAM22, to foster ensheathment and myelination of axons by Schwann cells. Thus, LGI proteins play crucial roles in nervous system development and function and their study is highly important, both to understand their biological functions and for their therapeutic potential. Here, we review our current knowledge about this important family of proteins, and the progress made towards understanding their functions.

Leucine-rich glioma inactivated 3 associates negatively with adiponectin

Leucine-rich glioma inactivated 3 (LGI3) is a secreted protein member of LGI/epitempin family. We previously reported that LGI3 was expressed in adipose tissues and suppressed adipogenesis through its receptor, ADAM23. We proposed that LGI3 may be a candidate adipokine with pro-inflammatory activity. To investigate the role of LGI3 in adipose tissues, we analyzed cytokine profile in LGI3 knockout mice. Protein array analysis showed that adiponectin was significantly increased in adipose tissues and plasma of LGI3 knockout mice. SiRNA-mediated knockdown of LGI3 increased adiponectin in 3T3-L1 preadipocytes. Treatment of differentiating 3T3-L1 cells with LGI3 protein decreased adiponectin in a dose-dependent manner. High fat diet (HFD)-fed mice showed expression of LGI3 in adipose tissue macrophages in addition to adipocytes that expressed LGI3 in both normal chow-fed and HFD-fed mice. The 60-kDa LGI3 was selectively increased in adipose tissues of HFD mice in which adiponectin was downregulated. Taken together, these results suggested that LGI3 may participate in adipose tissue homeostasis by negatively regulating adiponectin.

Leucine-rich glioma inactivated 3 regulates adipogenesis through ADAM23

Leucine-rich glioma inactivated 3 (LGI3) is a secreted protein and a member of LGI/epitempin family. We previously showed that LGI3 was highly expressed in brain and played regulatory roles in neuronal exocytosis and differentiation. Besides the nervous system, LGI3 was shown to be expressed in diverse tissues. In this study, we found that LGI3 and its receptor candidate ADAM23 were expressed in adipose tissues and 3T3-L1 cells. 3T3-L1 preadipocytes secreted a 60-kDa protein, a major secreted form of LGI3, which declined with adipocyte differentiation. LGI3 was also expressed in adipose tissue macrophages in the ob/ob mice and in macrophage cell line. The 60-kDa LGI3 protein was selectively increased in the ob/ob adipose tissues comparing with the lean mice. Pull-down experiments, coimmunoprecipitation and immunocytochemistry indicated that LGI3 associated with ADAM23 in adipose tissues and 3T3-L1 cells. Knockdown of LGI3 or ADAM23 by siRNA increased adipogenesis in 3T3-L1 cells. Treatment with LGI3 protein did not affect preadipocyte proliferation but attenuated adipogenesis and this effect was reversed by siRNA-mediated knockdown of ADAM23. Taken together, we propose that LGI3 may be a candidate adipokine that is perturbed in obesity and suppresses adipogenesis through its receptor, ADAM23.

Microarray data integration for genome-wide analysis of human tissue-selective gene expression

Background

Microarray gene expression data are accumulating in public databases. The expression profiles contain valuable information for understanding human gene expression patterns. However, the effective use of public microarray data requires integrating the expression profiles from heterogeneous sources.

Results

In this study, we have compiled a compendium of microarray expression profiles of various human tissue samples. The microarray raw data generated in different research laboratories have been obtained and combined into a single dataset after data normalization and transformation. To demonstrate the usefulness of the integrated microarray data for studying human gene expression patterns, we have analyzed the dataset to identify potential tissue-selective genes. A new method has been proposed for genome-wide identification of tissue-selective gene targets using both microarray intensity values and detection calls. The candidate genes for brain, liver and testis-selective expression have been examined, and the results suggest that our approach can select some interesting gene targets for further experimental studies.

Conclusion

A computational approach has been developed in this study for combining microarray expression profiles from heterogeneous sources. The integrated microarray data can be used to investigate tissue-selective expression patterns of human genes.

Positive association between benign familial infantile convulsions and LGI4

PURPOSE

LGI4 is located in 19q13.11, where the locus of benign familial infantile convulsions (BFIC) has been mapped. LGI4 belongs to a family of proteins with the epilepsy-associated repeat (EAR) domain and is associated with various epilepsies. We investigated whether LGI4 is a candidate gene for BFIC.

METHODS

Fifteen patients with BFIC were examined for mutations and/or polymorphisms of LGI4 by using a direct sequencing method.

