LGI1 is mutated in familial temporal lobe epilepsy characterized by aphasic seizures

Faciobrachial dystonic seizures precede Lgi1 antibody limbic encephalitis

OBJECTIVE

To describe a distinctive seizure semiology that closely associates with voltage-gated potassium channel (VGKC)-complex/Lgi1 antibodies and commonly precedes the onset of limbic encephalitis (LE).

METHODS

Twenty-nine patients were identified by the authors (n = 15) or referring clinicians (n = 14). The temporal progression of clinical features and serum sodium, brain magnetic resonance imaging (MRI), positron emission tomography/single photon emission computed tomography, and VGKC-complex antibodies was studied.

RESULTS

Videos and still images showed a distinctive adult-onset, frequent, brief dystonic seizure semiology that predominantly affected the arm and ipsilateral face. We have termed these faciobrachial dystonic seizures (FBDS). All patients tested during their illness had antibodies to VGKC complexes; the specific antigenic target was Lgi1 in 89%. Whereas 3 patients never developed LE, 20 of the remaining 26 (77%) experienced FBDS prior to the development of the amnesia and confusion that characterize LE. During the prodrome of FBDS alone, patients had normal sodium and brain MRIs, but electroencephalography demonstrated ictal epileptiform activity in 7 patients (24%). Following development of LE, the patients often developed other seizure semiologies, including typical mesial temporal lobe seizures. At this stage, investigations commonly showed hyponatremia and MRI hippocampal high T2 signal; functional brain imaging showed evidence of basal ganglia involvement in 5/8. Antiepileptic drugs (AEDs) were generally ineffective and in 41% were associated with cutaneous reactions that were often severe. By contrast, immunotherapies produced a clear, and often dramatic, reduction in FBDS frequency.

INTERPRETATION

Recognition of FBDS should prompt testing for VGKC-complex/Lgi1 antibodies. AEDs often produce adverse effects; treatment with immunotherapies may prevent the development of LE with its potential for cerebral atrophy and cognitive impairment.

Similarity of molecular phenotype between known epilepsy gene LGI1 and disease candidate gene LGI2

Background

The LGI2 (leucine-rich, glioma inactivated 2) gene, a prime candidate for partial epilepsy with pericentral spikes, belongs to a family encoding secreted, beta-propeller domain proteins with EPTP/EAR epilepsy-associated repeats. In another family member, LGI1 (leucine-rich, glioma inactivated 1) mutations are responsible for autosomal dominant lateral temporal epilepsy (ADLTE). Because a few LGI1 disease mutations described in the literature cause secretion failure, we experimentally analyzed the secretion efficiency and subcellular localization of several LGI1 and LGI2 mutant proteins corresponding to observed non-synonymous single nucleotide polymorphisms (nsSNPs) affecting the signal peptide, the leucine-rich repeats and the EAR propeller.

Results

Mapping of disease-causing mutations in the EAR domain region onto a 3D-structure model shows that many of these mutations co-localize at an evolutionary conserved surface region of the propeller. We find that wild-type LGI2 is secreted to the extracellular medium in glycosylated form similarly to LGI1, whereas several mutant proteins tested in this study are secretion-deficient and accumulate in the endoplasmic reticulum. Interestingly, mutations at structurally homologous positions in the EAR domain have the same effect on secretion in LGI1 and LGI2.

Conclusions

This similarity of experimental mislocalization phenotypes for mutations at homologous positions of LGI2 and the established epilepsy gene LGI1 suggests that both genes share a potentially common molecular pathogenesis mechanism that might be the reason for genotypically distinct but phenotypically related forms of epilepsy.

Investigation of LGI1 as the antigen in limbic encephalitis previously attributed to potassium channels: a case series

BACKGROUND

Voltage-gated potassium channels are thought to be the target of antibodies associated with limbic encephalitis. However, antibody testing using cells expressing voltage-gated potassium channels is negative; hence, we aimed to identify the real autoantigen associated with limbic encephalitis.

METHODS

We analysed sera and CSF of 57 patients with limbic encephalitis and antibodies attributed to voltage-gated potassium channels and 148 control individuals who had other disorders with or without antibodies against voltage-gated potassium channels. Immunohistochemistry, immunoprecipitation, and mass spectrometry were used to characterise the antigen. An assay with HEK293 cells transfected with leucine-rich, glioma-inactivated 1 (LGI1) and disintegrin and metalloproteinase domain-containing protein 22 (ADAM22) or ADAM23 was used as a serological test. The identity of the autoantigen was confirmed by immunoabsorption studies and immunostaining of Lgi1-null mice.

