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

Autosomal dominant lateral temporal epilepsy in a family exhibiting a rare heterozygous mutation and deletion in the leucine-rich glioma inactivated 1 gene

Autosomal dominant lateral temporal epilepsy (ADLTE) is an inherited syndrome caused by mutations in the leucine-rich glioma inactivated 1 (LGI1) gene. In a family with six ADLTE patients spanning four generations, our linkage and exome sequencing investigations revealed a rare frameshift heterozygous mutation in LGI1 (c.1494del(p.Phe498LeufsTer15)). Gene cloning methods were used to create plasmids with wild-type and mutant LGI1 alleles. Through transfection of HEK293 cells and primary neurons, they were utilized to assess the subcellular location of wild-type and mutant LGI1. Moreover, the plasmid-transfected primary neurons were analyzed for neuronal complexity and density of dendritic spines. According to our results. the mutation decreased LGI1 secretion in transfected HEK293 cells. In primary neurons, mutant LGI1 affected neuronal polarity and complexity. Our findings have broadened the phenotypic spectrum of LGI1 mutations and provided evidence regarding the pathogenicity of this mutation. In addition, we discovered new information about the role of LGI1 in the development of temporal lobe epilepsy, along with a possible link between neuronal polarity disorder and ADLTE.

Imaging Genetics in Epilepsy: Current Knowledge and New Perspectives

Epilepsy is a neurological network disease with genetics playing a much greater role than was previously appreciated. Unfortunately, the relationship between genetic basis and imaging phenotype is by no means simple. Imaging genetics integrates multidimensional datasets within a unified framework, providing a unique opportunity to pursue a global vision for epilepsy. This review delineates the current knowledge of underlying genetic mechanisms for brain networks in different epilepsy syndromes, particularly from a neural developmental perspective. Further, endophenotypes and their potential value are discussed. Finally, we highlight current challenges and provide perspectives for the future development of imaging genetics in epilepsy.

MICAL1 Monooxygenase in Autosomal Dominant Lateral Temporal Epilepsy: Role in Cytoskeletal Regulation and Relation to Cancer

Autosomal dominant lateral temporal epilepsy (ADLTE) is a genetic focal epilepsy associated with mutations in the LGI1, RELN, and MICAL1 genes. A previous study linking ADLTE with two MICAL1 mutations that resulted in the substitution of a highly conserved glycine residue for serine (G150S) or a frameshift mutation that swapped the last three C-terminal amino acids for 59 extra residues (A1065fs) concluded that the mutations increased enzymatic activity and promoted cell contraction. The roles of the Molecule Interacting with CasL 1 (MICAL1) protein in tightly regulated semaphorin signaling pathways suggest that activating MICAL1 mutations could result in defects in axonal guidance during neuronal development. Further studies would help to illuminate the causal relationships of these point mutations with ADLTE. In this review, we discuss the proposed pathogenesis caused by mutations in these three genes, with a particular emphasis on the G150S point mutation discovered in MICAL1. We also consider whether these types of activating MICAL1 mutations could be linked to cancer.

