LGI1 mutations in autosomal dominant and sporadic lateral temporal epilepsy

Molecular and cellular mechanisms underlying anti-neuronal antibody mediated disorders of the central nervous system

Over the last decade multiple autoantigens located on the plasma membrane of neurons have been identified. Neuronal surface antigens include molecules directly involved in neurotransmission and excitability. Binding of the antibody to the antigen may directly alter the target protein's function, resulting in neurological disorders. The often striking reversibility of symptoms following early aggressive immunotherapy supports a pathogenic role for autoantibodies to neuronal surface antigens. In order to better understand and treat these neurologic disorders it is important to gain insight in the underlying mechanisms of antibody pathogenicity. In this review we discuss the clinical, circumstantial, in vitro and in vivo evidence for neuronal surface antibody pathogenicity and the possible underlying cellular and molecular mechanisms. This review shows that antibodies to neuronal surface antigens are often directed at conformational epitopes located in the extracellular domain of the antigen. The conformation of the epitope can be affected by specific posttranslational modifications. This may explain the distinct clinical phenotypes that are seen in patients with antibodies to antigens that are expressed throughout the brain. Furthermore, it is likely that there is a heterogeneous antibody population, consisting of different IgG subtypes and directed at multiple epitopes located in an immunogenic region. Binding of these antibodies may result in different pathophysiological mechanisms occurring in the same patient, together contributing to the clinical syndrome. Unraveling the predominant mechanism in each distinct antigen could provide clues for therapeutic interventions.

Autosomal dominant partial epilepsy with auditory features: a new locus on chromosome 19q13.11-q13.31

OBJECTIVE

To clinically and genetically characterize a large Brazilian family with autosomal dominant partial epilepsy with auditory features (ADPEAF) not related to leucine-rich, glioma-inactivated 1 (LGI1) gene.

METHODS

Seventy family members (four married-ins) participating in the study were assessed by a detailed clinical interview and a complete neurologic examination. Genetic mapping was conducted through autosome-wide single nucleotide polymorphism (SNP) genotyping and subsequent linkage analysis on 16 and haplotype analysis on 25 subjects, respectively.

RESULTS

The pedigree comprised 15 affected members, of whom 11 were included in the study (male/female: 6/5; mean age 39.5 years). All but two (III:22 and IV:92) had focal seizures with auditory aura followed by secondary generalization in 44.4%. The mean age at onset of epilepsy seizures was 13.7 years. Initial autosome-wide SNP linkage analysis conducted on 12 subjects (8 affected) pointed to a single genomic region on chromosome 19 with a maximum multipoint logarithm of the odds (LOD) score of 2.60. Further refinement of this region through SNP and microsatellite genotyping on 16 subjects (11 affected) increased the LOD score to 3.41, thereby establishing 19q13.11-q13.31 as a novel ADPEAF locus. Haplotype analysis indicated that the underlying mutation is most likely located in a 9.74 Mb interval between markers D19S416 and D19S420. Sequence analysis of the most prominent candidate genes within this critical interval (SCN1B, LGI4, KCNK6, and LRFN1) did not reveal any mutation.

SIGNIFICANCE

This study disclosed a novel ADPEAF locus on chromosome 19q13.11-q13.31, contributing to future identification of a second dominant gene for this epileptic syndrome. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

Do neuronal autoantibodies cause psychosis? A neuroimmunological perspective

In the last decade, autoantibodies targeting proteins on the neuronal surface and that are believed to be directly pathogenic have been described in patients with autoimmune encephalitis. Since then, new antigenic targets have been discovered, and new clinical phenotypes have been recognized. The psychotic disorders are one example of this expanding spectrum. Here, we consider the defining criteria of antibody-mediated central nervous system disease and the extent to which the psychiatric data currently satisfy those criteria. We discuss the implications these findings have for our understanding, nosology, and treatment of psychiatric disorders.

Evaluation of seizure foci and genes in the Lgi1(L385R/+) mutant rat

Mutations in the leucine-rich, glioma inactivated 1 (LGI1) gene have been identified in patients with autosomal dominant lateral temporal lobe epilepsy (ADLTE). We previously reported that Lgi1 mutant rats, carrying a missense mutation (L385R) generated by gene-driven N-ethyl-N-nitrosourea (ENU) mutagenesis, showed generalized tonic-clonic seizures (GTCS) in response to acoustic stimuli. In the present study, we assessed clinically relevant features of Lgi1 heterozygous mutant rats (Lgi1(L385R/+)) as an animal model of ADLTE. First, to explore the focus of the audiogenic seizures, we performed electroencephalography (EEG) and brain Fos immunohistochemistry in Lgi1(L385R/+) and wild type rats. EEG showed unique seizure patterns (e.g., bilateral rhythmic spikes) in Lgi1(L385R/+) rats with GTCS. An elevated level of Fos expression indicated greater neural excitability to acoustic stimuli in Lgi1(L385R/+) rats, especially in the temporal lobe, thalamus and subthalamic nucleus. Finally, microarray analysis revealed a number of differentially expressed genes that may be involved in epilepsy. These results suggest that Lgi1(L385R/+) rats are useful as an animal model of human ADLTE.

What non-neuronal mechanisms should be studied to understand epileptic seizures?

While seizures ultimately result from aberrant firing of neuronal networks, several laboratories have embraced a non-neurocentric view of epilepsy to show that other cells in the brain also bear an etiologic impact in epilepsy. Astrocytes and brain endothelial cells are examples of controllers of neuronal homeostasis; failure of proper function of either cell type has been shown to have profound consequences on neurophysiology. Recently, an even more holistic view of the cellular and molecular mechanisms of epilepsy has emerged to include white blood cells, immunological synapses, the extracellular matrix and the neurovascular unit. This review will briefly summarize these findings and propose mechanisms and targets for future research efforts on non-neuronal features of neurological disorders including epilepsy.

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.

Suggestive linkage of familial mesial temporal lobe epilepsy to chromosome 3q26

PURPOSE

To describe the clinical findings in a family with a benign form of mesial temporal lobe epilepsy and to identify the causative genetic factors.