RESULTS

Several frequent polymorphisms were identified. The genotype frequency distribution of c.1722G/A polymorphism was significantly different between patients with BFIC and control subjects (p<0.05). Logistic regression analysis showed that the G allele of c.1722G/A polymorphism had significant recessive effects on the increased relative risk for BFIC (p<0.05). There was no association between c.1722G/A polymorphism and benign familial neonatal convulsion, an epilepsy phenotype similar to BFIC but genetically distinguished from BFIC.

DISCUSSION

The positive genotypic association between BFIC and c.1722G/A polymorphism suggests that LGI4 might contribute to the susceptibility to BFIC.

Studies on the very large G protein-coupled receptor: from initial discovery to determining its role in sensorineural deafness in higher animals

The very large G protein-coupled receptor 1 (VLGRI), also known as MASS1 or GPR98, is most notable among the family of adhesion-GPCR for its size. Encoded by an 18.9 kb open reading frame, the approximately 700 kDa primary translation product is by far the largest GPCR and additionally, the largest cell surface protein known to date. The large ectodomain of the protein contains several repeated motifs, including some 35 calcium binding, Calx-beta repeats and seven copies of an epitempin repeat thought to be associated with the development of epilepsy. The extreme carboxy-terminus contains a consensus PDZ ligand sequence, suggesting interactions with other cytosolic or cytoskeletal proteins. At least two spontaneous and two targeted mutant mouse lines are currently known. The mutant mice present with sensitivity to audiogenic seizures but also have cochlear defects and significant, progressive hearing impairment. Although its ligand is currently unknown, VLGR1 is one of the few adhesion-GPCR family members in which mutations have been shown to be responsible for a human malady. Mutations in VLGRI in humans result in one form (2C) of Usher syndrome, the most common genetic cause of combined blindness and deafness.

LGI1-associated epilepsy through altered ADAM23-dependent neuronal morphology

Most epilepsy genes encode ion channels, but the LGI1 gene responsible for autosomal dominant partial epilepsy with auditory features produces a secreted protein. LGI1 is suggested to regulate PSD-95 via ADAM22. However, no unbiased screen of LGI1 action has been conducted. Here, we searched for brain genes supporting high affinity LGI-1 binding. ADAM23 was the only LGI1 interactor identified. The related proteins, ADAM22 and ADAM11, but not ADAM12, bind LGI1. Neither ADAM23 nor ADAM11, nor some forms of ADAM22, contain PDZ-interacting sequences, suggesting PSD-95-independent mechanisms in ADPEAF. Because ADAMs modulate integrins, we examined LGI1 effect on neurite outgrowth. LGI1 increases outgrowth from wild-type but not ADAM23-/- neurons. Furthermore, CA1 pyramidal neurons of ADAM23-/- hippocampi have reduced dendritic arborization. ADAM23-/- mice exhibit spontaneous seizures, while ADAM23+/- mice have decreased seizure thresholds. Thus, LGI1 binding to ADAM23 is necessary to correctly pattern neuronal morphology and altered anatomical patterning contributes to ADPEAF.

A de novo KCNQ2 mutation detected in non-familial benign neonatal convulsions

BACKGROUND

The underlying genetic abnormalities of rare familial idiopathic epilepsy have been identified, such as mutation in KCNQ2, a K(+) channel gene. Yet, few genetic abnormalities have been reported for commoner epilepsy, i.e., sporadic idiopathic epilepsy, which share a phenotype similar to those of familial epilepsy.

OBJECTIVE

To search for the genetic cause of seizures in a girl with the diagnosis of non-familial benign neonatal convulsions, and define the consequence of the genetic abnormality identified.

METHODS

Genetic abnormality was explored within candidate genes for benign familial neonatal and infantile convulsions, such as KCNQ2, 3, 5, KCNE2, SCN1A and SCN2A. The electrophysiological properties of the channels harboring the identified mutation were examined. Western blotting and immunostaining were employed to characterize the expression and intracellular localization of the mutant channel molecules.

RESULTS

A novel heterozygous mutation (c.910-2delTTC or TTT, Phe304del) of KCNQ2 was identified in the patient. The mutation was de novo verified by parentage analysis. The mutation was associated with impaired functions of KCNQ K(+) channel. The mutant channels were expressed on the cell surface.