Expression Profile of miRs in Mesial Temporal Lobe Epilepsy: Systematic Review

Temporal lobe epilepsy (TLE) is one of the most common forms of focal epilepsy in children and adults. TLE is characterized by variable onset and seizures. Moreover, this form of epilepsy is often resistant to pharmacotherapy. The search for new mechanisms for the development of TLE may provide us with a key to the development of new diagnostic methods and a personalized approach to the treatment. In recent years, the role of non-coding ribonucleic acids (RNA) has been actively studied, among which microRNA (miR) is of the greatest interest. (1) Background: The purpose of the systematic review is to analyze the studies carried out on the role of miRs in the development of mesial TLE (mTLE) and update the existing knowledge about the biomarkers of this disease. (2) Methods: The search for publications was carried out in the databases PubMed, Springer, Web of Science, Clinicalkeys, Scopus, OxfordPress, Cochrane. The search was carried out using keywords and combinations. We analyzed publications for 2016–2021, including original studies in an animal model of TLE and with the participation of patients with TLE, thematic and systemic reviews, and Cochrane reviews. (3) Results: this thematic review showed that miR‒155, miR‒153, miR‒361‒5p, miR‒4668‒5p, miR‒8071, miR‒197‒5p, miR‒145, miR‒181, miR‒199a, miR‒1183, miR‒129‒2‒3p, miR‒143‒3p (upregulation), miR–134, miR‒0067835, and miR‒153 (downregulation) can be considered as biomarkers of mTLE. However, the roles of miR‒146a, miR‒142, miR‒106b, and miR‒223 are questionable and need further study. (4) Conclusion: In the future, it will be possible to consider previously studied miRs, which have high specificity and sensitivity in mTLE, as prognostic biomarkers (predictors) of the risk of developing this disease in patients with potentially epileptogenic structural damage to the mesial regions of the temporal lobe of the brain (congenital disorders of the neuronal migration and neurogenesis, brain injury, neuro-inflammation, tumor, impaired blood supply, neurodegeneration, etc.).

Semiology, EEG, and neuroimaging findings in temporal lobe epilepsies

Temporal lobe epilepsy (TLE) is the most common type of focal epilepsy. First descriptions of TLE date back in time and detailed portraits of epileptic seizures of temporal origin can be found in early medical reports as well as in the works of various artists and dramatists. Depending on the seizure onset zone, several subtypes of TLE have been identified, each one associated with peculiar ictal semiology. TLE can result from multiple etiological causes, ranging from genetic to lesional ones. While the diagnosis of TLE relies on detailed analysis of clinical as well as electroencephalographic (EEG) features, the lesions responsible for seizure generation can be highlighted by multiple brain imaging modalities or, in selected cases, by genetic investigations. TLE is the most common cause of refractory epilepsy and despite the great advances in diagnostic tools, no lesion is found in around one-third of patients. Surgical treatment is a safe and effective option, requiring presurgical investigations to accurately identify the seizure onset zone (SOZ). In selected cases, presurgical investigations need intracerebral investigations (such as stereoelectroencephalography) or dedicated metabolic imaging techniques (interictal PET and ictal SPECT) to correctly identify the brain structures to be removed.

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

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

Epilepsy with auditory features: Contribution of known genes in 112 patients

Epilepsy with Auditory Features (EAF) is a focal epilepsy syndrome mainly of unknown aetiology. LGI1 and RELN have been identified as the main cause of Autosomal Dominant EAF and anecdotally reported in non-familial cases. Pathogenic variants in SCN1A and DEPDC5 have also been described in a few EAF probands belonging to families with heterogeneous phenotypes and incomplete penetrance. We aimed to estimate the contribution of these genes to the disorder by evaluating the largest cohort of EAF. We included 112 unrelated EAF cases (male/female: 52/60) who underwent genetic analysis by next-generation sequencing (NGS) techniques. Thirty-three (29.5%) were familial cases. We identified a genetic diagnosis for 8% of our cohort, including pathogenic/likely pathogenic variants (4/8 novel) in LGI1 (2.7%, CI: 0.6-7.6); RELN (1.8%; CI: 0.2-6.3); SCN1A (2.7%; CI: 0.6-7.6) and DEPDC5 (0.9%; CI 0-4.9).This study shows that the contribution of each of the known genes to the overall disorder is limited and that the genetic background of EAF is still largely unknown. Our data emphasize the genetic heterogeneity of EAF and will inform the diagnosis and management of individuals with this disorder.

The clinical characters and gene detection in a familial temporal lobe epilepsy with auditory aura

Auditory aura was the very important clinical character in familial temporal Lobe epilepsy. LGI1 was the main pathogenic gene. The inheritance mode of this disease was autosomal dominant. We describes the clinical characters and gene detection in 7 patients in a temporal lobe epilepsy family with auditory aura. All patients in this family were diagnosed as temporal lobe epilepsy and had the same mutation: the splice site mutation in No. 2 base of the intron after the first exon in gene LGI1, c.215+2T>A, which induced the abnormal expression of peptide protein after the No. 71 amino acid encoded by LGI1. Some of the antiepileptic drugs, such as carbamazepine, oxcarbazepine, could be effective.