METHODS

All participants were personally interviewed and underwent neurologic examination. The affected subjects underwent EEG and most of them neuroradiological examinations (MRI). All family members were genotyped with the HumanCytoSNP-12 v1.0 beadchip and linkage analysis was performed with Merlin and Simwalk2 programs. Exome sequencing was performed on HiSeq2000, after exome capture with SureSelect 50 Mb kit v2.0.

RESULTS

The family had 6 members with temporal lobe epilepsy. Age at seizure onset ranged from 8 to 13 years. Five patients had epigastric auras often associated to oro-alimentary automatic activity, 3 patients presented loss of contact, and 2 experienced secondary generalizations. Febrile seizures occurred in 2 family members, 1 of whom also had temporal lobe epilepsy. EEG showed focal slow waves and epileptic abnormalities on temporal regions in 1 patient and was normal in the other affected individuals. MRI was normal in all temporal lobe epilepsy patients. We performed single nucleotide polymorphism-array linkage analysis of the family and found suggestive evidence of linkage (LOD score=2.106) to a region on chromosome 3q26. Haplotype reconstruction supported the linkage data and showed that the majority of unaffected family members carried the haplotype at risk. Whole exome sequencing failed to identify pathogenic mutations in genes of the candidate region.

CONCLUSIONS

Our data suggest the existence of a novel locus for benign familial mesial temporal lobe epilepsy on chromosome 3q26. Our failure to identify pathogenic mutations in genes of this region may be due to limitations of the exome sequencing technology.

Autoantibodies to epilepsy-related LGI1 in limbic encephalitis neutralize LGI1-ADAM22 interaction and reduce synaptic AMPA receptors

More than 30 mutations in LGI1, a secreted neuronal protein, have been reported with autosomal dominant lateral temporal lobe epilepsy (ADLTE). Although LGI1 haploinsufficiency is thought to cause ADLTE, the underlying molecular mechanism that results in abnormal brain excitability remains mysterious. Here, we focused on a mode of action of LGI1 autoantibodies associated with limbic encephalitis (LE), which is one of acquired epileptic disorders characterized by subacute onset of amnesia and seizures. We comprehensively screened human sera from patients with immune-mediated neurological disorders for LGI1 autoantibodies, which also uncovered novel autoantibodies against six cell surface antigens including DCC, DPP10, and ADAM23. Our developed ELISA arrays revealed a specific role for LGI1 antibodies in LE and concomitant involvement of multiple antibodies, including LGI1 antibodies in neuromyotonia, a peripheral nerve disorder. LGI1 antibodies associated with LE specifically inhibited the ligand-receptor interaction between LGI1 and ADAM22/23 by targeting the EPTP repeat domain of LGI1 and reversibly reduced synaptic AMPA receptor clusters in rat hippocampal neurons. Furthermore, we found that disruption of LGI1-ADAM22 interaction by soluble extracellular domain of ADAM22 was sufficient to reduce synaptic AMPA receptors in rat hippocampal neurons and that levels of AMPA receptor were greatly reduced in the hippocampal dentate gyrus in the epileptic LGI1 knock-out mouse. Therefore, either genetic or acquired loss of the LGI1-ADAM22 interaction reduces the AMPA receptor function, causing epileptic disorders. These results suggest that by finely regulating the synaptic AMPA receptors, the LGI1-ADAM22 interaction maintains physiological brain excitability throughout life.

A newly discovered LGI1 mutation in Korean family with autosomal dominant lateral temporal lobe epilepsy

PURPOSE

A new leucine-rich glioma-inactivated 1 gene (LGI1) mutation inducing an amino acid sequence substitution was found in a Korean family with autosomal dominant lateral temporal lobe epilepsy (ADLTE). We report the clinical features and characteristics of this newly identified LGI1 mutation.

METHODS

Clinical data were collected from a large ADLTE family. All exons and flanking regions of the LGI1 gene were directly sequenced. 243 healthy controls were screened for the putative mutation. The 'Sorting Tolerant From Intolerant' algorithm was employed for the prediction of mutated LGI1 protein stability. LGI1 protein secretion was confirmed in vitro by immunoblotting assay.

RESULTS

The main clinical characteristics included a young age at onset (mean, 12.4 years), diverse phenotypic manifestations, the occurrence of generalized tonic-clonic seizures, and a favorable prognosis. The genetic analysis detected a nonsynonymous single nucleotide polymorphism of c.137G>T coding for p.C46F in the five affected family members. This variant was not found in the normal control population and one unaffected family member. All the amino acids substituted for cysteine at position 46 of the LGI1 protein were predicted to damage protein stability in in silico analysis. Mutated C46F protein was retained within the cell at the immunoblotting assay.

CONCLUSION

We identified a new LGI1 mutation in a large Korean ADLTE family which appeared to be involved in the development of epilepsy through suppressing LGI1 protein secretion.

Seizure semiology in autosomal dominant epilepsy with auditory features, due to novel LGI1 mutations

Mutations in LGI1 are found in 50% of families with autosomal dominant epilepsy with auditory features (ADEAF). In ADEAF, family members have predominantly lateral temporal lobe seizures but mesial temporal lobe semiology may also occur. We report here three families with novel LGI1 mutations (p.Ile82Thr, p.Glu225*, c.432-2_436del). Seven affected individuals reported an auditory aura and one a visual aura. A 10-year old boy described a cephalic aura followed by an unpleasant taste and oral automatisms without auditory, visual or psychic features.

Targeting the neural extracellular matrix in neurological disorders

The extracellular matrix (ECM) is known to regulate important processes in neuronal cell development, activity and growth. It is associated with the structural stabilization of neuronal processes and synaptic contacts during the maturation of the central nervous system. The remodeling of the ECM during both development and after central nervous system injury has been shown to affect neuronal guidance, synaptic plasticity and their regenerative responses. Particular interest has focused on the inhibitory role of chondroitin sulfate proteoglycans (CSPGs) and their formation into dense lattice-like structures, termed perineuronal nets (PNNs), which enwrap sub-populations of neurons and restrict plasticity. Recent studies in mammalian systems have implicated CSPGs and PNNs in regulating and restricting structural plasticity. The enzymatic degradation of CSPGs or destabilization of PNNs has been shown to enhance neuronal activity and plasticity after central nervous system injury. This review focuses on the role of the ECM, CSPGs and PNNs; and how developmental and pharmacological manipulation of these structures have enhanced neuronal plasticity and aided functional recovery in regeneration, stroke, and amblyopia. In addition to CSPGs, this review also points to the functions and potential therapeutic value of these and several other key ECM molecules in epileptogenesis and dementia.