CONCLUSION

The mutant Phe304del of KCNQ2 leads to null function of the KCNQ K(+) channel but the mutation does not alter proper channel sorting onto the cell membrane. Our findings indicate that the genes responsible for rare inherited forms of idiopathic epilepsy could be also involved in sporadic forms of idiopathic epilepsy and expand our notion of the involvement of molecular mechanisms in the more common forms of idiopathic epilepsy.

Leucine-rich glioma inactivated 3 associates with syntaxin 1

Leucine-rich glioma inactivated 3 (LGI3) is a member of LGI/epitempin (EPTP) family. The biological function of LGI3 and its association with disease are not known. We previously reported that mouse LGI3 was highly expressed in brain in a developmentally and transcriptionally regulated manner. In this study, we identified syntaxin 1, a SNARE component in exocytosis, as a candidate functional target of LGI3. Western blot analysis of mouse brain extract with LGI3 antibodies detected multiple protein forms (75-, 60-, 35- and 25-kDa). Proteomic analysis, pull-down and coimmunoprecipitation experiments identified syntaxin 1 as an LGI3-associated protein. LGI3 colocalized with syntaxin 1 in processes of cortical neurons with punctate synaptic pattern and was enriched in synaptosomal fraction. Coimmunoprecipitation showed that LGI3-syntaxin 1 complex did not contain other SNARE components, SNAP25 and VAMP2. Recombinant LGI3 attenuated Ca(2+)-evoked glutamate release from digitonin-permeabilized synaptosomes and transfection of PC12 cells with LGI3 decreased K(+)-induced secretion of human growth hormone. Thus, LGI3 may play a regulatory role in neuronal exocytosis via its interaction with syntaxin 1.

Genetics and epilepsy

The term “epilepsy” describes a heterogeneous group of disorders, most of them caused by interactions between several or even many genes and environmental factors. Much rarer are the genetic epilepsies that are due to single-gene mutations or defined structural chromosomal aberrations, such as microdeletions. The discovery of several of the genes underlying these rare genetic epilepsies has already considerably contributed to our understanding of the basic mechanisms epileptogenesis. The progress made in the last 15 years in the genetics of epilepsy is providing new possibilities for diagnosis and therapy. Here, different genetic epilepsies are reviewed as examples, to demonstrate the various pathways that can lead from genes to seizures.

Early vertebrate chromosome duplications and the evolution of the neuropeptide Y receptor gene regions

Background

One of the many gene families that expanded in early vertebrate evolution is the neuropeptide (NPY) receptor family of G-protein coupled receptors. Earlier work by our lab suggested that several of the NPY receptor genes found in extant vertebrates resulted from two genome duplications before the origin of jawed vertebrates (gnathostomes) and one additional genome duplication in the actinopterygian lineage, based on their location on chromosomes sharing several gene families. In this study we have investigated, in five vertebrate genomes, 45 gene families with members close to the NPY receptor genes in the compact genomes of the teleost fishes Tetraodon nigroviridis and Takifugu rubripes. These correspond to Homo sapiens chromosomes 4, 5, 8 and 10.

Results

Chromosome regions with conserved synteny were identified and confirmed by phylogenetic analyses in H. sapiens, M. musculus, D. rerio, T. rubripes and T. nigroviridis. 26 gene families, including the NPY receptor genes, (plus 3 described recently by other labs) showed a tree topology consistent with duplications in early vertebrate evolution and in the actinopterygian lineage, thereby supporting expansion through block duplications. Eight gene families had complications that precluded analysis (such as short sequence length or variable number of repeated domains) and another eight families did not support block duplications (because the paralogs in these families seem to have originated in another time window than the proposed genome duplication events). RT-PCR carried out with several tissues in T. rubripes revealed that all five NPY receptors were expressed in the brain and subtypes Y2, Y4 and Y8 were also expressed in peripheral organs.

Conclusion

We conclude that the phylogenetic analyses and chromosomal locations of these gene families support duplications of large blocks of genes or even entire chromosomes. Thus, these results are consistent with two early vertebrate tetraploidizations forming a paralogon comprising human chromosomes 4, 5, 8 and 10 and one teleost tetraploidization. The combination of positional and phylogenetic data further strengthens the identification of orthologs and paralogs in the NPY receptor family.