Advances in genetic testing and optimization of clinical management in children and adults with epilepsy

Introduction: Epileptic disorders are a heterogeneous group of medical conditions with epilepsy as the common denominator. Genetic causes, electro-clinical features, and management significantly vary according to the specific condition.Areas covered: Relevant diagnostic advances have been achieved thanks to the advent of Next Generation Sequencing (NGS)-based molecular techniques. These revolutionary tools allow to sequence all coding (whole exome sequencing, WES) and non-coding (whole genome sequencing, WGS) regions of human genome, with a potentially huge impact on patient care and scientific research.Expert opinion: The application of these tests in children and adults with epilepsy has led to the identification of new causative genes, widening the knowledge on the pathophysiology of epilepsy and resulting in therapeutic implications. This review will explore the most recent advancements in genetic testing and provide up-to-date approaches for the choice of the correct test in patients with epilepsy.

Mutations in MICAL-1cause autosomal-dominant lateral temporal epilepsy

OBJECTIVE

Autosomal-dominant lateral temporal epilepsy (ADLTE) is a genetic focal epilepsy characterized by auditory symptoms. Two genes, LGI1 and RELN, encoding secreted proteins, are implicated in the etiology of ADLTE, but half of the affected families remain genetically unsolved, and the underlying molecular mechanisms are yet to be clarified. We aimed to identify additional genes causing ADLTE to better understand the genetic basis and molecular pathway underlying this epileptic disorder.

METHODS

A cohort of Italian ADLTE families was examined by whole exome sequencing combined with genome-wide single-nucleotide polymorphism-array linkage analysis.

RESULTS

We identified two ADLTE-causing variants in the MICAL-1 gene: a p.Gly150Ser substitution occurring in the enzymatically active monooxygenase (MO) domain and a p.Ala1065fs frameshift indel in the C-terminal domain, which inhibits the oxidoreductase activity of the MO domain. Each variant segregated with ADLTE in a single family. Examination of candidate variants in additional genes excluded their implication in ADLTE. In cell-based assays, both variants significantly increased MICAL-1 oxidoreductase activity and induced cell contraction in COS7 cells, which likely resulted from deregulation of F-actin dynamics.

INTERPRETATION

MICAL-1 oxidoreductase activity induces disassembly of actin filaments, thereby regulating the organization of the actin cytoskeleton in developing and adult neurons and in other cell types. This suggests that dysregulation of the actin cytoskeleton dynamics is a likely mechanism by which MICAL-1 pathogenic variants lead to ADLTE. Ann Neurol 2018;83:483-493.

CNTNAP2 mutations and autosomal dominant epilepsy with auditory features

Autosomal dominant epilepsy with auditory features (ADEAF) is clinically characterized by focal seizures with prominent auditory or aphasic auras and absence of structural brain abnormalities. Mutations in LGI1 and RELN genes account for the disorder in about 50% of ADEAF families. In a recent paper, a heterozygous intragenic deletion in the CNTNAP2 gene has been associated to ADEAF in a single family. We screened 28 ADEAF families for mutations in CNTNAP2 by next generation sequencing and copy number variation analyses and found no likely pathogenic mutations segregating with the disease. CNTNAP2 should be screened in genetically unsolved ADEAF families, but causative mutations are expected to be infrequent in this gene.

The clinical phenotype of autosomal dominant lateral temporal lobe epilepsy related to reelin mutations

OBJECTIVE

To describe the clinical phenotype of 7 families with Autosomal Dominant Lateral Temporal Lobe Epilepsy (ADLTE) related to Reelin (RELN) mutations comparing the data with those observed in 12 LGI1-mutated pedigrees belonging to our series.