The molecular biology of genetic-based epilepsies

Epilepsy is one of the most common neurological disorders characterized by abnormal electrical activity in the central nervous system. The clinical features of this disorder are recurrent seizures, difference in age onset, type, and frequency, leading to motor, sensory, cognitive, psychic, or autonomic disturbances. Since the discovery of the first monogenic gene mutation in 1995, it is proposed that genetic factor plays an important role in the mechanism of epilepsy. Genes discovered in idiopathic epilepsies encode for ion channel or neurotransmitter receptor proteins, whereas syndromes with epilepsy as a main feature are caused by genes that are involved in functions such as cortical development, mitochondrial function, and cell metabolism. The identification of these monogenic epilepsy-causing genes provides new insight into the pathogenesis of epilepsies. Although most of the identified gene mutations present a monogenic inheritance, most of idiopathic epilepsies are complex genetic diseases exhibiting a polygenic or oligogenic inheritance. This article reviews recent genetic and molecular progresses in exploring the pathogenesis of epilepsy, with special emphasis on monogenic epilepsy-causing genes, including voltage-gated channels (Na(+), K(+), Ca(2+), Cl(-), and HCN), ligand-gated channels (nicotinic acetylcholine and GABAA receptors), non-ion channel genes as well as the mitochondrial DNA genes. These progresses have improved our understanding of the complex neurological disorder.

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.

Low penetrance of autosomal dominant lateral temporal epilepsy in Italian families without LGI1 mutations

PURPOSE

In relatively small series, autosomal dominant lateral temporal epilepsy (ADLTE) has been associated with leucine-rich, glioma-inactivated 1 (LGI1) mutations in about 50% of the families, this genetic heterogeneity being probably caused by differences in the clinical characteristics of the families. In this article we report the overall clinical and genetic spectrum of ADLTE in Italy with the aim to provide new insight into its nosology and genetic basis.

METHODS

In a collaborative study of the Commission of Genetics of the Italian League Against Epilepsy (LICE) encompassing a 10-year period (2000-2010), we collected 33 ADLTE families, selected on the basis of the following criteria: presence of at least two members concordant for unprovoked partial seizures with prominent auditory and or aphasic symptoms, absence of any known structural brain pathology or etiology, and normal neurologic examination. The clinical, neurophysiologic, and neuroradiologic findings of all patients were analyzed and a genealogic tree was built for each pedigree. The probands' DNA was tested for LGI1 mutations by direct sequencing and, if negative, were genotyped with single-nucleotide polymorphism (SNP) array to search for disease-linked copy-number variation CNV. The disease penetrance in mutated and nonmutated families was assessed as a proportion of obligate carriers who were affected.

KEY FINDINGS

The 33 families included a total of 127 affected individuals (61 male, 66 female, 22 deceased). The age at onset ranged between 2 and 60 years (mean 18.7 years). Ninety-one patients (72%) had clear-cut focal (elementary, complex, or secondarily generalized) seizures, characterized by prominent auditory auras in 68% of the cases. Other symptoms included complex visual hallucinations, vertigo, and déjà vu. Aphasic seizures, associated or not with auditory features, were observed in 20% of the cases, whereas tonic-clonic seizures occurred in 86% of the overall series. Sudden noises could precipitate the seizures in about 20% of cases. Seizures, which usually occurred at a low frequency, were promptly controlled or markedly improved by antiepileptic treatment in the majority of patients. The interictal electroencephalography (EEG) studies showed the epileptiform temporal abnormalities in 62% of cases, with a slight predominance over the left region. Magnetic resonance imaging (MRI) or computerized tomography (CT) scans were negative. LGI1 mutations (missense in nine and a microdeletion in one) were found in only 10 families (30%). The patients belonging to the mutated and not mutated groups did not differ except for penetrance estimate, which was 61.3% and 35% in the two groups, respectively (chi-square, p = 0.017). In addition, the disease risk of members of families with mutations in LGI1 was three times higher than that of members of LGI1-negative families (odds ratio [OR] 2.94, confidence interval [CI] 1.2-7.21).

SIGNIFICANCE

A large number of ADLTE families has been collected over a 10-year period in Italy, showing a typical and homogeneous phenotype. LGI1 mutations have been found in only one third of families, clinically indistinguishable from nonmutated pedigrees. The estimate of penetrance and OR, however, demonstrates a significantly lower penetrance rate and relative disease risk in non-LGI1-mutated families compared with LGI1-mutated pedigrees, suggesting that a complex inheritance pattern may underlie a proportion of these families.

Middle ear myoclonus: two informative cases and a systematic discussion of myogenic tinnitus

Background

The term middle ear myoclonus (MEM) has been invoked to explain symptoms of tinnitus presumably caused by the dysfunctional movement of either of the two muscles that insert in the middle ear: tensor tympani and stapedius. MEM has been characterized through heterogeneous case reports in the otolaryngology literature, where clinical presentation is variable, phenomenology is scarcely described, the pathogenic muscle is usually not specified, natural history is unknown, and the presumptive definitive treatment, tensor tympani or stapedius tendon lysis, is inconsistently effective. It is not surprising that no unique acoustogenic mechanism or pathophysiologic process has been identified to explain MEM, one of several descriptive diagnoses associated with the complicated disorders of myogenic tinnitus.

Methods

Here, we explore MEM from the neurologist’s perspective. Following the detailed descriptions of two informative cases from our clinic, we systematically evaluate the different mechanisms and movement disorder phenomena that could lead to a diagnosis of MEM.

