Four new families with autosomal dominant partial epilepsy with auditory features: clinical description and linkage to chromosome 10q24

Consanguinity in patients with mesial temporal lobe epilepsy due to hippocampal sclerosis in a Saudi population

Objectives:

To investigate if there is an association between consanguinity and hippocampal sclerosis (HS) in the Saudi population.

Methods:

A retrospective case-control study was conducted by assessing the prevalence of consanguinity in patients with pathologically proven HS, who underwent epilepsy surgery at King Faisal Specialist Hospital and Research Center, Jeddah, Saudi Arabia, between January 2004 and December 2015. We reviewed the medical records to extract data, which included; age, gender, duration of epilepsy, history of febrile seizure, family history of epilepsy in a first or second-degree relative, and pathology reports.

Results:

A total of 120 patients, out of which 40 patients (65% male) having mesial temporal lobe epilepsy due to HS, and 80 controls (56% male) with cryptogenic epilepsy, were identified. Twenty-two patients (53.5%) in the HS group had a history of consanguinity. In the control group, 30 patients (37.5%) had a history of consanguinity. The odds ratio was 2.04 (95% confidence interval = 0.94 - 4.4, p = 0.052). A family history of epilepsy was found in 28% of the patients with HS and 32.5% cryptogenic epilepsy. Only 8 patients (19.5%) with HS reported a history of febrile seizure.

Conclusion:

Our retrospective case-control study suggests that consanguinity might increase the likelihood of developing HS.

Genetic and epigenetic mechanisms of epilepsy: a review

Epilepsy is a common episodic neurological disorder or condition characterized by recurrent epileptic seizures, and genetics seems to play a key role in its etiology. Early linkage studies have localized multiple loci that may harbor susceptibility genes to epilepsy, and mutational analyses have detected a number of mutations involved in both ion channel and nonion channel genes in patients with idiopathic epilepsy. Genome-wide studies of epilepsy have found copy number variants at 2q24.2-q24.3, 7q11.22, 15q11.2-q13.3, and 16p13.11-p13.2, some of which disrupt multiple genes, such as NRXN1, AUTS2, NLGN1, CNTNAP2, GRIN2A, PRRT2, NIPA2, and BMP5, implicated for neurodevelopmental disorders, including intellectual disability and autism. Unfortunately, only a few common genetic variants have been associated with epilepsy. Recent exome-sequencing studies have found some genetic mutations, most of which are located in nonion channel genes such as the LGI1, PRRT2, EFHC1, PRICKLE, RBFOX1, and DEPDC5 and in probands with rare forms of familial epilepsy, and some of these genes are involved with the neurodevelopment. Since epigenetics plays a role in neuronal function from embryogenesis and early brain development to tissue-specific gene expression, epigenetic regulation may contribute to the genetic mechanism of neurodevelopment through which a gene and the environment interacting with each other affect the development of epilepsy. This review focused on the analytic tools used to identify epilepsy and then provided a summary of recent linkage and association findings, indicating the existence of novel genes on several chromosomes for further understanding of the biology of epilepsy.

Glutamatergic neuron-targeted loss of LGI1 epilepsy gene results in seizures

Leucin-rich, glioma inactivated 1 (LGI1) is a secreted protein linked to human seizures of both genetic and autoimmune aetiology. Mutations in the LGI1 gene are responsible for autosomal dominant temporal lobe epilepsy with auditory features, whereas LGI1 autoantibodies are involved in limbic encephalitis, an acquired epileptic disorder associated with cognitive impairment. We and others previously reported that Lgi1-deficient mice have early-onset spontaneous seizures leading to premature death at 2-3 weeks of age. Yet, where and when Lgi1 deficiency causes epilepsy remains unknown. To address these questions, we generated Lgi1 conditional knockout (cKO) mice using a set of universal Cre-driver mouse lines. Selective deletion of Lgi1 was achieved in glutamatergic pyramidal neurons during embryonic (Emx1-Lgi1cKO) or late postnatal (CaMKIIα-Lgi1cKO) developmental stages, or in gamma amino butyric acidergic (GABAergic) parvalbumin interneurons (PV-Lgi1cKO). Emx1-Lgi1cKO mice displayed early-onset and lethal seizures, whereas CaMKIIα-Lgi1cKO mice presented late-onset occasional seizures associated with variable reduced lifespan. In contrast, neither spontaneous seizures nor increased seizure susceptibility to convulsant were observed when Lgi1 was deleted in parvalbumin interneurons. Together, these data showed that LGI1 depletion restricted to pyramidal cells is sufficient to generate seizures, whereas seizure thresholds were unchanged after depletion in gamma amino butyric acidergic parvalbumin interneurons. We suggest that LGI1 secreted from excitatory neurons, but not parvalbumin inhibitory neurons, makes a major contribution to the pathogenesis of LGI1-related epilepsies. Our data further indicate that LGI1 is required from embryogenesis to adulthood to achieve proper circuit functioning.