METHODS

Out of 40 Italian families with ADLTE, collected by epileptologists participating in a collaborative study of the Commission for Genetics of the Italian League against Epilepsy encompassing a 14-year period (2000-2014), 7 (17.5%) were found to harbor heterozygous RELN mutations. The whole series also included 12 (30%) LGI1 mutated families and 21 (52.5%) non-mutated pedigrees. The clinical, neurophysiological, and neuroradiological findings of RELN and LGI1 mutated families were analyzed.

RESULTS

Out of 28 affected individuals belonging to 7 RELN mutated families, 24 had sufficient clinical data available for the study. In these patients, the epilepsy onset occurred at a mean age of 20years, with focal seizures characterized by auditory auras in about 71% of the cases, associated in one-third of patients with aphasia, visual disturbances or other less common symptoms (vertigo or déjà-vu). Tonic-clonic seizures were reported by almost all patients (88%), preceded by typical aura in 67% of cases. Seizures were precipitated by environmental noises in 8% of patients and were completely or almost completely controlled by antiepileptic treatment in the vast majority of cases (96%). The interictal EEG recordings showed epileptiform abnormalities or focal slow waves in 80% of patients, localized over the temporal regions, with marked left predominance and conventional 1,5T MRI scans were not contributory. By comparing these findings with those observed in families with LGI1 mutations, we did not observe significant differences except for a higher rate of left-sided EEG abnormalities in the RELN group.

SIGNIFICANCE

Heterozygous RELN mutations cause a typical ADLTE syndrome, indistinguishable from that associated with LGI1 mutations.

Secretion-Positive LGI1 Mutations Linked to Lateral Temporal Epilepsy Impair Binding to ADAM22 and ADAM23 Receptors

Autosomal dominant lateral temporal epilepsy (ADTLE) is a focal epilepsy syndrome caused by mutations in the LGI1 gene, which encodes a secreted protein. Most ADLTE-causing mutations inhibit LGI1 protein secretion, and only a few secretion-positive missense mutations have been reported. Here we describe the effects of four disease-causing nonsynonymous LGI1 mutations, T380A, R407C, S473L, and R474Q, on protein secretion and extracellular interactions. Expression of LGI1 mutant proteins in cultured cells shows that these mutations do not inhibit protein secretion. This finding likely results from the lack of effects of these mutations on LGI1 protein folding, as suggested by 3D protein modelling. In addition, immunofluorescence and co-immunoprecipitation experiments reveal that all four mutations significantly impair interaction of LGI1 with the ADAM22 and ADAM23 receptors on the cell surface. These results support the existence of a second mechanism, alternative to inhibition of protein secretion, by which ADLTE-causing LGI1 mutations exert their loss-of-function effect extracellularly, and suggest that interactions of LGI1 with both ADAM22 and ADAM23 play an important role in the molecular mechanisms leading to ADLTE.

Temporal lobe epilepsy is the most common form of focal epilepsy. It is frequently associated with structural brain abnormalities, but genetic forms caused by mutations in major genes have also been described. Autosomal dominant lateral temporal epilepsy (ADLTE) is a familial condition characterized by focal seizures with prominent auditory symptoms. ADLTE-causing mutations are found in the LGI1 gene in about 30% of affected families. LGI1 encodes a protein, LGI1, that is secreted by neurons. Most LGI1 mutations suppress protein secretion, thereby preventing protein function in the extracellular environment. In this paper, we examine the effects of four LGI1 mutations and show that they do not inhibit secretion of the LGI1 protein but impair its interaction with the neuronal receptors ADAM22 and ADAM23. In agreement with these findings, a three- dimensional model of the protein predicts that these mutations have no impact on LGI1 structure but instead may affect amino acids that are critical for interactions with ADAM receptors. Our results provide novel evidence for an extracellular mechanism through which mutant LGI1 proteins cause ADLTE and strengthen the importance of LGI1-ADAM22/23 protein complex in the mechanisms underlying ADLTE.