Results

From a functional neuroanatomic perspective, we explain how tensor tympani MEM is best explained as a form of peritubal myogenic tinnitus, similar to the related disorder of essential palatal tremor. From a pathogenic perspective, we discuss how MEM symptomatology may reflect different mechanical and neurologic processes. We emphasize the diagnostic imperative to recognize when myogenic tinnitus is consistent with a psychogenic origin.

Discussion

Both individual patient care and further elucidation of MEM will rely on more detailed clinical characterization as well as multidisciplinary input from neurology, otolaryngology, and dentistry.

Genetics of epilepsy and relevance to current practice

Genetic factors are likely to play a major role in many epileptic conditions, spanning from classical idiopathic (genetic) generalized epilepsies to epileptic encephalopathies and focal epilepsies. In this review we describe the genetic advances in progressive myoclonus epilepsies, which are strictly monogenic disorders, genetic generalized epilepsies, mostly exhibiting complex genetic inheritance, and SCN1A-related phenotypes, namely genetic generalized epilepsy with febrile seizure plus and Dravet syndrome. Particular attention is devoted to a form of familial focal epilepsies, autosomal-dominant lateral temporal epilepsy, which is a model of non-ion genetic epilepsies. This condition is associated with mutations of the LGI1 gene, whose protein is secreted from the neurons and exerts its action on a number of targets, influencing cortical development and neuronal maturation.

Genetics of temporal lobe epilepsy

The most common partial epilepsy, temporal lobe epilepsy (TLE) consists of a heterogeneous group of seizure disorders originating in the temporal lobe. TLE had been thought to develop as a result of acquired structural problems in the temporal lobe. During the past two decades, there has been growing evidence of the important influence of genetic factors, and familial and non-lesional TLE have been increasingly described. Here, we focus on the genetics of TLE and review related genes which have been studied recently. Although its molecular mechanisms are still poorly understood, TLE genetics is a fertile field, awaiting more research.

A rat model for LGI1-related epilepsies

Mutations of the leucine-rich glioma-inactivated 1 (LGI1) gene cause an autosomal dominant partial epilepsy with auditory features also known as autosomal-dominant lateral temporal lobe epilepsy. LGI1 is also the main antigen present in sera and cerebrospinal fluids of patients with limbic encephalitis and seizures, highlighting its importance in a spectrum of epileptic disorders. LGI1 encodes a neuronal secreted protein, whose brain function is still poorly understood. Here, we generated, by ENU (N-ethyl-N-nitrosourea) mutagenesis, Lgi1-mutant rats carrying a missense mutation (L385R). We found that the L385R mutation prevents the secretion of Lgi1 protein by COS7 transfected cells. However, the L385R-Lgi1 protein was found at low levels in the brains and cultured neurons of Lgi1-mutant rats, suggesting that mutant protein may be destabilized in vivo. Studies on the behavioral phenotype and intracranial electroencephalographic signals from Lgi1-mutant rats recalled several features of the human genetic disorder. We show that homozygous Lgi1-mutant rats (Lgi1(L385R/L385R)) generated early-onset spontaneous epileptic seizures from P10 and died prematurely. Heterozygous Lgi1-mutant rats (Lgi1(+/L385R)) were more susceptible to sound-induced, generalized tonic-clonic seizures than control rats. Audiogenic seizures were suppressed by antiepileptic drugs such as carbamazepine, phenytoin and levetiracetam, which are commonly used to treat partial seizures, but not by the prototypic absence seizure drug, ethosuximide. Our findings provide the first rat model with a missense mutation in Lgi1 gene, an original model complementary to knockout mice. This study revealed that LGI1 disease-causing missense mutations might cause a depletion of the protein in neurons, and not only a failure of Lgi1 secretion.

LGI1 microdeletion in autosomal dominant lateral temporal epilepsy

OBJECTIVES

To characterize clinically and genetically a family with autosomal dominant lateral temporal epilepsy (ADLTE) negative to LGI1 exon sequencing test.

METHODS

All participants were personally interviewed and underwent neurologic examination. Most affected subjects underwent EEG and neuroradiologic examinations (CT/MRI). Available family members were genotyped with the HumanOmni1-Quad v1.0 single nucleotide polymorphism (SNP) array beadchip and copy number variations (CNVs) were analyzed in each subject. LGI1 gene dosage was performed by real-time quantitative PCR (qPCR).

RESULTS

The family had 8 affected members (2 deceased) over 3 generations. All of them showed GTC seizures, with focal onset in 6 and unknown onset in 2. Four patients had focal seizures with auditory features. EEG showed only minor sharp abnormalities in 3 patients and MRI was unremarkable in all the patients examined. Three family members presented major depression and anxiety symptoms. Routine LGI1 exon sequencing revealed no point mutation. High-density SNP array CNV analysis identified a genomic microdeletion about 81 kb in size encompassing the first 4 exons of LGI1 in all available affected members and in 2 nonaffected carriers, which was confirmed by qPCR analysis.

CONCLUSIONS

This is the first microdeletion affecting LGI1 identified in ADLTE. Families with ADLTE in which no point mutations are revealed by direct exon sequencing should be screened for possible genomic deletion mutations by CNV analysis or other appropriate methods. Overall, CNV analysis of multiplex families may be useful for identifying microdeletions in novel disease genes.

Natural history of temporal lobe epilepsy: antecedents and progression

Temporal lobe epilepsy represents the largest group of patients with treatment resistant/medically intractable epilepsy undergoing epilepsy surgery. The underpinnings of common forms of TLE in many instances begin in early life with the occurrence of an initial precipitating event. The first epileptic seizure often occurs after a variable latency period following this event. The precise natural history and progression following the first seizure to the development of TLE, its subsequent resolution through spontaneous remission or the development of treatment resistant epilepsy remain poorly understood. Our present understanding of the role played by these initial events, the subsequent latency to development of temporal lobe epilepsy, and the emergence of treatment resistance remains incomplete. A critical analysis of published data suggest that TLE is a heterogeneous condition, where the age of onset, presence or absence of a lesion on neuroimaging, the initial precipitating event, association with febrile seizures, febrile status epilepticus, and neurotropic viral infections influence the natural history and outcome. The pathways and processes through which these variables coalesce into a framework will provide the basis for an understanding of the natural history of TLE. The questions raised need to be addressed in future prospective and longitudinal observational studies.