Immunohistochemical and biochemical analyses of LGI3 in monkey brain: LGI3 accumulates in aged monkey brains

Leucine-rich glioma inactivated (LGI) 3 encodes a leucine-rich repeat protein. The precise function of LGI3, however, remains unknown. We have previously shown that amyloid-beta peptide (Abeta) upregulates LGI3 and that Abeta and LGI3 colocalize on plasma membranes of cultured rat astrocytes. In the present study, we performed immunohistochemical and biochemical analyses of LGI3 using various aged monkey brains. Immunohistochemistry showed that LGI3 was present in almost all neural cells and mainly localized at plasma membranes and nuclei. In aged monkey brains, we found that LGI3 accumulated on or near the plasma membranes of neurons, and colocalized with endocytosis-associated proteins and lipid raft markers. Double immunohistochemistry also showed that LGI3 colocalized with Abeta in astrocytes of aged brains. Moreover, Western blot analyses revealed that LGI3 may be cleaved in brain. Additionally, in aged monkeys LGI3 accumulated in microsomal and nuclear brain fractions.

Absence of mutations in the LGI1 receptor ADAM22 gene in autosomal dominant lateral temporal epilepsy

Mutations in the LGI1 (leucine-rich, glioma inactivated 1) gene are found in less than a half of the families with autosomal dominant lateral temporal epilepsy (ADLTE), suggesting that ADLTE is a genetically heterogeneous disorder. Recently, it was shown that LGI1 is released by neurons and becomes part of a protein complex at the neuronal postsynaptic density where it is implicated in the regulation of glutamate-AMPA neurotransmission. Within this complex, LGI1 binds selectively to a neuronal specific membrane protein, ADAM22 (a disintegrin and metalloprotease). Since ADAM22 serves as a neuronal receptor for LGI1, the ADAM22 gene was considered a good candidate gene for ADLTE. We have therefore sequenced all coding exons and exon-intron flanking sites in the ADAM22 gene in the probands of 18 ADLTE families negative for LGI1 mutations. Although, we identified several synonymous and non-synonymous polymorphisms, we failed to identify disease-causing mutations, indicating that ADAM22 gene is probably not a major gene for this epilepsy syndrome.

Defining the expression pattern of the LGI1 gene in BAC transgenic mice

The LGI1 gene has been implicated in the development of epilepsy and the invasion phenotype of glial cells. Controversy over the specific tissue expression pattern of this gene has stemmed from conflicting reports generated using immunohistochemistry and the polymerase chain reaction. LGI1 is one of a four-member family of secreted proteins with high homology and here we demonstrate, using GFP-tagged constructs from the four LGI1family members, that commonly used antibodies against LGI1 cross-react with different family members. With the uncertainty surrounding the use of commercially available antibodies to truly establish the expression pattern of LGI1, we generated transgenic mice carrying the LGI1-containing BAC, RP23-127G7, which had been modified to express the GFP reporter gene under the control of the endogenous regulatory elements required for LGI1 expression. Three founder mice were generated, and immunohistochemistry was used to determine the tissue-specific pattern of expression. In the brain, distinct regions of glial and neuronal cell expression were identified, as well as the choriod plexus, which is largely pia-derived. In addition, strong expression levels were identified in glandular regions of the prostate, individual tubules in the kidney, sympathetic ganglia in the kidney, sebaceous glands in the skin, the islets of Langerhans, the endometrium, and the ovary and testes. All other major organs analyzed were negative. The pattern of reporter gene expression was identical in three individual founder mice, arguing against a position effect altering expression profile due to the integration site of the BAC.

Abeta upregulates and colocalizes with LGI3 in cultured rat astrocytes

1. The leucine-rich glioma inactivated (LGI) family of genes encodes a leucine-rich repeat (LRR) protein, proteins that are thought to be specifically involved in protein-protein and protein-matrix interactions. Since amyloid beta peptide (Abeta) has been previously shown to induce the expression of another LRR-encoding gene in neural cells, we assessed how Abeta affects LGI gene expression in rat primary cerebral cortical cultures and astrocyte cultures. Both RT-PCR and Western Blotting analyses revealed that Abeta robustly induced the expression of LGI3 in rat astrocyte cultures.2. Western Blotting analyses also showed that both glial fibrillary acidic protein (GFAP) and apolipoprotein E (ApoE) significantly increased coincidentally with the Abeta-induced upregulation of LGI3. Immunocytochemistry showed that LGI3 colocalized with Abeta at plasma membranes and also with internalized Abeta in astrocytes. These findings suggest that activated LGI3 may be involved in the astroglial response against Abeta.