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.

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.

Hyperactive behavior in a family with autosomal dominant lateral temporal lobe epilepsy caused by a mutation in the LGI1/epitempin gene

Autosomal dominant lateral temporal lobe epilepsy (ADLTE) is characterized by focal seizures with auditory features or aphasia. Mutations in the leucine-rich glioma-inactivated 1 (LGI1) gene have been reported in up to 50% of families with ADLTE. Attention-deficit/hyperactivity disorder (ADHD) symptoms have not yet been reported in these families. Clinical data were collected from a family with five affected members. Leucine-rich glioma-inactivated 1 exons and boundaries were sequenced by standard methods. Attention-deficit/hyperactivity disorder symptoms were scored based on the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) criteria. Affected members had seizures with auditory features and psychic auras, and some experienced nightmares. A heterozygous c.431+1G>A substitution in LGI1 was detected in all members. Significantly more hyperactivity symptoms were found in family members carrying the LGI1 mutation. This study expands the phenotypic spectrum associated with ADLTE due to LGI1 mutation and underlines the need for more systematic evaluation of ADHD and related symptoms.

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.

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.

Differential brain glucose metabolic patterns in antipsychotic-naïve first-episode schizophrenia with and without auditory verbal hallucinations

BACKGROUND

Auditory verbal hallucinations (AVHs) are a core symptom of schizophrenia. Previous reports on neural activity patterns associated with AVHs are inconsistent, arguably owing to the lack of an adequate control group (i.e., patients with similar characteristics but without AVHs) and neglect of the potential confounding effects of medication.

METHODS

The current study was conducted in a homogeneous group of patients with schizophrenia to assess whether the presence or absence of AVHs was associated with differential regional cerebral glucose metabolic patterns. We investigated differences between patients with commenting AVHs and patients without AVHs among a group of dextral antipsychotic-naive inpatients with acute first-episode schizophrenia examined with [(18)F]fluoro-deoxyglucose positron emission tomography (FDG-PET) at rest. Univariate and multivariate approaches were used to establish between-group differences.

RESULTS

We included 9 patients with AVHs and 7 patients without AVHs in this study. Patients experiencing AVHs during FDG uptake had significantly higher metabolic rates in the left superior and middle temporal cortices, bilateral superior medial frontal cortex and left caudate nucleus (cluster level p < 0.005, family wise error-corrected, and bootstrap ratio > 3.3, respectively). Additionally, the multivariate method identified hippocampal-parahippocampal, cerebellar and parietal relative hypoactivity during AVHs in both hemispheres (bootstrap ratio < -3.3).

LIMITATIONS

The FDG-PET imaging technique does not provide information regarding the temporal course of neural activity. The limited sample size may have increased the risk of false-negative findings.

CONCLUSION

Our results indicate that AVHs in patients with schizophrenia may be mediated by an alteration of neural pathways responsible for normal language function. Our findings also point to the potential role of the dominant caudate nucleus and the parahippocampal gyri in the pathophysiology of AVHs. We discuss the relevance of phenomenology-based grouping in the study of AVHs.

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.

Evaluation of depression risk in LGI1 mutation carriers

PURPOSE

Depression is the most common comorbid condition in epilepsy. The cause of this comorbidity is unknown, and could involve psychosocial consequences of epilepsy, treatment side effects, seizure manifestations, or common neurobiologic mechanisms. One hypothesis of particular interest is a shared genetic susceptibility to epilepsy and depression. We tested this hypothesis by studying depressive symptoms in families with an identified genetic form of epilepsy: autosomal dominant partial epilepsy with auditory features caused by mutations in the leucine-rich, glioma inactivated 1 gene (LGI1).

METHODS

A standardized depression screen was administered to 94 individuals from 11 families with mutations in LGI1, including 38 mutation carriers with epilepsy (AC), 11 clinically unaffected mutation carriers (UC), and 45 noncarriers (NC).

RESULTS

Current depressive symptom scores were significantly higher in AC than in NC, an association that remained after excluding depressive symptoms that appeared likely to be caused by antiepileptic medication use. However, scores did not differ between UC and NC.