Epilepsy gene LGI1 regulates postnatal developmental remodeling of retinogeniculate synapses

Retinogeniculate connections undergo postnatal refinement in the developing visual system. Here we report that non-ion channel epilepsy gene LGI1 (leucine-rich glioma-inactivated), mutated in human autosomal dominant lateral temporal lobe epilepsy (ADLTE), regulates postnatal pruning of retinal axons in visual relay thalamus. By introducing an ADLTE-associated truncated mutant LGI1 (836delC) or excess full-length LGI1 into transgenic mice, we found that mutant LGI1 blocks, whereas excess LGI1 accelerates, retinogeniculate axon pruning. The normal postnatal single fiber strengthening was arrested by mutant LGI1 and, contrastingly, was enhanced by excess wild-type LGI1. The maximum response of the retinogeniculate synapses, conversely, remained the same in mature LGI1 transgenic mice, indicating that mutant LGI1 blocks, whereas excess wild-type LGI1 promotes, weak axon fiber elimination. Heterozygous deletion of the LGI1 gene, as found in ADLTE patients, inhibited postnatal retinogeniculate synapse elimination, an effect similar to the ADLTE truncated mutant LGI1. The results identify sensory axon remodeling defects in a sensory aura-associated human epilepsy disorder.

Genetics of temporal lobe epilepsy: a review

Temporal lobe epilepsy (TLE) is usually regarded as a polygenic and complex disorder. To understand its genetic component, numerous linkage analyses of familial forms and association studies of cases versus controls have been conducted since the middle of the nineties. The present paper lists genetic findings for TLE from the initial segregation analysis to the most recent results published in May 2011. To date, no genes have been clearly related to TLE despite many efforts to do so. However, it is vital to continue replication studies and collaborative attempts to find significant results and thus determine which gene variant combination plays a definitive role in the aetiology of TLE.

Domain-dependent clustering and genotype-phenotype analysis of LGI1 mutations in ADPEAF

OBJECTIVE

In families with autosomal dominant partial epilepsy with auditory features (ADPEAF) with mutations in the LGI1 gene, we evaluated clustering of mutations within the gene and associations of penetrance and phenotypic features with mutation location and predicted effect (truncation or missense).

METHODS

We abstracted clinical and molecular information from the literature for all 36 previously published ADPEAF families with LGI1 mutations. We used a sliding window approach to analyze mutation clustering within the gene. Each mutation was mapped to one of the gene's 2 major functional domains, N-terminal leucine-rich repeats (LRRs) and C-terminal epitempin (EPTP) repeats, and classified according to predicted effect on the encoded protein (truncation vs missense). Analyses of phenotypic features (age at onset and occurrence of auditory symptoms) in relation to mutation site and predicted effect included 160 patients with idiopathic focal unprovoked seizures from the 36 families.

RESULTS

ADPEAF-causing mutations clustered significantly in the LRR domain (exons 3-5) of LGI1 (p = 0.026). Auditory symptoms were less frequent in individuals with truncation mutations in the EPTP domain than in those with other mutation type/domain combinations (58% vs 80%, p = 0.018).

CONCLUSION

The LRR region of the LGI1 gene is likely to play a major role in pathogenesis of ADPEAF.

Loss of zebrafish lgi1b leads to hydrocephalus and sensitization to pentylenetetrazol induced seizure-like behavior

Mutations in the LGI1 gene predispose to a hereditary epilepsy syndrome and is the first gene associated with this disease which does not encode an ion channel protein. In zebrafish, there are two paralogs of the LGI1 gene, lgi1a and lgi1b. Knockdown of lgi1a results in a seizure-like hyperactivity phenotype with associated developmental abnormalities characterized by cellular loss in the eyes and brain. We have now generated knockdown morphants for the lgi1b gene which also show developmental abnormalities but do not show a seizure-like behavior. Instead, the most striking phenotype involves significant enlargement of the ventricles (hydrocephalus). As shown for the lgi1a morphants, however, lgi1b morphants are also sensitized to PTZ-induced hyperactivity. The different phenotypes between the two lgi1 morphants support a subfunctionalization model for the two paralogs.

The genetics of monogenic idiopathic epilepsies and epileptic encephalopathies

The group of idiopathic epilepsies encompasses numerous syndromes without known organic substrate. Genetic anomalies are thought to be responsible for pathogenesis, with a monogenic or polygenic model of inheritance. Over the last two decades, a number of genetic anomalies and encoded proteins have been related to particular idiopathic epilepsies and epileptic encephalopathies. Most of these mutations involve subunits of neuronal ion channels (e.g. potassium, sodium, and chloride channels), and may result in abnormal neuronal hyperexcitability manifesting with seizures. However non-ion channel proteins may also be affected. Correlations between genotype and phenotype are not easy to establish, since genetic and non-genetic factors are likely to play a role in determining the severity of clinical features. The growing number of discoveries on this topic are improving classification, prognosis and counseling of patients and families with these forms of epilepsy, and may lead to targeted therapeutic approaches in the near future. In this article the authors have reviewed the main genetic discoveries in the field of the monogenic idiopathic epilepsies and epileptic encephalopathies, in order to provide epileptologists with a concise and comprehensive summary of clinical and genetic features of these seizure disorders.

GABBR1 gene polymorphism(G1465A)isassociated with temporal lobe epilepsy

PURPOSE

γ-Aminobutyric acid B receptor 1(GABBR1) gene G1465A polymorphism has been considered as a potential risk factor for the development of temporal lobe epilepsy (TLE). However, the results were inconsistent. In this study, we performed a meta-analysis to assess the association between GABBR1 G1465A polymorphism and the risk of TLE.

METHODS

Biomedical literature databases including PubMed, ISI web of science and Embase were searched. The studies evaluating the association between GABBR1 G1465A polymorphism and TLE were included. Pooled odds ratio (OR) and 95%CI confidence interval (CI) were calculated using fixed- or random-effects model.