Implicating A-current in a hereditary partial epilepsy

The Epilepsy-Linked Lgi1 Protein Assembles into Presynaptic Kv1 Channels and Inhibits Inactivation by Kvβ1

Schulte U, Thumfart JO, Klocker N, Sailer CA, Bildl W, Biniossek M, Dehn D, Deller T, Eble S, Abbass K, Wangler T, Knaus HG, Fakler B

Neuron 2006;49:697–706

The voltage-gated potassium (Kv) channel subunit Kv1.1 is a major constituent of presynaptic A-type channels that modulate synaptic transmission in CNS neurons. Here, we show that Kv1.1-containing channels are complexed with Lgi1, the functionally unassigned product of the leucine-rich glioma inactivated gene 1 (LGI1), which is causative for an autosomal dominant form of lateral temporal lobe epilepsy (ADLTE). In the hippocampal formation, both Kv1.1 and Lgi1 are coassembled with Kv1.4 and Kv β1 in axonal terminals. In A-type channels composed of these subunits, Lgi1 selectively prevents N-type inactivation mediated by the Kv β1 subunit. In contrast, defective Lgi1 molecules identified in ADLTE patients fail to exert this effect resulting in channels with rapid inactivation kinetics. The results establish Lgi1 as a novel subunit of Kv1.1-associated protein complexes and suggest that changes in inactivation gating of presynaptic A-type channels may promote epileptic activity.

The epilepsy gene LGI1 encodes a secreted glycoprotein that binds to the cell surface

Autosomal dominant lateral temporal epilepsy (ADTLE) is a partial epilepsy caused by mutations in LGI1, a multidomain protein of unknown function. To begin to understand the biological function of LGI1, we have determined its pattern of glycosylation, subcellular expression and capacity for secretion. LGI1 is expressed as two different isoforms in the brain, and we show that the long isoform is a secreted protein, whereas the short isoform is retained in an intracellular pool. ADLTE-related mutants of the long form are defective for secretion and are retained in the endoplasmic reticulum and Golgi complex. Finally, we show that normal secreted LGI1 specifically binds to the cell surface of differentiated PC12 cells. We propose that LGI1 is a secreted factor important for neuronal development and that ADTLE is a disease that results from the loss of regulation in the protein available either extracellular or intracellularly.

Localization of nyctalopin in the mammalian retina

Complete X-linked congenital stationary night blindness (CSNB1) is a hereditary visual disease characterized by abnormalities in both the dark- and light-adapted electroretinogram, consistent with a defect in synaptic transmission between photoreceptors and ON-bipolar cells. The gene responsible for CSNB1, NYX, encodes a novel, leucine-rich repeat protein, nyctalopin. Consistent with its predicted glycosylphosphatidylinositol linkage, we show that recombinant nyctalopin is targeted to the extracellular cell surface in transfected HEK293 cells. Within the retina, strong nyctalopin immunoreactivity is present in the outer plexiform layer, the site of the photoreceptor to bipolar cell synapses. Double labelling of nyctalopin and known synaptic proteins in the outer plexiform layer indicate that nyctalopin is associated with the ribbon synapses of both rod and cone terminals. In the inner plexiform layer, nyctalopin immunoreactivity is associated with rod bipolar cell terminals. Our findings support a role for nyctalopin in synaptic transmission and/or synapse formation at ribbon synapses in the retina.

AMIGO and friends: An emerging family of brain-enriched, neuronal growth modulating, type I transmembrane proteins with leucine-rich repeats (LRR) and cell adhesion molecule motifs

Leucine-rich repeats (LRR) are protein-protein interaction domains (20-29 amino acid residues in length) found in proteins with diverse structure and functions. We note here an emerging group of central nervous system-enriched, type I surface proteins with an ectodomain containing LRR repeats and motifs found in cell adhesion molecules. Members of this group include the Amphoterin-induced gene and ORF-1 (AMIGO-1), LRR and Ig domain containing Nogo Receptor interacting protein I (LINGO-1) and the netrin-G1 ligand NGL-1. The above proteins carry, in addition to the LRR repeats, an immunoglobin (Ig)-like segment in their ectodomain. Two other related families of molecules, the NLRRs and the FLRTs, have in addition, a fibronectin type III repeat. The LRR domain distinguishes these molecules from the more extensively studied Ig-like family of cell adhesion molecules, and the transmembrane domain differentiate them from the family of secreted extracellular proteoglycans with LRRs. Functionally, many members of this group of proteins could modulate neurite outgrowth of neurons, at least in vitro. LINGO-1, initially discovered as a component of the Nogo-66 receptor complex which inhibits neurite growth, also regulates oligodendrocyte differentiation and myelination. Current knowledge and recent findings pertaining to the functions of this interesting group of proteins in the nervous system are discussed.