DISCUSSION

Although LGI1 mutation carriers who were clinically affected with epilepsy had increased depressive symptoms, mutation carriers without epilepsy did not. These findings suggest that the increase in depressive symptoms in affected individuals from these families is related to epilepsy or its treatment rather than to LGI1 mutations per se.

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.

LGI1 mutations in autosomal dominant and sporadic lateral temporal epilepsy

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

Altered language processing in autosomal dominant partial epilepsy with auditory features

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Analysis of LGI1 promoter sequence, PDYN and GABBR1 polymorphisms in sporadic and familial lateral temporal lobe epilepsy

Autosomal dominant lateral temporal epilepsy (ADTLE) is a genetically transmitted epileptic syndrome characterized by focal seizures with predominant auditory symptoms likely originating from the lateral region of the temporal lobe. Mutations in coding region or exon splice sites of the leucine-rich, glioma-inactivated 1 (LGI1) gene account for about 50% of ADLTE families. De novo LGI1 mutations of the same kind have also been found in about 2.5% of non-familial cases with idiopathic partial epilepsy with auditory features (IPEAF). In both conditions, mutations in the LGI1 promoter region have not been reported. We sequenced the minimal promoter region of LGI1 in the probands of 16 ADLTE families and in 104 sporadic IPEAF patients and no mutations clearly linked to the disease were found. However, two polymorphisms, -500G>A and -507G>A, with potential functional implications were identified and analysed in the cohort of sporadic IPEAF patients but their frequencies did not differ from those found in a control population of similar age, gender and geographic origin. We also analysed in our study population the GABA(B) receptor 1 c.1465G>A and the prodynorphin promoter 68-bp repeat polymorphisms, previously associated with temporal lobe epilepsy. None of these polymorphisms showed a significant association with IPEAF, whereas a tendency towards association with the prodynorphin low expression (L) alleles was found in the small group of ADLTE index cases, in agreement with previous studies suggesting that this polymorphism is a susceptibility factor in familial forms of temporal lobe epilepsy.

Autosomal dominant lateral temporal epilepsy: absence of mutations in ADAM22 and Kv1 channel genes encoding LGI1-associated proteins

Mutations in the LGI1 gene are linked to autosomal dominant lateral temporal epilepsy (ADTLE) in about half of the families tested, suggesting that ADLTE is genetically heterogeneous. Recently, the Lgi1 protein has been found associated with different protein complexes and two distinct molecular mechanisms possibly underlying ADLTE have been hypothesized: the one recognizes Lgi1 as a novel subunit of the presynaptic Kv1 potassium channel implicated in the regulation of channel inactivation, the other suggests that Lgi1 acts as a ligand that selectively binds to the postsynaptic receptor ADAM22, thereby regulating the glutamate-AMPA neurotransmission. Both mechanisms imply that LGI1 mutations result in alteration of synaptic currents, though of different types. Since their protein products have been found associated with Lgi1, the Kv1 channel subunit genes KCNA1, KCNA4, and KCNAB1 and ADAM22 can be considered strong candidates for ADLTE. We sequenced their coding exons and flanking splice sites in the probands of 9 carefully ascertained ADLTE families negative for LGI1 mutations. We failed to detect any mutation segregating with the disease, but identified several previously unreported polymorphisms. An association study of four non-synonymous variants (three found in ADAM22, one in KCNA4) in a population of 104 non-familial lateral temporal epilepsy cases did not show any modification of susceptibility to this disorder. Altogether, our results suggest that neither ADAM22 nor any of the three Kv1 channel genes are major causative genes for ADLTE.

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

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

A method for estimating penetrance from families sampled for linkage analysis

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

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

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

Speech-induced Aphasic Seizures in Epilepsy Caused by LGI1 Mutation

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

LGI1: a gene involved in epileptogenesis and glioma progression?

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

LGI1 gene mutation screening in sporadic partial epilepsy with auditory features

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

Recruitment of families for genetic studies of epilepsy

PURPOSE

Study of families containing multiple affected individuals is essential for genetic research on the epilepsies, yet practically nothing has been published about methods for identification and recruitment of families or expected participation rates. Here we describe the strategy used for data collection in a genetic linkage study, to provide guidelines for efficient design of new studies.

METHODS

Potentially eligible families were ascertained from private physicians, clinics, and self-referrals. Participation rates were examined at each step of the recruitment process, according to ascertainment source, initial contact method, gender, and ethnicity.