FINDINGS

Immunoprecipitation and mass spectrometry analyses showed that antibodies from patients with limbic encephalitis previously attributed to voltage-gated potassium channels recognise LGI1, a neuronal secreted protein that interacts with presynaptic ADAM23 and postsynaptic ADAM22. Immunostaining of HEK293 cells transfected with LGI1 showed that sera or CSF from patients, but not those from control individuals, recognised LGI1. Co-transfection of LGI1 with its receptors, ADAM22 or ADAM23, changed the pattern of reactivity and improved detection. LGI1 was confirmed as the autoantigen by specific abrogation of reactivity of sera and CSF from patients after immunoabsorption with LGI1-expressing cells and by comparative immunostaining of wild-type and Lgi1-null mice, which showed selective lack of reactivity in brains of Lgi1-null mice. One patient with limbic encephalitis and antibodies against LGI1 also had antibodies against CASPR2, an autoantigen we identified in some patients with encephalitis and seizures, Morvan's syndrome, and neuromyotonia.

INTERPRETATION

LGI1 is the autoantigen associated with limbic encephalitis previously attributed to voltage-gated potassium channels. The term limbic encephalitis associated with antibodies against voltage-gated potassium channels should be changed to limbic encephalitis associated with LGI1 antibodies, and this disorder should be classed as an autoimmune synaptic encephalopathy.

FUNDING

National Institutes of Health, National Cancer Institute, and Euroimmun.

Disruption of LGI1-linked synaptic complex causes abnormal synaptic transmission and epilepsy

Epilepsy is a devastating and poorly understood disease. Mutations in a secreted neuronal protein, leucine-rich glioma inactivated 1 (LGI1), were reported in patients with an inherited form of human epilepsy, autosomal dominant partial epilepsy with auditory features (ADPEAF). Here, we report an essential role of LGI1 as an antiepileptogenic ligand. We find that loss of LGI1 in mice (LGI1(-/-)) causes lethal epilepsy, which is specifically rescued by the neuronal expression of LGI1 transgene, but not LGI3. Moreover, heterozygous mice for the LGI1 mutation (LGI1(+/-)) show lowered seizure thresholds. Extracellularly secreted LGI1 links two epilepsy-related receptors, ADAM22 and ADAM23, in the brain and organizes a transsynaptic protein complex that includes presynaptic potassium channels and postsynaptic AMPA receptor scaffolds. A lack of LGI1 disrupts this synaptic protein connection and selectively reduces AMPA receptor-mediated synaptic transmission in the hippocampus. Thus, LGI1 may serve as a major determinant of brain excitation, and the LGI1 gene-targeted mouse provides a good model for human epilepsy.

Reexpression of LGI1 in glioma cells results in dysregulation of genes implicated in the canonical axon guidance pathway

The LGI1 gene suppresses invasion in glioma cells and predisposes to epilepsy. In a gene expression array comparison between parental cells and T98G cell clones forced to express LGI1, we demonstrate that the canonical axon guidance pathway is the most significantly affected. In particular, aspects of axon guidance that involve reorganization of the actin cytoskeleton, which is also involved in cell movement and invasion, were affected. Analysis of actin fiber organization using fluorescence microscopy demonstrated that different T98G cell clones expressing the exogenous LGI1 gene show high levels of stress fibers compared with controls. Since stress fiber formation is associated with loss of cell mobility, we used scratch wound assays to demonstrate that LGI1-expressing clones show a significant reduction in cell mobility. LGI1 reexpression also resulted in loss of the PDGFRA and EGFR proteins, suggesting a rapid turnover of these receptors despite increased mRNA levels for PDGFRA. LGI1 suppression of invasion is associated with loss of ERK/MAPK1 activation. LGI1 is a secreted protein, and when the culture supernatant from cells expressing FLAG- and GFP-tagged proteins were applied to parental T98G cells, ERK/MAPK1 phosphorylation and cell mobility was suppressed, demonstrating that the LGI1 protein acts as a suppressive agent for cell movement in this assay. These observations support a previous suggestion that LGI1 can reduce cellular invasion in in vitro assays and, as a secreted agent, may be developed as a means of treating metastatic cancer. In addition, this observation provides a mechanistic link for LGI1's common role in metastasis and epilepsy development.

Genetic testing in the epilepsies--report of the ILAE Genetics Commission

In this report, the International League Against Epilepsy (ILAE) Genetics Commission discusses essential issues to be considered with regard to clinical genetic testing in the epilepsies. Genetic research on the epilepsies has led to the identification of more than 20 genes with a major effect on susceptibility to idiopathic epilepsies. The most important potential clinical application of these discoveries is genetic testing: the use of genetic information, either to clarify the diagnosis in people already known or suspected to have epilepsy (diagnostic testing), or to predict onset of epilepsy in people at risk because of a family history (predictive testing). Although genetic testing has many potential benefits, it also has potential harms, and assessment of these potential benefits and harms in particular situations is complex. Moreover, many treating clinicians are unfamiliar with the types of tests available, how to access them, how to decide whether they should be offered, and what measures should be used to maximize benefit and minimize harm to their patients. Because the field is moving rapidly, with new information emerging practically every day, we present a framework for considering the clinical utility of genetic testing that can be applied to many different syndromes and clinical contexts. Given the current state of knowledge, genetic testing has high clinical utility in few clinical contexts, but in some of these it carries implications for daily clinical practice.