KEY FINDINGS

Seven studies (1011 cases and 2184 controls) met the inclusion criteria and were included in the meta-analysis. The overall result showed that the association between GABBR1 G1465A polymorphism was statistically significant (OR=5.381, 95%CI: 1.726, 16.776, P=0.004). Subgroup analysis showed that the effect estimate was higher in the studies with high quality score (OR=14.220, 95%CI: 6.933, 29.169, P=0.000) than that in the studies with low quality score (OR=1.158, 95%CI: 0.325, 4.123, P=0.821).

SIGNIFICANCE

The present meta-analysis suggests that GABBR1 G1465A polymorphism is associated with the risk of TLE. The role of GABBR1 G1465A polymorphism in the development of TLE merits further investigation.

Genetic variations and associated pathophysiology in the management of epilepsy

The genomic era has enabled the application of molecular tools to the solution of many of the genetic epilepsies, with and without comorbidities. Massively parallel sequencing has recently reinvigorated gene discovery for the monogenic epilepsies. Recurrent and novel copy number variants have given much-needed impetus to the advancement of our understanding of epilepsies with complex inheritance. Superimposed upon that is the phenotypic blurring by presumed genetic modifiers scattering the effects of the primary mutation. The genotype-first approach has uncovered associated syndrome constellations, of which epilepsy is only one of the syndromes. As the molecular genetic basis for the epilepsies unravels, it will increasingly influence the classification and diagnosis of the epilepsies. The ultimate goal of the molecular revolution has to be the design of treatment protocols based on genetic profiles, and cracking the 30% of epilepsies refractory to current medications, but that still lies well into the future. The current focus is on the scientific basis for epilepsy. Understanding its genetic causes and biophysical mechanisms is where we are currently positioned: prizing the causes of epilepsy "out of the shadows" and exposing its underlying mechanisms beyond even the ion-channels.

LGI2 truncation causes a remitting focal epilepsy in dogs

One quadrillion synapses are laid in the first two years of postnatal construction of the human brain, which are then pruned until age 10 to 500 trillion synapses composing the final network. Genetic epilepsies are the most common neurological diseases with onset during pruning, affecting 0.5% of 2–10-year-old children, and these epilepsies are often characterized by spontaneous remission. We previously described a remitting epilepsy in the Lagotto romagnolo canine breed. Here, we identify the gene defect and affected neurochemical pathway. We reconstructed a large Lagotto pedigree of around 34 affected animals. Using genome-wide association in 11 discordant sib-pairs from this pedigree, we mapped the disease locus to a 1.7 Mb region of homozygosity in chromosome 3 where we identified a protein-truncating mutation in the Lgi2 gene, a homologue of the human epilepsy gene LGI1. We show that LGI2, like LGI1, is neuronally secreted and acts on metalloproteinase-lacking members of the ADAM family of neuronal receptors, which function in synapse remodeling, and that LGI2 truncation, like LGI1 truncations, prevents secretion and ADAM interaction. The resulting epilepsy onsets at around seven weeks (equivalent to human two years), and remits by four months (human eight years), versus onset after age eight in the majority of human patients with LGI1 mutations. Finally, we show that Lgi2 is expressed highly in the immediate post-natal period until halfway through pruning, unlike Lgi1, which is expressed in the latter part of pruning and beyond. LGI2 acts at least in part through the same ADAM receptors as LGI1, but earlier, ensuring electrical stability (absence of epilepsy) during pruning years, preceding this same function performed by LGI1 in later years. LGI2 should be considered a candidate gene for common remitting childhood epilepsies, and LGI2-to-LGI1 transition for mechanisms of childhood epilepsy remission.

Major remodeling of the neuronal synaptic network occurs during childhood. The quadrillion synapses formed till the end of age two are trimmed to 500 trillion by age 10 through a selective process of strengthening of ideal connections, removal of redundant ones, and formation of new contacts. Very little is known about the basic mechanisms that direct this massive reorganization that leads to the adult brain. The most common epilepsies of humans occur in childhood and are characterized by remission prior to adulthood. Not much is known about their genetics and basic remission mechanisms. We describe here a canine equivalent disease and identify the defective gene, Lgi2. We show that the gene product is a secreted protein and interacts with neuronal ADAM receptors known to be involved in the regulation of synaptic remodeling in the developing brain. Our work sheds important light on the basic mechanisms of the most common neurological disease of children and discloses processes of epilepsy remission. The identification of the first focal epilepsy gene in dogs has also enabled the development of a genetic test to identify carriers for breeding purposes.

Role of leucine-rich repeat proteins in the development and function of neural circuits

The nervous system consists of an ensemble of billions of neurons interconnected in a highly specific pattern that allows proper propagation and integration of neural activities. The organization of these specific connections emerges from sequential developmental events including axon guidance, target selection, and synapse formation. These events critically rely on cell-cell recognition and communication mediated by cell-surface ligands and receptors. Recent studies have uncovered central roles for leucine-rich repeat (LRR) domain-containing proteins, not only in organizing neural connectivity from axon guidance to target selection to synapse formation, but also in various nervous system disorders. Their versatile LRR domains, in particular, serve as key sites for interactions with a wide diversity of binding partners. Here, we focus on a few exquisite examples of secreted or membrane-associated LRR proteins in Drosophila and mammals and review the mechanisms by which they regulate diverse aspects of nervous system development and function.

Q8IYL2 is a candidate gene for the familial epilepsy syndrome of Partial Epilepsy with Pericentral Spikes (PEPS)

PURPOSE

Partial Epilepsy with Pericentral Spikes (PEPS) is a novel Mendelian idiopathic epilepsy with evidence of linkage to Chromosome 4p15. Our aim was to identify the causative mutation in this epilepsy syndrome.

METHODS

We re-annotated all 42 genes in the linked chromosomal region and sequenced all genes within the linked interval. All exons, intron-exon boundaries and untranslated regions were sequenced in the original pedigree, and novel changes segregating correctly were subjected to bioinformatic analysis. Quantitative polymerase chain reaction was performed to examine for potential copy number variation (CNV).