RESULTS

Among 320 potentially eligible families identified, only 68 (21%) were successfully enrolled. Contact was established with an index subject in 83% of families, and a screen for eligibility was completed in 88% of these. However, only 54% of screened families were confirmed to be eligible, and of these, only 54% were enrolled. In eligible families, 79% of index subjects agreed to participate; the low family enrollment rates resulted largely from refusals by other family members whose participation was needed for linkage analysis. At each step in the recruitment process, the participation rate was higher in self-referred than in other families.

CONCLUSIONS

Recruitment of families for genetic studies is labor-intensive; many potentially eligible families may have to be screened for each family enrolled. Recruitment is easier with self-referred families than with those identified through other methods. The introduction of standardized methods for identification of eligible families from clinical settings can improve efficiency.

Clinical and genetic aspects of idiopathic epilepsies in childhood

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

Structural abnormalities are similar in familial and nonfamilial mesial temporal lobe epilepsy

BACKGROUND/OBJECTIVE

Diffuse temporal lobe abnormalities can be observed on MRI of patients with mesial temporal lobe epilepsy (MTLE). Our objective was to perform qualitative and quantitative analyses of temporal lobe structures in patients with familial MTLE (FMTLE) and nonfamilial MTLE.

METHODS

Two groups of patients were ascertained: 67 FMTLE patients (14 with refractory seizures) and 30 patients with nonfamilial refractory MTLE. We performed qualitative analyses of MRI (with multiplanar reconstruction) and volumes of hippocampi and anterior temporal lobes in all patients, and in a normal control group of 23 individuals. We used the Chi-square test and ANOVA for statistical analyses.

RESULTS

We identified anterior temporal lobe abnormalities by visual analysis in only 4% of FMTLE patients and atrophy of the anterior temporal lobe by volumetric analysis in 19%. In the group of nonfamilial MTLE patients we found anterior temporal lobe abnormalities by visual analysis in 17% of patients and anterior temporal lobe atrophy in 13%. Hippocampal atrophy was present in 90% of FMTLE and in 83% of nonfamilial MTLE. No signs of cortical dysplasia were observed.

CONCLUSION

Anterior temporal lobe atrophy and other abnormalities outside the mesial portion of temporal lobes were infrequent in both familial and nonfamilial MTLE patients. Despite the genetic basis, hippocampal atrophy in FMTLE is not associated with other abnormalities outside the mesial temporal regions.

LGI1 mutations in autosomal dominant partial epilepsy with auditory features

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Monogenic idiopathic epilepsies

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

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Familial partial epilepsy with variable foci in a Dutch family: clinical characteristics and confirmation of linkage to chromosome 22q

PURPOSE

Three forms of idiopathic partial epilepsy with autosomal dominant inheritance have been described: (a) autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE); (b) autosomal dominant lateral temporal epilepsy (ADLTE) or partial epilepsy with auditory features (ADPEAF); and (c) familial partial epilepsy with variable foci (FPEVF). Here we describe linkage analysis in a Dutch four-generation family with epilepsy fulfilling criteria of both ADNFLE and FPEVF.

METHODS

Clinical characteristics and results of EEG, computed tomography (CT), and magnetic resonance imaging (MRI) were evaluated in a family with autosomal dominantly inherited partial epilepsy with apparent incomplete penetrance. Linkage analysis was performed with markers of the ADNFLE (1p21, 15q24, 20q13.3) and FPEVF (2q, 22q11-q12) loci.

RESULTS

Epilepsy was diagnosed in 10 relatives. Age at onset ranged from 3 months to 24 years. Seizures were mostly tonic, tonic-clonic, or hyperkinetic, with a wide variety in symptoms and severity. Most interictal EEGs showed no abnormalities, but some showed frontal, central, and/or temporal spikes and spike-wave complexes. From two patients, an ictal EEG was available, showing frontotemporal abnormalities in one and frontal and central abnormalities in the other. Linkage analysis with the known loci for ADNFLE and FPEVF revealed linkage to chromosome 22q in this family.

CONCLUSIONS

The clinical characteristics of this family fulfilled criteria of both ADNFLE and FPEVF. The frequent occurrence of seizures during daytime and the observation of interictal EEG abnormalities originating from different cortical areas were more in agreement with FPEVF. The observed linkage to chromosome 22q supported the diagnosis of FPEVF and confirmed that this locus is responsible for this syndrome.

Autosomal dominant lateral temporal epilepsy: clinical spectrum, new epitempin mutations, and genetic heterogeneity in seven European families

PURPOSE

[corrected] To describe the clinical and genetic findings of seven additional pedigrees with autosomal dominant lateral temporal epilepsy (ADLTE).