LGI1 mutations in autosomal dominant and sporadic lateral temporal epilepsy

Autosomal dominant lateral temporal epilepsy (ADLTE) or autosomal dominant partial epilepsy with auditory features (ADPEAF) is an inherited epileptic syndrome with onset in childhood/adolescence and benign evolution. The hallmark of the syndrome consists of typical auditory auras or ictal aphasia in most affected family members. ADTLE/ADPEAF is associated in about half of the families with mutations of the leucine-rich, glioma-inactivated 1 (LGI1) gene. In addition, de novo LGI1 mutations are found in about 2% of sporadic cases with idiopathic partial epilepsy with auditory features, who are clinically similar to the majority of patients with ADLTE/ADPEAF but have no family history. Twenty-five LGI1 mutations have been described in familial and sporadic lateral temporal epilepsy patients. The mutations are distributed throughout the gene and are mostly missense mutations occurring in both the N-terminal leucine rich repeat (LRR) and C-terminal EPTP (beta propeller) protein domains. We show a tridimensional model of the LRR protein region that allows missense mutations of this region to be divided into two distinct groups: structural and functional mutations. Frameshift, nonsense and splice site point mutations have also been reported that result in protein truncation or internal deletion. The various types of mutations are associated with a rather homogeneous phenotype, and no obvious genotype-phenotype correlation can be identified. Both truncating and missense mutations appear to prevent secretion of mutant proteins, suggesting a loss of function effect of mutations. The function of LGI1 is unclear. Several molecular mechanisms possibly leading to lateral temporal epilepsy are illustrated and briefly discussed.

Genetic basis in epilepsies caused by malformations of cortical development and in those with structurally normal brain

Epilepsy is the most common neurological disorder affecting young people. The etiologies are multiple and most cases are sporadic. However, some rare families with Mendelian inheritance have provided evidence of genes' important role in epilepsy. Two important but apparently different groups of disorders have been extensively studied: epilepsies associated with malformations of cortical development (MCDs) and epilepsies associated with a structurally normal brain (or with minimal abnormalities only). This review is focused on clinical and molecular aspects of focal cortical dysplasia, polymicrogyria, periventricular nodular heterotopia, subcortical band heterotopia, lissencephaly and schizencephaly as examples of MCDs. Juvenile myoclonic epilepsy, childhood absence epilepsy, some familial forms of focal epilepsy and epilepsies associated with febrile seizures are discussed as examples of epileptic conditions in (apparently) structurally normal brains.

Altered language processing in autosomal dominant partial epilepsy with auditory features

BACKGROUND

Autosomal dominant partial epilepsy with auditory features (ADPEAF) is an idiopathic focal epilepsy syndrome with auditory symptoms or receptive aphasia as major ictal manifestations, frequently associated with mutations in the leucine-rich, glioma inactivated 1 (LGI1) gene. Although affected subjects do not have structural abnormalities detected on routine MRI, a lateral temporal malformation was identified through high resolution MRI in one family. We attempted to replicate this finding and to assess auditory and language processing in ADPEAF using fMRI and magnetoencephalography (MEG).

METHODS

We studied 17 subjects (10 affected mutation carriers, 3 unaffected carriers, 4 noncarriers) in 7 ADPEAF families, each of which had a different LGI1 mutation. Subjects underwent high-resolution structural MRI, fMRI with an auditory description decision task (ADDT) and a tone discrimination task, and MEG. A control group comprising 26 volunteers was also included.

RESULTS

We found no evidence of structural abnormalities in any of the 17 subjects. On fMRI with ADDT, subjects with epilepsy had significantly less activation than controls. On MEG with auditory stimuli, peak 2 auditory evoked field latency was significantly delayed in affected individuals compared to controls.

CONCLUSIONS

These findings do not support the previous report of a lateral temporal malformation in autosomal dominant partial epilepsy with auditory features (ADPEAF). However, our fMRI and magnetoencephalography data suggest that individuals with ADPEAF have functional impairment in language processing.

Penetrance of LGI1 mutations in autosomal dominant partial epilepsy with auditory features

BACKGROUND

Assessment of the penetrance of disease-causing mutations is extremely important for developing clinical applications of gene discovery, such as genetic testing and counseling. Mutations in the leucine-rich, glioma inactivated 1 gene (LGI1) have been identified in about 50% of families with autosomal dominant partial epilepsy with auditory features (ADPEAF), but estimates of LGI1 mutation penetrance have ranged widely, from 50 to 85%. The current study aimed to provide a more precise estimate of LGI1 mutation penetrance.

METHODS

We analyzed data from all 24 previously published ADPEAF families with mutations in LGI1. To estimate penetrance, we used the information from the published pedigree figures to determine the proportion of obligate carriers who were affected. We assessed whether penetrance was associated with the total number of affected individuals in each family, or mutation type (truncating or missense) or location within the gene. We also compared penetrance in males and females, and among different generations within the families.