The LGI1/Epitempin gene encodes two protein isoforms differentially expressed in human brain

The leucine-rich, glioma inactivated 1 (LGI1)/Epitempin gene has been linked to two phenotypes as different as gliomagenesis and autosomal dominant lateral temporal epilepsy. Its function and the biochemical features of the encoded protein are unknown. We characterized the LGI1/Epitempin protein product by western blot analysis of mouse and human brain tissues. Two proteins of about 60 and 65 kDa were detected by an anti-LGI1 antibody within the expected molecular mass range. The two proteins appeared to reside in different subcellular compartments, as they were fractionated by differential centrifugation. The specificity of both polypeptides was validated by cell transfection assay and mass spectrometry analysis. Immunoblot analysis of protein distribution in various zones of the human brain revealed variable amounts of both proteins. Notably, these proteins were more abundant in the temporal neocortex than in the hippocampus, the difference in abundance of the 65-kDa product being particularly pronounced. These results suggest that the two protein isoforms encoded by LGI1/Epitempin are differentially expressed in the human brain, and that higher expression levels of these proteins in the lateral temporal cortex may underlie the susceptibility of this brain region to the epileptogenic effects of LGI1/Epitempin mutations.

Axonemal protofilament ribbons, DM10 domains, and the link to juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy (JME) is a common neurological disorder that results in short uncontrolled muscle contractions and sometimes more severe seizures. Genetic studies have suggested that JME may be caused by mutations in EFHC1. The Efhc1 protein consists of three DM10 domains and a C-terminal region containing a potential Ca2+ -binding motif. In Chlamydomonas, a protein (Rib72) of almost identical domain structure is a component of the protofilament ribbons within the doublet microtubules of the flagellar axoneme. Here I discuss recent work that supports assignment of human Efhc1 as a ciliary component and the resulting implications for the mechanism of disease causation.

Mouse LGI3 gene: expression in brain and promoter analysis

Leucine-rich glioma inactivated 3 (LGI3) is a member of LGI/epitempin family of which the first member, LGI1/epitempin, was shown to be mutated in glioma and autosomal dominant lateral temporal epilepsy. Similar to LGI1, LGI3 is expressed predominantly in brain and its function is unknown. In this study, we examined the expression of mouse LGI3 (mLGI3) in adult and developing brain and analyzed the 5'-upstream transcriptional regulatory regions of mLGI3 gene. In situ hybridization showed that mLGI3 was expressed in widespread areas with selective regional variation in adult brain. In developing brain, mLGI3 mRNA was expressed at low level during embryo stages and markedly increased in broad areas after birth. Analysis of the 5'- and 3'-ends of mLGI3 mRNA identified a single transcription start site and two alternative 3'-ends. Luciferase reporter analysis using Neuro-2a cells and electrophoretic mobility shift assays identified a neuronal restrictive silencer element (NRSE; -2573 approximately -2553) and a phorbol ester-sensitive AP-2 element with repressor activity (-44 approximately -33) among multiple positive and negative regulatory regions. Since NRSE and AP-2 are implicated in neuron-specific gene expression and developmental regulation of many genes in brain, respectively, these results suggested that NRSE and AP-2 might play important roles in regulation of mLGI3 expression in brain.

Determination of genomic breakpoints in an epileptic patient using genotyping array

Recent advances in DNA microarray technology have enabled the identification of small alterations throughout the genome. We used standard karyotype analysis, followed by DNA microarray analysis and PCR to precisely map the chromosomal 4p deletion and determine the deletion breakpoints in the genome of an epileptic patient. The karyotype of the patient was 46,XY,del(4)(p15.2p15.3) as determined by G-banding analysis. We used a high-density oligonucleotide genotyping array to estimate the size of the deletion (4.5 Mb) and to locate the breakpoints within a 9-kb region on one side of the deletion and a 100-kb region on the other side. We amplified by PCR and sequenced the genomic region encompassing the breakpoints, and mapped the deletion to regions extending from 21648457 to 26164287 and from 26164505 to 26167493, respectively (chromosome 4 of NCBI Homo sapiens Genome Build 35.1). The deletion involves 18 genes, one of which (CCKAR) is partially deleted.