Seizures and Epilepsies due to Channelopathies and Neurotransmitter Receptor Dysfunction: A Parallel between Genetic and Immune Aspects

Despite intensive research activity leading to many important discoveries, the pathophysiological mechanisms underlying seizures and epilepsy remain poorly understood. An important number of specific gene defects have been related to various forms of epilepsies, and autoimmunity and epilepsy have been associated for a long time. Certain central nervous system proteins have been involved in epilepsy or acute neurological diseases with seizures either due to underlying gene defects or immune dysfunction. Here, we focus on 2 of them that have been the object of particular attention and in-depth research over the past years: the N-methyl-D-aspartate receptor and the leucin-rich glioma-inactivated protein 1 (LGI1). We also describe illustrative examples of situations in which genetics and immunology meet in the complex pathways that underlie seizures and epilepsy.

Joan of Arc: Sanctity, witchcraft or epilepsy?

OBJECTIVE

The objective of this article is to describe whether Joan of Arc had epilepsy and how that may have influenced her sense of mission and ability to encourage thousands of people to help her to chase the English out of France.

METHODS

Documentation of her Trial of Condemnation in 1431 provides a description of her episodes of experienced voices and visions.

RESULTS

From the age of thirteen, Joan of Arc experienced frequent episodes of auditory hallucinations associated with elementary or complex visual hallucinations (e.g., a great light or human faces). These had sudden onset, lasting seconds or minutes at most, and occurred when awake or during sleep, arousing her. Some could be triggered by an auditory stimulus. She had no disorganized thought between the episodes.

CONCLUSIONS

The semiology of the episodes is very suggestive of epileptic seizures, which have been considered as ecstatic by some authors or as partial epilepsy with auditory features by others, which seems more concordant with the ictal symptoms. The auditory and visual hallucinations could have had a religious content because during her childhood and adolescence, she was brought up in a religious environment, insomuch as this content first undefined only appeared after a few seizures. We can suppose that such hallucinations, without the knowledge of their medical origin, gave her a sense of divine mission, hence, a real strength to try to accomplish the orders she heard during the episodes. Her role during the Hundred Years' War and her narration of her strange episodes led her to be burned for heresy at the age of nineteen, yet rehabilitated 25 years later and to be canonized for her achievements in 1920. This article is part of a Special Issue entitled "Epilepsy, Art, and Creativity".

DEPDC5 mutations are not a frequent cause of familial temporal lobe epilepsy

Mutations in the DEPDC5 (DEP domain-containing protein 5) gene are a major cause of familial focal epilepsy with variable foci (FFEVF) and are predicted to account for 12-37% of families with inherited focal epilepsies. To assess the clinical impact of DEPDC5 mutations in familial temporal lobe epilepsy, we screened a collection of Italian families with either autosomal dominant lateral temporal epilepsy (ADLTE) or familial mesial temporal lobe epilepsy (FMTLE). The probands of 28 families classified as ADLTE and 17 families as FMTLE were screened for DEPDC5 mutations by whole exome or targeted massive parallel sequencing. Putative mutations were validated by Sanger sequencing. We identified a DEPDC5 nonsense mutation (c.918C>G; p.Tyr306*) in a family with two affected members, clinically classified as FMTLE. The proband had temporal lobe seizures with prominent psychic symptoms (déjà vu, derealization, and forced thoughts); her mother had temporal lobe seizures, mainly featuring visceral epigastric auras and anxiety. In total, we found a single DEPDC5 mutation in one of (2.2%) 45 families with genetic temporal lobe epilepsy, a proportion much lower than that reported in other inherited focal epilepsies.