RESULTS

Overall penetrance was 67% (95% CI 55-77%), and did not vary according to mutation type or location within the gene. Penetrance was greater in families with more affected individuals, but this trend was not significant. Penetrance did not differ by gender but increased with advancing generation, probably because of limited information about early generations.

CONCLUSIONS

Our results suggest that about two-thirds of individuals who inherit a mutation in LGI1 will develop epilepsy. This probably overestimates the true penetrance in the population because it is based on data from families containing multiple affected individuals.

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.

Expression profile of Lgi1 gene in mouse brain during development

Mutations in LGI1 were described in patients with autosomal dominant partial epilepsy with auditory features (ADPEAF), and recent clinical findings have implicated LGI1 in human brain development. However, the precise role of LGI1 in epileptogenesis remains largely unknown. The objective of this study was to determine the expression pattern of Lgi1 in mice brain during development and in adult animals. Real-time polymerase chain reaction (PCR) quantification and Western blot experiments showed a relative low expression during intrauterine stages, increasing until adulthood. In addition, we did not find significant differences between left and right hemispheres. The hippocampus presented higher levels of Lgi1 expression when compared to the neocortex and the cerebellum of adult animals; however, these results did not reach statistical significance. This study was the first to determine a specific profile of Lgi1 gene expression during central nervous system development, which suggests a possible inhibitory function in latter stages of development. In addition, we did not find differences in hemispheric expression that could explain the predominance of left-sided abnormalities in patients with ADPEAF.

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.

The genetics of temporal lobe epilepsy and implications for treatment

Temporal Lobe Epilepsy and GEFS+ Phenotypes Associated with SCN1B Mutations. Scheffer IE, Harkin LA, Grinton BE, Dibbens LM, Turner SJ, Zielinski MA, Xu R, Jackson G, Adams J, Connellan M, Petrou S, Wellard RM, Briellmann RS, Wallace RH, Mulley JC, Berkovic SF. Brain 2007;130(Pt 1):100–109. SCN1B, the gene encoding the sodium channel β1 subunit, was the first gene identified for generalized epilepsy with febrile seizures plus (GEFS+). Only three families have been published with SCN1B mutations. Here, we present four new families with SCN1B mutations and characterize the associated phenotypes. Analysis of SCN1B was performed on 402 individuals with various epilepsy syndromes. Four probands with missense mutations were identified. Detailed electroclinical phenotyping was performed on all available affected family members including quantitative MR imaging in those with temporal lobe epilepsy (TLE). Two new families with the original C121W SCN1B mutation were identified; novel mutations R85C and R85H were each found in one family. The following phenotypes occurred in the six families with SCN1B missense mutations: 22 febrile seizures, 20 febrile seizures plus, five TLE, three other GEFS+ phenotypes, two unclassified and ten unaffected individuals. All individuals with confirmed TLE had the C121W mutation; two underwent temporal lobectomy (one with hippocampal sclerosis and one without) and both are seizure free. We confirm the role of SCN1B in GEFS+ and show that the GEFS+ spectrum may include TLE alone. TLE with an SCN1B mutation is not a contraindication to epilepsy surgery.

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.

A method for estimating penetrance from families sampled for linkage analysis

When a gene variant is discovered to segregate with a disease, it may be of interest to estimate the risk (or the age-specific risk) of the disease to carriers of the variant. The families that contributed to the discovery of the variant would typically contain multiple carriers, and so, especially if the variant is rare, might prove a valuable source of study subjects for estimation of the risk. These families, by virtue of having brought the gene in question to the attention of researchers, however, may not be representative of the relationship between carrier status and the risk of the disease in the population. Using these families for risk estimation could bias the observed association between the variant and the risk. The purpose here is to present an approach to adjusting for the potential bias while using the families from linkage analysis to estimate the risk.

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.

LRRC4 controls in vitro invasion of glioblastoma cells through inhibiting RPTP-zeta expression

LRRC4 (leucine rich repeat containing 4), a novel member of LRP (Leucine-rich repeat protein) superfamily, contains a conserved leucine-rich repeat (LRR) cassette and an immunoglobulin-like (IgC2) domain in its extracellular region. In the present study, we demonstrated that the N and C terminal LRR (LRRNT and LRRCT) are requisite for membrane and cytoplasm location of LRRC4 in Cos7 cells. We also suggested that RPTP-zeta (receptor-type protein tyrosine phosphatase) receptor is relevant to the invasion ability of gliomas cells, and its expression is inhibited by the reexpression of LRRC4. Our observations indicated that LRRC4 may be a negative regulator of the RPTP-zeta receptor, and contribute to suppressing the invasion ability of gliomas cells.