The claw paw mutation reveals a role for Lgi4 in peripheral nerve development

Peripheral nerve development results from multiple cellular interactions between axons, Schwann cells and the surrounding mesenchymal tissue. The delayed axonal sorting and hypomyelination throughout the peripheral nervous system of claw paw (clp) mutant mice suggest that the clp gene product is critical for these interactions. Here we identify the clp mutation as a 225-bp insertion in the Lgi4 gene. Lgi4 encodes a secreted and glycosylated leucine-rich repeat protein and is expressed in Schwann cells. The clp mutation affects Lgi4 mRNA splicing, resulting in a mutant protein that is retained in the cell. Additionally, siRNA-mediated downregulation of Lgi4 in wild-type neuron-Schwann cell cocultures inhibits myelination, whereas exogenous Lgi4 restores myelination in clp/clp cultures. Thus, the abnormalities observed in clp mice are attributable to the loss of Lgi4 function, and they identify Lgi4 as a new component of Schwann cell signaling pathway(s) that controls axon segregation and myelin formation.

Differential expression of the LGI and SLIT families of genes in human cancer cells

The LGI and SLIT genes have a distinctive leucine-rich repeat motif in the N-terminal end of the protein which is indicative of either receptor function or an interaction with the extracellular matrix. Members of the LGI and SLIT family of genes have been implicated in specific cancers and have been suggested to have a restricted pattern of expression in normal cells. To investigate the extent and distribution of the expression of these genes in cancer cells we have analyzed their expression levels in a range of tumor cell types. Different tumor types appear to hold a preference for the specific members of the families which are expressed. Differential expression between cell lines, from the same tumor type, implies a role for inactivation and reactivation of these genes during tumorigenesis. The detailed characterization of the expression pattern in these tumor cells offers the opportunity to perform a functional analysis of these individual genes.

A new EF-hand containing gene EFHC2 on Xp11.4: Tentative evidence for association with juvenile myoclonic epilepsy

Genetic factors play a major role in the etiology of idiopathic generalized epilepsies (IGE). An oligogenic or polygenic predisposition is suspected in the majority of families with common IGE syndromes. It has been hypothesized that some IGE genes might increase the general level of neuronal excitability while others specify the age of onset and the seizure type. The EFHC1 gene on 6p12-p11 was previously described as the first susceptibility gene for juvenile myoclonic epilepsy (JME). EFHC1 codes for a protein of unknown function that is characterized by Ca2+-binding EF-hand motifs and DM10 domains. We have now cloned the brain-expressed paralog EFHC2 (Xp11.3) and carried out an association study of six single nucleotide polymorphisms (SNPs) in a large sample of 654 German IGE patients and 662 population controls. A tentative association was found between the amino acid exchange S430Y in exon 9 of EFHC2 and 97 male JME patients (chi2=4.705, d.f.=1, P=0.030; OR=2.17; 95-CI: 1.06-4.43). The allelic association was even stronger for the 81 males with "classical" JME (JME without absence seizures) (chi2=6.06, d.f.=1, P=0.014; OR=2.46; 95-CI: 1.18-5.13). An association with the gonosomal gene EFHC2 would be in accordance with the observed preponderance of maternal inheritance in JME maternal inheritance of JME. Independent replication studies are needed to further analyse the tentative association described here.

Using Gene-History and Expression Analyses to Assess the Involvement of LGI Genes in Human Disorders

Mutations in the leucine-rich, glioma-inactivated 1 gene, LGI1, cause autosomal-dominant lateral temporal lobe epilepsy via unknown mechanisms. LGI1 belongs to a subfamily of leucine-rich repeat genes comprising four members (LGI1-LGI4) in mammals. In this study, both comparative developmental as well as molecular evolutionary methods were applied to investigate the evolution of the LGI gene family and, subsequently, of the functional importance of its different gene members. Our phylogenetic studies suggest that LGI genes evolved early in the vertebrate lineage. Genetic and expression analyses of all five zebrafish lgi genes revealed duplications of lgi1 and lgi2, each resulting in two paralogous gene copies with mostly nonoverlapping expression patterns. Furthermore, all vertebrate LGI1 orthologs experience high levels of purifying selection that argue for an essential role of this gene in neural development or function. The approach of combining expression and selection data used here exemplarily demonstrates that in poorly characterized gene families a framework of evolutionary and expression analyses can identify those genes that are functionally most important and are therefore prime candidates for human disorders.