RESULTS

29 previously undescribed variants correctly segregating with the linked haplotype were identified. Bioinformatic analysis demonstrated that six variants were non-synonymous coding sequence polymorphisms, one of which, in Q8IYL2 (Gly400Ala), was found in neither Caucasian (n=243) and ancestry-matched Brazilian (n=180) control samples, nor subjects from the 1000 Genome Project. No gene duplications or deletions were identified in the linked region.

DISCUSSION

We postulate that Q8IYL2 is a causative gene for PEPS, after exhaustive resequencing and bioinformatic analysis. The function of this gene is unknown, but it is expressed in brain tissue.

The temporal and spatial expression pattern of the LGI1 epilepsy predisposition gene during mouse embryonic cranial development

Background

Mutations in the LGI1 gene predispose to a rare, hereditary form of temporal epilepsy. Currently, little is known about the temporal and spatial expression pattern of Lgi1 during normal embryogenesis and so to define this more clearly we used a transgenic mouse line that expresses GFP under the control of Lgi1 cis-regulatory elements.

Results

During embryonic brain growth, high levels of Lgi1 expression were found in the surface ectoderm, the neuroepithelium, mesenchymal connective tissue, hippocampus, and sensory organs, such as eye, tongue, and the olfactory bulb. Lgi1 was also found in the cranial nerve nuclei and ganglia, such as vestibular, trigeminal, and dorsal ganglia. Expression of Lgi1 followed an orchestrated pattern during mouse development becoming more subdued in areas of the neocortex of the mid- and hind-brain in early postnatal animals, although high expression levels were retained in the choroid plexus and hippocampus. In late postnatal stages, Lgi1 expression continued to be detected in many areas in the brain including, hippocampus, paraventricular thalamic nuclei, inferior colliculus, and the cerebral aqueduct. We also showed that Lgi1-expressing cells co-express nestin, DCX, and beta-III tubulin suggesting that Lgi1-expressing cells are migratory neuroblasts.

Conclusion

These observations imply that Lgi1 may have a role in establishing normal brain architecture and neuronal functions during brain development suggesting that it may be involved in neurogenesis and neuronal plasticity, which become more specifically defined in the adult animal.

Low penetrance and effect on protein secretion of LGI1 mutations causing autosomal dominant lateral temporal epilepsy

PURPOSE

To describe the clinical and genetic findings of four families with autosomal dominant lateral temporal epilepsy.

METHODS

A personal and family history was obtained from each affected and unaffected subject along with a physical and neurologic examination. Routine electroencephalography and magnetic resonance imaging (MRI) studies were performed in almost all patients. DNAs from family members were screened for LGI1 mutations. The effects of mutations on Lgi1 protein secretion were determined in transfected culture cells.

KEY FINDINGS

The four families included a total of 11 patients (two deceased), six of whom had lateral temporal epilepsy with auditory aura. Age at onset was in the second decade of life; seizures were well controlled by antiepileptic treatment and MRI studies were normal. We found two pathogenic LGI1 mutations with uncommonly low penetrance: the R136W mutation, previously detected in a sporadic case with telephone-induced partial seizures, gave rise to the epileptic phenotype in three of nine mutation carriers in one family; the novel C179R mutation caused epilepsy in an isolated patient from a family where the mutation segregated. Another novel pathogenic mutation, I122T, and a nonsynonymous variant, I359V, were found in the two other families. Protein secretion tests showed that the R136W and I122T mutations inhibited secretion of the mutant proteins, whereas I359V had no effect on protein secretion; C179R was not tested, because of its predictable effect on protein folding.

SIGNIFICANCE

These findings suggest that some LGI1 mutations may have a weak penetrance in families with complex inheritance pattern, or isolated patients, and that the protein secretion test, together with other predictive criteria, may help recognize pathogenic LGI1 mutations.

A computational model of the LGI1 protein suggests a common binding site for ADAM proteins

Mutations of human leucine-rich glioma inactivated (LGI1) gene encoding the epitempin protein cause autosomal dominant temporal lateral epilepsy (ADTLE), a rare familial partial epileptic syndrome. The LGI1 gene seems to have a role on the transmission of neuronal messages but the exact molecular mechanism remains unclear. In contrast to other genes involved in epileptic disorders, epitempin shows no homology with known ion channel genes but contains two domains, composed of repeated structural units, known to mediate protein-protein interactions.A three dimensional in silico model of the two epitempin domains was built to predict the structure-function relationship and propose a functional model integrating previous experimental findings. Conserved and electrostatic charged regions of the model surface suggest a possible arrangement between the two domains and identifies a possible ADAM protein binding site in the β-propeller domain and another protein binding site in the leucine-rich repeat domain. The functional model indicates that epitempin could mediate the interaction between proteins localized to different synaptic sides in a static way, by forming a dimer, or in a dynamic way, by binding proteins at different times.The model was also used to predict effects of known disease-causing missense mutations. Most of the variants are predicted to alter protein folding while several other map to functional surface regions. In agreement with experimental evidence, this suggests that non-secreted LGI1 mutants could be retained within the cell by quality control mechanisms or by altering interactions required for the secretion process.

ADAM23, a Gene Related to LGI1, Is Not Linked to Autosomal Dominant Lateral Temporal Epilepsy

Autosomal dominant lateral temporal epilepsy (ADTLE) is an inherited epileptic syndrome characterized by ictal auditory symptoms or aphasia, negative MRI findings, and relatively benign evolution. Mutations responsible for ADLTE have been found in the LGI1 gene. The functions of the Lgi1 protein apparently are mediated by interactions with members of the ADAM protein family: it binds the postsynaptic receptor ADAM22 to regulate glutamate-AMPA currents at excitatory synapses and also the ADAM23 receptor to promote neurite outgrowth in vitro and dendritic arborization in vivo. Because alteration of each of these neuronal mechanisms may underlie ADLTE, ADAM22 and ADAM23 are candidate genes for this syndrome. In a previous work, we excluded a major role of ADAM22 in the aetiology of ADLTE. Here, we performed linkage analysis between microsatellite markers within or flanking the ADAM23 gene and ADLTE in 13 Italian families. The results exclude ADAM23 as major causative gene for ADLTE.