Genetic analysis of the LGI/Epitempin gene family in sporadic and familial lateral temporal lobe epilepsy

Mutations in the LGI1/Epitempin gene cause autosomal dominant lateral temporal lobe epilepsy (ADLTE), a partial epilepsy characterized by the presence of auditory seizures. However, not all the pedigrees with a phenotype consistent with ADLTE show mutations in LGI1/Epitempin, or evidence for linkage to the 10q24 locus. Other authors as well as ourselves have found an internal repeat (EPTP, pfam# PF03736) that allowed the identification of three other genes sharing a sequence and structural similarity with LGI1/Epitempin. In this work, we present the sequencing of these genes in a set of ADLTE families without mutations in both LGI1/Epitempin and sporadic cases. No analyzed polymorphisms modified susceptibility in either the familial or sporadic forms of this partial epilepsy.

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.

Expression studies in gliomas and glial cells do not support a tumor suppressor role for LGI1

Disruptions of LGI1 in glioblastoma (GBM) cell lines and LGI1 mutations in families with autosomal dominant epilepsy imply a role for LGI1 in glial cells as well as in neurons. Although we and others could not find LGI1 mutations in malignant gliomas, our initial studies appeared to support the idea that LGI1 is poorly expressed or absent in these tumors. Microarray data suggested that LGI1 could be involved in the control of matrix metalloproteinases, and we found that tumors derived from U87 glioblastoma cells overexpressing LGI1 were less aggressive than U87 control tumors. To our surprise, we observed that LGI1 expression after differentiation of murine neural stem cells was robust in neurons but negligible in glial cells, in agreement with immunohistochemistry studies on rodent brain. This observation could suggest that the variable levels of LGI1 expression in gliomas reflect the presence of neurons entrapped within the tumor. To test this hypothesis, we investigated LGI1 expression in parallel with expression of the neuronal marker NEF3 by real-time PCR on 30 malignant gliomas. Results showed a strong, positive correlation between the expression levels of these two genes (P < 0.0001). Thus, our data confirm that LGI1 is involved in cell-matrix interactions but suggest that its expression is not relevant in glial cells, implying that its role as a tumor suppressor in gliomas should be reconsidered.

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.

Genetic Focal Epilepsies: State of the Art and Paths to the Future

The concept of genetic focal epilepsies is relatively new as compared to awareness of the importance of genetic factors in the generalized epilepsies. However, in the past decade, there has been increasing recognition of families with dominantly inherited partial epilepsies. Better definition of the phenotypes allows identification of distinct syndromes. The main familial focal epilepsies are autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE), familial mesial TLE (FMTLE), familial lateral TLE (FLTLE), and familial partial epilepsy with variable foci (FPEVF). The only genes identified so far are those for ADNFLE and FLTLE. In these disorders, functional studies are the next step and could provide advances leading to clarification of the pathophysiology as well as to new therapeutic strategies. At present, we can provide genetic counseling and a more accurate prognosis for most of the familial focal epilepsies. Greater awareness of the genetic basis in this group of disorders by the treating physicians is essential for identification of new families. This will allow further linkage studies, candidate gene screening, and identification of new genes, which will hopefully result in genetically based prevention and treatment.

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.

Canine epilepsy: what can we learn from human seizure disorders?

Epilepsy is a common neurological disorder in both dogs and humans. It is refractory to therapy in approximately one-third of canine patients, and even with the advent of new antiepileptic drugs for humans, appropriate treatment options in dogs remain limited. The pathogenesis and pathophysiology of epilepsy is being studied extensively in both human patients and rodent models of experimental epilepsy at the cellular and molecular level, but very little is known about the aetiologies of epilepsies in dogs. In this review, canine epilepsy will be discussed with reference to the human epilepsies and experimental epilepsy research. There is much work to be done in order to classify canine seizure types and breed-specific epileptic syndromes, particularly with reference to electroencephalographic abnormalities and possible genetic abnormalities. The review considers the appropriate use of antiepileptic drugs: phenobarbitone and potassium bromide are effective in most canine patients, although dosing regimes need to be carefully tailored to the individual, with serum concentration measurement. However, a significant proportion of patients remains refractory to these drugs. Work is currently underway to test the efficacy of newer antiepileptic drugs in the treatment of canine epilepsy, and preliminary data suggest that human drugs such as levetiracetam and gabapentin are of benefit in dogs with refractory epilepsy.