LGI1: a gene involved in epileptogenesis and glioma progression?

The leucine-rich, glioma inactivated gene 1 (LGI1) gene on human chromosome 10q24 was first identified as a candidate tumor suppressor gene for glioma. Surprisingly, mutations in LGI1 were also shown to cause an idiopathic epilepsy syndrome, autosomal dominant lateral temporal lobe epilepsy (ADLTE). LGI1 is one of the only two currently known non-ion channel genes whose mutations cause idiopathic epilepsy in humans. In this review we summarize the current data on structure and function of the LGI1 protein and discuss clinical aspects of ADLTE and their correlation with LGI1. We also propose that the evidence supporting the tumor suppressor role of LGI1 in malignant gliomas is weak and that further work is necessary to establish LGI1 role in glial cells.

1274 full-open reading frames of transcripts expressed in the developing mouse nervous system

As part of the trans-National Institutes of Health (NIH) Mouse Brain Molecular Anatomy Project (BMAP), and in close coordination with the NIH Mammalian Gene Collection Program (MGC), we initiated a large-scale project to clone, identify, and sequence the complete open reading frame (ORF) of transcripts expressed in the developing mouse nervous system. Here we report the analysis of the ORF sequence of 1274 cDNAs, obtained from 47 full-length-enriched cDNA libraries, constructed by using a novel approach, herein described. cDNA libraries were derived from size-fractionated cytoplasmic mRNA isolated from brain and eye tissues obtained at several embryonic stages and postnatal days. Altogether, including the full-ORF MGC sequences derived from these libraries by the MGC sequencing team, NIH_BMAP full-ORF sequences correspond to approximately 20% of all transcripts currently represented in mouse MGC. We show that NIH_BMAP clones comprise 68% of mouse MGC cDNAs > or =5 kb, and 54% of those > or =4 kb, as of March 15, 2004. Importantly, we identified transcripts, among the 1274 full-ORF sequences, that are exclusively or predominantly expressed in brain and eye tissues, many of which encode yet uncharacterized proteins.

LGI1 mutations in autosomal dominant partial epilepsy with auditory features

OBJECTIVE

S: Mutations in LGI1 cause autosomal dominant partial epilepsy with auditory features (ADPEAF), a form of familial temporal lobe epilepsy with auditory ictal manifestations. The authors aimed to determine what proportion of ADPEAF families carries a mutation, to estimate the penetrance of identified mutations, and to identify clinical features that distinguish families with and without mutations.

METHODS

The authors sequenced LGI1 in 10 newly described ADPEAF families and analyzed clinical features in these families and others with mutations reported previously.

RESULTS

Three of the families had missense mutations in LGI1 (C42R, I298T, and A110D). Penetrance was 54% in eight families with LGI1 mutations the authors have identified so far (five reported previously and three reported here). Excluding the original linkage family, the authors have found mutations in 50% (7/14) of tested families. Families with and without mutations had similar clinical features, but those with mutations contained significantly more subjects with auditory symptoms and significantly fewer with autonomic symptoms. In families with mutations, the most common auditory symptom type was simple, unformed sounds (e.g., buzzing and ringing). In two of the newly identified families with mutations, some subjects with mutations had idiopathic generalized epilepsies.

CONCLUSIONS

LGI1 mutations are a common cause of autosomal dominant partial epilepsy with auditory features. Current data do not reveal a clinical feature that clearly predicts which families with autosomal dominant partial epilepsy with auditory features have a mutation. Some families with LGI1 mutations contain individuals with idiopathic generalized epilepsies. This could result from either an effect of LGI1 on risk for generalized epilepsy or an effect of co-occurring idiopathic generalized epilepsy-specific genes in these families.

Genes and mutations in human idiopathic epilepsy

Thirteen genes have already been identified in human idiopathic epilepsies since 1995, but they account only for a minority of all epilepsy cases. Most of these genes are associated with rare monogenic epilepsy syndromes, but some of them contribute to the common epilepsy subtypes. The questions remains to be answered how many more epilepsy genes exist in brain. Idiopathic epilepsies are common neurological disorders, and it can therefore be expected that the total number of genes associated with an increased seizure susceptibility is much higher than 13. Most of the known genes code for either voltage-gated or ligand gated ion channels, but recently two epilepsy genes have been found which do not fit into the concept of epilepsies as channelopathies. It can therefore be suspected that more than one pathogenetic concept exists in epileptogenesis.