Episodic neurological channelopathies

Inherited episodic neurological disorders are often due to mutations in ion channels or their interacting proteins, termed channelopathies. There are a wide variety of such disorders, from those causing paralysis, to extreme pain, to ataxia. A common theme in these is alteration of action potential properties or synaptic transmission and a resulting increased propensity of the resulting tissue to enter into or stay in an altered excitability state. Manifestations of these disorders are triggered by an array of precipitants, all of which stress the particular affected tissue in some way and aid in propelling its activity into an aberrant state. Study of these disorders has aided in the understanding of disease risk factors and elucidated the cause of clinically related sporadic disorders. The findings from study of these disorders will aid in the diagnosis and efficient targeted treatment of affected patients.

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.

Epileptogenic ion channel mutations: from bedside to bench and, hopefully, back again

Mutations of genes coding for ion channels cause several genetically determined human epileptic syndromes. The identification of a gene variant linked to a particular disease gives important information, but it is usually necessary to perform functional studies in order to completely disclose the pathogenic mechanisms. The functional consequences of epileptogenic mutations have been studied both in vitro and in vivo with several experimental systems, studies that have provided significant knowledge on the pathogenic mechanisms that leads to inherited human epilepsies, and possibly also on the pathogenic mechanisms of non-genetic human epilepsies due to "acquired channelopathies". However, several open issues remain and difficulties in the interpretation of the experimental data have arisen that limit translational applications. We will highlight the value and the limits of different approaches to the study of epileptogenic channelopathies, focussing on the importance of the experimental systems in the assessment of the functional effects of the mutations and on the possible applications of the obtained results to the clinical practice.

Knockdown of zebrafish Lgi1a results in abnormal development, brain defects and a seizure-like behavioral phenotype

Epilepsy is a common disorder, typified by recurrent seizures with underlying neurological disorders or disease. Approximately one-third of patients are unresponsive to currently available therapies. Thus, a deeper understanding of the genetics and etiology of epilepsy is needed to advance the development of new therapies. Previously, treatment of zebrafish with epilepsy-inducing pharmacological agents was shown to result in a seizure-like phenotype, suggesting that fish provide a tractable model to understand the function of epilepsy-predisposing genes. Here, we report the first model of genetically linked epilepsy in zebrafish and provide an initial characterization of the behavioral and neurological phenotypes associated with morpholino (MO) knockdown of leucine-rich, glioma-inactivated 1a (lgi1a) expression. Mutations in the LGI1 gene in humans have been shown to predispose to a subtype of autosomal dominant epilepsy. Low-dose Lgi1a MO knockdown fish (morphants) appear morphologically normal but are sensitized to epilepsy-inducing drugs. High-dose Lgi1a morphants have morphological defects which persist into adult stages that are typified by smaller brains and eyes and abnormalities in tail shape, and display hyperactive swimming behaviors. Increased apoptosis was observed throughout the central nervous system of high-dose morphant fish, accounting for the size reduction of neural tissues. These observations demonstrate that zebrafish can be exploited to dissect the embryonic function(s) of genes known to predispose to seizure-like behavior in humans, and offer potential insight into the relationship between developmental neurobiological abnormalities and seizure.

Electroclinical characterization of epileptic seizures in leucine-rich, glioma-inactivated 1-deficient mice

Mutations of the LGI1 (leucine-rich, glioma-inactivated 1) gene underlie autosomal dominant lateral temporal lobe epilepsy, a focal idiopathic inherited epilepsy syndrome. The LGI1 gene encodes a protein secreted by neurons, one of the only non-ion channel genes implicated in idiopathic familial epilepsy. While mutations probably result in a loss of function, the role of LGI1 in the pathophysiology of epilepsy remains unclear. Here we generated a germline knockout mouse for LGI1 and examined spontaneous seizure characteristics, changes in threshold for induced seizures and hippocampal pathology. Frequent spontaneous seizures emerged in homozygous LGI1^−/− mice during the second postnatal week. Properties of these spontaneous events were examined in a simultaneous video and intracranial electroencephalographic recording. Their mean duration was 120 ± 12 s, and behavioural correlates consisted of an initial immobility, automatisms, sometimes followed by wild running and tonic and/or clonic movements. Electroencephalographic monitoring indicated that seizures originated earlier in the hippocampus than in the cortex. LGI1^−/− mice did not survive beyond postnatal day 20, probably due to seizures and failure to feed. While no major developmental abnormalities were observed, after recurrent seizures we detected neuronal loss, mossy fibre sprouting, astrocyte reactivity and granule cell dispersion in the hippocampus of LGI1^−/− mice. In contrast, heterozygous LGI1^+/− littermates displayed no spontaneous behavioural epileptic seizures, but auditory stimuli induced seizures at a lower threshold, reflecting the human pathology of sound-triggered seizures in some patients. We conclude that LGI1^+/− and LGI1^−/− mice may provide useful models for lateral temporal lobe epilepsy, and more generally idiopathic focal 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.

Is LGI2 the candidate gene for partial epilepsy with pericentral spikes?

Partial epilepsy with pericentral spikes (PEPS) is a familial epilepsy with disease locus mapped to human chromosome region 4p15; yet, the causative gene is unknown. In this work, arguments based on protein sequence analysis and patient-specific chromosomal deletions are provided for LGI2 as the prime candidate gene for PEPS among the 52 genes known at the genome locus 4p15. Furthermore, we suggest that two reports of patients that were not classified as PEPS but show very similar phenotypes and deletions in the PEPS disease locus, could in fact describe the same disease. To test this hypothesis, patients with diagnosed PEPS or the described similar phenotypes could be screened for mutations in LGI2 and other shortlisted candidate genes. The linkage between PEPS and its disease causing gene(s) would allow diagnosis of the disease based on genetic screening as well as hereditary studies. Furthermore, previous knowledge on molecular disease mechanisms of related LGI proteins, for example LGI1 and autosomal dominant lateral temporal epilepsy, could be applied to deepen the understanding of the PEPS disease mechanism at the molecular level, which may facilitate therapeutic intervention in the future. Supplementary Table is available at http://www.worldscinet.com/jbcb/.