Sacred disease secrets revealed: the genetics of human epilepsy

Neurons throughout the brain suddenly discharging synchronously and recurrently cause primarily generalized seizures. Discharges localized awhile in one part of the brain cause focal-onset seizures. A genetically determined generalized hyperexcitability had been predicted in primarily generalized seizures, but surprisingly the first epilepsy gene discovered, CHRNA4, was in a focal (frontal lobe)-onset syndrome. Another surprise with CHRNA4 was its encoding of an ion channel present throughout the brain. The reason why CHRNA4 causes focal-onset seizures is unknown. Recently, the second focal (temporal lobe)-onset epilepsy gene, LGI1 (unknown function), was discovered. CHRNA4 led the way to mutation identifications in 15 ion channel genes, most causing primarily generalized epilepsies. Potassium channel mutations cause benign familial neonatal convulsions. Sodium channel mutations cause generalized epilepsy with febrile seizures plus or, if more severe, severe myoclonic epilepsy of infancy. Chloride and calcium channel mutations are found in rare families with the common syndromes childhood absence epilepsy and juvenile myoclonic epilepsy (JME). Mutations in the EFHC1 gene (unknown function) occur in other rare JME families, and yet in other families, associations are present between JME (or other generalized epilepsies) and single nucleotide polymorphisms in the BRD2 gene (unknown function) and the malic enzyme 2 (ME2) gene. Hippocrates predicted the genetic nature of the 'sacred' disease. Genes underlying the 'malevolent' forces seizing 1% of humans have now been revealed. These, however, still account for a mere fraction of the genetic contribution to epilepsy. Exciting years are ahead, in which the genetics of this extremely common, and debilitating, neurological disorder will be solved.

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.

Isolated idiopathic hypomagnesemia presenting as aphasia and seizures

Isolated hypomagnesemia of the idiopathic form is a rare condition that is known to present as generalized motor seizures in children. This report describes a 4-year-old African-American male who presented with a predominant symptom of sudden onset aphasia and no clear initial motor seizure activity. An evaluation revealed an isolated and severe hypomagnesemia (initial serum magnesium levels <1.0 mg/dL) and inappropriate renal handling of magnesium (fractional excretion of magnesium >40% under conditions of hypomagnesemia). The child had subsequent generalized tonic-clonic seizures that were brought under control with valproic acid therapy and magnesium supplementation. Six months after the diagnosis, he had regained 50-60% of his speech and had no further staring spells or motor seizure activity after the initial episode. Isolated and idiopathic hypomagnesemia caused by defective renal reabsorption of magnesium is a rare familial condition with variable inheritance. Aphasia as the solitary presenting symptom has not been described before. The exact pathophysiology of hypomagnesemic aphasia and seizures is not known but may relate to disinhibition of specific types of glutamate receptors. In the present case, neuronal depolarization may have been localized to language areas in the temporal lobes.

Speech-induced Aphasic Seizures in Epilepsy Caused by LGI1 Mutation

PURPOSE

Patients with autosomal dominant lateral temporal lobe epilepsy (ADTLE) may have seizures precipitated by sound or speech. We have examined a patient with speech-induced seizures caused by an LGI1 mutation (C46R).

METHODS

A clinical study and a video-EEG recording using interrogative speech as the activation procedure was performed in a 23-year-old man.

RESULTS

He had experienced short episodes of sensory aphasia in situations in which he was suddenly verbally addressed. Voices became distorted, and he could not comprehend despite hearing words. The day after a late party, his girlfriend unexpectedly spoke to him. Her speech became unintelligible to him. He did not reply and had a generalized tonic-clonic (GTC) seizure. During an EEG, he was suddenly asked for the names of his siblings. He answered, but lost understanding of the further conversation and described how syllables floated together with an echoing character. With a versive movement to the right, another GTC occurred. In the EEG, rhythmic 6-Hz activity built up in the frontotemporal areas starting on the left side with bilateral and posterior spreading. Postictal slowing was symmetrical, and no aphasia was noted on awakening.

CONCLUSIONS

To our knowledge, this is the first video-EEG recorded seizure in LGI1-caused ADTLE. This peculiar seizure semiology and precipitating effect of speech may serve as a marker for identifying further individuals with this particular phenotype and genotype and may indicate that the LGI1 gene may have a physiologic function connected to the human capacity for speech and language.

ADPEAF mutations reduce levels of secreted LGI1, a putative tumor suppressor protein linked to epilepsy

Mutations in LGI1 have been linked to autosomal dominant partial epilepsy with auditory features (ADPEAF), an unusual inherited human partial epilepsy phenotype. In addition, decreases in LGI1 expression are observed in glioblastoma patient samples and glioblastoma cell lines. LGI1, one member of the LGI gene family, encodes a approximately 63 kDa protein, with strong regional expression in neurons within the temporal lobe. Although the function of LGI proteins remains unknown, structural analyses suggest that LGI1 could be either localized to the membrane or secreted. Here, we show that LGI1-4 exhibit overlapping patterns of diffuse mRNA expression in the adult mouse brain, with some areas of specific localization characteristic of each family member. We find robust secretion of mouse LGI1 protein following transfection into 293T cells. LGI family members, LGI3, LGI4 and a newly identified splice form of LGI2, LGI2B, are also secreted in culture, indicating that secretion is a conserved feature of this protein family. Introduction of mutations in LGI1, including those identified in ADPEAF pedigrees, reveals that the mutant proteins either are not secreted or are unstable. These results demonstrate loss-of-function as a pathogenic basis for LGI1-mediated ADPEAF.

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.