METHODS

A personal and family history was obtained from each affected and unaffected member, along with a physical and neurologic examination. Routine and sleep EEGs, computed tomography (CT), or magnetic resonance imaging (MRI) were performed in almost all the patients. DNAs from family members were typed with several microsatellite markers localized on either side of LGI1 at 10q24 and screened for LGI1 mutations.

RESULTS

The seven families included a total of 34 affected individuals (10 deceased). The age at onset ranged between 8 and 50 years (average, 22 years). Twenty-six patients had clear-cut focal (elementary, complex, or secondarily generalized) seizures, characterized by prominent auditory auras in 68% of the cases. Less frequent ictal symptoms were visual, psychic, or aphasic seizures, the latter occurring in isolation in one family. The attacks were rare and well controlled by antiepileptic drug treatment but recurred after drug discontinuation. Interictal EEGs were usually unrevealing. MRI or CT scans were negative. Analysis of LGI1/Epitempin exons failed to show mutations in three pedigrees. Linkage analysis strongly suggested exclusion of linkage in one of these families. We found two novel missense mutations, a T-->C substitution in exon 6 at position 598, and a T-->A transition in exon 8 at position 1295, the latter being detected in a family with aphasic seizures.

CONCLUSIONS

Our data confirm the inclusion of aphasic seizures within the ADLTE clinical spectrum, suggest the existence of locus heterogeneity in ADLTE, and provide new familial cases with LGI1 missense mutations associated with the disease.

Oscillucusis and sudden deafness in a migraine patient

Migraine is a complex disease that includes neurologic, gastrointestinal and autonomic symptoms, although headache is most common feature. In a portion of cases headache is preceded by focal neurologic symptoms termed auras. Auditory symptoms only rarely occur as part of an aura. We describe a patient whose 13-year migraine history that included the abnormal perception an oscillation of the intensity of ambient sounds (oscillucusis). During a migraine attack immediately after oscillucusis, the patient developed acute and permanent sudden deafness. Clinical and neurologic examinations revealed only profound hearing loss in her left ear. Audiometric testing confirmed the sensorineural nature of the hearing loss. The clinical aspects and physiopathology of auditory symptoms in this case and in patients with migraine is reviewed.

Evidence for distinct genetic influences on generalized and localization-related epilepsy

PURPOSE

Determining the existence of syndrome-specific genetic factors in epilepsy is essential for phenotype definition in genetic linkage studies, and informs research on basic mechanisms. Analysis of concordance of epilepsy syndromes in families has been used to assess shared versus distinct genetic influences on generalized epilepsy (GE) and localization-related epilepsy (LRE). However, it is unclear how the results should be interpreted in relation to specific genetic hypotheses.

METHODS

To assess evidence for distinct genetic influences on GE and LRE, we examined concordance of GE and LRE in 63 families containing multiple individuals with idiopathic or cryptogenic epilepsy, drawn from the Epilepsy Family Study of Columbia University. To control for the number of concordant families expected by chance, we used a permutation test to compare the observed number with the number expected from the distribution of individuals with GE and LRE in the study families.

RESULTS

Of the families, 62% were concordant for epilepsy type, and 38% were discordant. In all analyses, the proportion of concordant families was significantly greater than expected.

CONCLUSIONS

This suggests that some genetic influences predispose specifically to either GE or LRE. Because of the ascertainment bias resulting from the selection of families containing multiple individuals with epilepsy, we could not test whether there are also shared genetic influences on these two epilepsy subtypes. Population-based studies will be needed to explore these results further.

Mutations in LGI1 cause autosomal-dominant partial epilepsy with auditory features

The epilepsies are a common, clinically heterogeneous group of disorders defined by recurrent unprovoked seizures. Here we describe identification of the causative gene in autosomal-dominant partial epilepsy with auditory features (ADPEAF, MIM 600512), a rare form of idiopathic lateral temporal lobe epilepsy characterized by partial seizures with auditory disturbances. We constructed a complete, 4.2-Mb physical map across the genetically implicated disease-gene region, identified 28 putative genes (Fig. 1) and resequenced all or part of 21 genes before identifying presumptive mutations in one copy of the leucine-rich, glioma-inactivated 1 gene (LGI1) in each of five families with ADPEAF. Previous studies have indicated that loss of both copies of LGI1 promotes glial tumor progression. We show that the expression pattern of mouse Lgi1 is predominantly neuronal and is consistent with the anatomic regions involved in temporal lobe epilepsy. Discovery of LGI1 as a cause of ADPEAF suggests new avenues for research on pathogenic mechanisms of idiopathic epilepsies.