Heterozygous reelin mutations cause autosomal-dominant lateral temporal epilepsy

Autosomal-dominant lateral temporal epilepsy (ADLTE) is a genetic epilepsy syndrome clinically characterized by focal seizures with prominent auditory symptoms. ADLTE is genetically heterogeneous, and mutations in LGI1 account for fewer than 50% of affected families. Here, we report the identification of causal mutations in reelin (RELN) in seven ADLTE-affected families without LGI1 mutations. We initially investigated 13 ADLTE-affected families by performing SNP-array linkage analysis and whole-exome sequencing and identified three heterozygous missense mutations co-segregating with the syndrome. Subsequent analysis of 15 small ADLTE-affected families revealed four additional missense mutations. 3D modeling predicted that all mutations have structural effects on protein-domain folding. Overall, RELN mutations occurred in 7/40 (17.5%) ADLTE-affected families. RELN encodes a secreted protein, Reelin, which has important functions in both the developing and adult brain and is also found in the blood serum. We show that ADLTE-related mutations significantly decrease serum levels of Reelin, suggesting an inhibitory effect of mutations on protein secretion. We also show that Reelin and LGI1 co-localize in a subset of rat brain neurons, supporting an involvement of both proteins in a common molecular pathway underlying ADLTE. Homozygous RELN mutations are known to cause lissencephaly with cerebellar hypoplasia. Our findings extend the spectrum of neurological disorders associated with RELN mutations and establish a link between RELN and LGI1, which play key regulatory roles in both the developing and adult brain.

Epilepsy with auditory features: A heterogeneous clinico-molecular disease

Objective:

To identify novel genes implicated in epilepsy with auditory features (EAF) in phenotypically heterogeneous families with unknown molecular basis.

Methods:

We identified 15 probands with EAF in whom an LGI1 mutation had been excluded. We performed electroclinical phenotyping on all probands and available affected relatives. We used whole-exome sequencing (WES) in 20 individuals with EAF (including all the probands and 5 relatives) to identify single nucleotide variants, small insertions/deletions, and copy number variants.

Results:

WES revealed likely pathogenic variants in genes that had not been previously associated with EAF: a CNTNAP2 intragenic deletion, 2 truncating mutations of DEPDC5, and a missense SCN1A change.

Conclusions:

EAF is a clinically and molecularly heterogeneous disease. The association of EAF with CNTNAP2, DEPDC5, and SCN1A mutations widens the phenotypic spectrum related to these genes. CNTNAP2 encodes CASPR2, a member of the voltage-gated potassium channel complex in which LGI1 plays a role. The finding of a CNTNAP2 deletion emphasizes the importance of this complex in EAF and shows biological convergence.

Autosomal dominant lateral temporal epilepsy (ADLTE): novel structural and single-nucleotide LGI1 mutations in families with predominant visual auras

PURPOSE

Autosomal dominant lateral temporal epilepsy (ADLTE) is a genetic focal epilepsy syndrome characterized by prominent auditory or aphasic symptoms. Mutations in LGI1 account for less than 50% of ADLTE families. We assessed the impact of LGI1 microrearrangements in a collection of ADLTE families and sporadic lateral temporal epilepsy (LTE) patients, and investigated novel ADLTE and LTE patients.

METHODS

Twenty-four ADLTE families and 140 sporadic LTE patients with no evidence of point mutations in LGI1 were screened for copy number alterations using multiplex ligation-dependent probe amplification (MLPA). Newly ascertained familial and sporadic LTE patients were clinically investigated, and interictal EEG and MRI findings were obtained; probands were tested for LGI1 mutations by direct exon sequencing or denaturing high performance liquid chromatography.

RESULTS

We identified a novel microdeletion spanning LGI1 exon 2 in a family with two affected members, both presenting focal seizures with visual symptoms. Also, we identified a novel LGI1 missense mutation (c.1118T > C; p.L373S) in a newly ascertained family with focal seizures with prominent visual auras, and another missense mutation (c.856T > C; p.C286R) in a sporadic patient with auditory seizures.

CONCLUSIONS

We describe two novel ADLTE families with predominant visual auras segregating pathogenic LGI1 mutations. These findings support the notion that, in addition to auditory symptoms, other types of auras can be found in patients carrying LGI1 mutations. The identification of a novel microdeletion in LGI1, the second so far identified, suggests that LGI1 microrearrangements may not be exceptional.

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.

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.

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.

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.