LGI1 gene mutation screening in sporadic partial epilepsy with auditory features

Partial epilepsy with auditory features occasionally segregates in families as an autosomal dominant trait. In some families mutations in the leucine-rich glioma inactivated (LGI1) gene have been identified. Sporadic cases might harbour either denovo or low-penetrant LGI1 mutations, which will substantially alter the family risk for epilepsy. We selected sixteen sporadic patients with cryptogenic temporal lobe epilepsy and partial seizures with auditory features. We compared clinical features of these patients with those of published autosomal dominant family cases. We screened these patients for LGI1 mutations. Comparing the sporadic patients with the published familial cases no difference in either the primary auditory features or in the other associated epileptic manifestations was identified. Sequence analysis of the whole LGI1 gene coding regions in sporadic patients did not reveal changes in the LGI1 gene. The genetic analysis demonstrates that LGI1 is not a major gene for sporadic cases of partial epilepsy with auditory features at least in the Italian population. Screening of sporadic patients for LGI1 mutations appears not useful in genetic counselling of these patients.

Clinical and genetic aspects of idiopathic epilepsies in childhood

The identification of the first genes associated with idiopathic epilepsy has been an important breakthrough in the field of epilepsy research. In almost all cases these genes were found to encode components of voltage- or ligand-gated ion channels or functionally related structures. For many other idiopathic syndromes, there is linkage evidence to one or more chromosomes, but the genes have not yet been identified. Identification of the responsible genes and their gene products will further increase the knowledge of the pathogenic mechanisms involved in epilepsy, and will hopefully facilitate the development of drug targets for the effective treatment of epilepsy. This review gives an overview of the clinical characteristics and an update of genetic research of those idiopathic childhood epilepsies for which genes have been identified and the monogenic idiopathic childhood epilepsies for which mapping data are available.

Basic mechanisms of partial epilepsies

PURPOSE OF REVIEW

Partial epilepsies are characterized by cell loss with consequences for neuronal organization, excitability, mnestic and cognitive functions and present with pharmaco-resistance and difficulties in clinical management. While mesial temporal lobe epilepsies present frequently with cell loss and neuronal reorganization, neocortical epilepsies frequently involve developmental alterations.

RECENT FINDINGS

There is increasing evidence that nerve cells in epileptic tissue become more vulnerable to excitotoxic cell death due to impairment of mitochondrial functions and that free radical formation is critically involved in these processes. Whether and to what extent such alterations contribute to pharmaco-resistance is unclear. However, at least three mechanisms may contribute to pharmaco-resistance: changes in target molecules for antiepileptic drugs, upregulation of drug transporters, and potentially reorganization processes in inhibitory networks. Upregulation of drug transporters also seems to be involved in pharmaco-resistance of developmental alterations underlying focal epilepsies. Recent data from the literature suggest that transgenic models for disturbances of cortical development may be useful models for the study of these variable forms of partial epilepsies.

SUMMARY

The data suggest that improvement of therapy could result from free radical scavenging and from manipulation of drug transport into the affected tissue. New models of developmental epilepsies may help us to understand mechanisms underlying increased vulnerability to seizures as well as improving strategies for treatment.

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.

Fever, genes, and epilepsy

About 13% of patients with epilepsy have a history of febrile seizures (FS). Studies of familial forms suggest a genetic component to the epidemiological link. Indeed, in certain monogenic forms of FS, for which several loci have been reported, some patients develop epilepsy with a higher risk than in the general population. Patients with generalised epilepsy with febrile seizures plus (GEFS+) can have typical and isolated FS, FS lasting more beyond age 6 years, and subsequent afebrile (typically generalised) seizures. Mutations associated with GEFS+ were identified in genes for subunits of the voltage-gated sodium channel and the gamma2 subunit of the ligand-gated GABAA receptor. Screening for these genes in patients with severe myoclonic epilepsy in infancy showed de novo mutations of the alpha1 subunit of the voltage-gated sodium channel. Antecedent FS are commonly observed in temporal-lobe epilepsy (TLE). In sporadic mesial TLE-characterised by the sequence of complex FS in childhood, hippocampal sclerosis, and refractory temporal-lobe seizures-association studies suggested the role of several susceptibility genes. Work on some large pedigrees also suggests that FS and temporal-lobe seizures may have a common genetic basis, whether hippocampus sclerosis is present or not. The molecular defects identified in the genetic associations of FS and epileptic seizures are very attractive models to aid our understanding of epileptogenesis and susceptibility to seizure-provoking factors, especially fever.

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.

Idiopathic partial epilepsy with auditory features (IPEAF): a clinical and genetic study of 53 sporadic cases

The purpose of our study was to describe the clinical characteristics of sporadic (S) cases of partial epilepsy with auditory features (PEAF) and pinpoint clinical, prognostic and genetic differences with respect to previously reported familial (F) cases of autosomal dominant partial epilepsy with auditory features (ADPEAF). We analysed 53 patients (24 females and 29 males) with PEAF diagnosed according to the following criteria: partial epilepsy with auditory symptoms, negative family history for epilepsy and absence of cerebral lesions on NMR study. All patients underwent a full clinical, neuroradiological and neurophysiological examination. Forty patients were screened for mutations in LGI1/epitempin, which is involved in ADPEAF. Age at onset ranged from 6 to 39 years (average 19 years). Secondarily generalized seizures were the most common type of seizures at onset (79%). Auditory auras occurred either in isolation (53%) or associated with visual, psychic or aphasic symptoms. Low seizure frequency at onset and good drug responsiveness were common, with 51% of patients seizure-free. Seizures tended to recur after drug withdrawal. Clinically, no major differences were found between S and F patients with respect to age at onset, seizure frequency and response to therapy. Analysis of LGI1/epitempin exons failed to disclose mutations. Our data support the existence of a peculiar form of non-lesional temporal lobe epilepsy closely related to ADPEAF but without a positive family history. This syndrome, here named IPEAF, has a benign course in the majority of patients and could be diagnosed by the presence of auditory aura. Although LGI1 mutations have been excluded, genetic factors may play an aetiopathogenetic role in at least some of these S cases.

LGI1mutations in temporal lobe epilepsies

BACKGROUND AND OBJECTIVES

A number of familial temporal lobe epilepsies (TLE) have been recently recognized. Mutations in LGI1 (leucine-rich, glioma-inactivated 1 gene) have been found in a few families with the syndrome of autosomal dominant partial epilepsy with auditory features (ADPEAF). The authors aimed to determine the spectrum of TLE phenotypes with LGI1 mutations, to study the frequency of mutations in ADPEAF, and to examine the role of LGI1 paralogs in ADPEAF without LGI1 mutations.

METHODS

The authors performed a clinical and molecular analysis on 75 pedigrees comprising 54 with a variety of familial epilepsies associated with TLE and 21 sporadic TLE cases. All were studied for mutations in LGI1. ADPEAF families negative for LGI1 mutations were screened for mutations in LGI2, LGI3, and LGI4.

RESULTS

Four families had ADPEAF, 22 had mesial TLE, 11 had TLE with febrile seizures, two had TLE with developmental abnormalities, and 15 had various other TLE syndromes. LGI1 mutations were found in two of four ADPEAF families, but in none of the other 50 families nor in the 21 individuals with sporadic TLE. The mutations were novel missense mutations in exons 1 (c.124T-->G; C42G) and 8 (c.1418C-->T; S473L). No mutations in LGI2, LGI3, or LGI4 were found in the other two ADPEAF families.

CONCLUSION

In TLE, mutations in LGI1 are specific for ADPEAF but do not occur in all families. ADPEAF is genetically heterogeneous, but mutations in LGI2, LGI3, or LGI4 did not account for families without LGI1 mutations.

Monogenic idiopathic epilepsies

Major advances have recently been made in our understanding of the genetic bases of monogenic inherited epilepsies. Direct molecular diagnosis is now possible in numerous inherited symptomatic epilepsies. Progress has also been spectacular with respect to several idiopathic epilepsies that are caused by mutations in genes encoding subunits of ion channels or neurotransmitter receptors. Although these findings concern only a few families and sporadic cases, their potential importance is great, because these genes are implicated in a wide range of more common epileptic disorders and seizure types as well as some rare syndromes. Functional studies of these mutations, while leading to further progress in the neurobiology of the epilepsies, will help to refine genotype-phenotype relations and increase our understanding of responses to antiepileptic drugs. In this article, we review the clinical and genetic data on most of the idiopathic human epilepsies and epileptic contexts in which the association of epilepsy and febrile convulsions is genetically determined.

Autosomal Dominant Lateral Temporal Epilepsy: Two Families with Novel Mutations in the LGI1 Gene

PURPOSE

Mutations in the leucine rich, glioma inactivated gene (LGI1) were recently described in a small number of families with autosomal dominant lateral temporal epilepsy (ADLTE). ADLTE is characterized by partial seizures with symptoms suggestive of a lateral temporal onset, including frequent auditory aura. Here we report the results of clinical and genetic analyses of two newly identified families with ADTLE.

METHODS

We identified two families whose seizure semiology was suggestive of ADLTE. Evaluation included a detailed history and neurologic examination, as well as collection of DNA. The coding sequence of the LGI1 gene from affected subjects from both families was analyzed for evidence of mutation.

RESULTS

Each patient had a history of partial seizures, often with secondary generalization earlier in the course. Auditory aura was reported by approximately two thirds of affected patients in each pedigree. Novel mutations in LGI1 were detected in both families. A heterozygous single-nucleotide deletion at position 329 (del 329C) was detected in affected individuals from one family, whereas patients from the second family had a nonsynonymous variation, corresponding to C435G.

CONCLUSIONS

We identified two novel mutations in the LGI1 gene. The phenotype of these two families was similar to that of other kindreds with ADLTE, as auditory aura was absent in one third of affected individuals. Our results further support that LGI1 mutations should be considered in patients with a history of partial seizures if the semiology of seizures is consistent with the onset in the lateral temporal lobe.