Familial temporal lobe epilepsy with febrile seizures

Missense variants in ANO4 cause sporadic encephalopathic or familial epilepsy with evidence for a dominant-negative effect

Anoctamins are a family of Ca2+-activated proteins that may act as ion channels and/or phospholipid scramblases with limited understanding of function and disease association. Here, we identified five de novo and two inherited missense variants in ANO4 (alias TMEM16D) as a cause of fever-sensitive developmental and epileptic or epileptic encephalopathy (DEE/EE) and generalized epilepsy with febrile seizures plus (GEFS+) or temporal lobe epilepsy. In silico modeling of the ANO4 structure predicted that all identified variants lead to destabilization of the ANO4 structure. Four variants are localized close to the Ca2+ binding sites of ANO4, suggesting impaired protein function. Variant mapping to the protein topology suggests a preliminary genotype-phenotype correlation. Moreover, the observation of a heterozygous ANO4 deletion in a healthy individual suggests a dysfunctional protein as disease mechanism rather than haploinsufficiency. To test this hypothesis, we examined mutant ANO4 functional properties in a heterologous expression system by patch-clamp recordings, immunocytochemistry, and surface expression of annexin A5 as a measure of phosphatidylserine scramblase activity. All ANO4 variants showed severe loss of ion channel function and DEE/EE associated variants presented mild loss of surface expression due to impaired plasma membrane trafficking. Increased levels of Ca2+-independent annexin A5 at the cell surface suggested an increased apoptosis rate in DEE-mutant expressing cells, but no changes in Ca2+-dependent scramblase activity were observed. Co-transfection with ANO4 wild-type suggested a dominant-negative effect. In summary, we expand the genetic base for both encephalopathic sporadic and inherited fever-sensitive epilepsies and link germline variants in ANO4 to a hereditary disease.

Considering the Role of Extracellular Matrix Molecules, in Particular Reelin, in Granule Cell Dispersion Related to Temporal Lobe Epilepsy

The extracellular matrix (ECM) of the nervous system can be considered as a dynamically adaptable compartment between neuronal cells, in particular neurons and glial cells, that participates in physiological functions of the nervous system. It is mainly composed of carbohydrates and proteins that are secreted by the different kinds of cell types found in the nervous system, in particular neurons and glial cells, but also other cell types, such as pericytes of capillaries, ependymocytes and meningeal cells. ECM molecules participate in developmental processes, synaptic plasticity, neurodegeneration and regenerative processes. As an example, the ECM of the hippocampal formation is involved in degenerative and adaptive processes related to epilepsy. The role of various components of the ECM has been explored extensively. In particular, the ECM protein reelin, well known for orchestrating the formation of neuronal layer formation in the cerebral cortex, is also considered as a player involved in the occurrence of postnatal granule cell dispersion (GCD), a morphologically peculiar feature frequently observed in hippocampal tissue from epileptic patients. Possible causes and consequences of GCD have been studied in various in vivo and in vitro models. The present review discusses different interpretations of GCD and different views on the role of ECM protein reelin in the formation of this morphological peculiarity.

Molecular typing of familial temporal lobe epilepsy

The pathogenesis of temporal lobe epilepsy (TLE) was originally considered to be acquired. However, some reports showed that TLE was clustered in some families, indicating a genetic etiology. With the popularity of genetic testing technology, eleven different types of familial TLE (FTLE), including ETL1-ETL11, have been reported, of which ETL9-ETL11 had not yet been included in the OMIM database. These types of FTLE were caused by different genes/Loci and had distinct characteristics. ETL1, ETL7 and ETL10 were characterized by auditory, visual and aphasia seizures, leading to the diagnosis of familial lateral TLE. ETL2, ETL3 and ETL6 showed prominent autonomic symptom and automatism with or without hippocampal abnormalities, indicating a mesial temporal origin. Febrile seizures were common in FTLEs such as ETL2, ETL5, ETL6 and ETL11. ETL4 was diagnosed as occipitotemporal lobe epilepsy with a high incidence of migraine and visual aura. Considering the diversity and complexity of the symptoms of TLE, neurologists enquiring about the family history of epilepsy should ask whether the relatives of the proband had experienced unnoticeable seizures and whether there is a family history of other neurological diseases carefully. Most FTLE patients had a good prognosis with or without anti-seizure medication treatment, with the exception of patients with heterozygous mutations of the CPA6 gene. The pathogenic mechanism was diverse among these genes and spans disturbances of neuron development, differentiation and synaptic signaling. In this article, we describe the research progress on eleven different types of FTLE. The precise molecular typing of FTLE would facilitate the diagnosis and treatment of FTLE and genetic counseling for this disorder.

Hippocampal Malrotation: A Genetic Developmental Anomaly Related to Epilepsy?

Hippocampal malrotation (HIMAL) is an increasingly recognized neuroimaging feature but the clinical correlation and significance in epilepsies remain under debate. It is characterized by rounded hippocampal shape, deep collateral, or occipitotemporal sulcus, and medial localization of the hippocampus. In this review, we describe the embryonic development of the hippocampus and HIMAL, the qualitative and quantitative diagnosis issues, and the pathological findings of HIMAL. HIMAL can be bilateral or unilateral and more on the left side. Furthermore, the relevance of HIMAL diagnosis in clinical practice, including its role in epileptogenesis and the impact on the pre-surgical decision are reviewed. Finally, the relationship between HIMAL and hippocampal sclerosis (HS) and the possible role of genetics in the etiology of HIMAL are discussed. The evidence so far suggested that HIMAL does not have a significant role in epileptogenesis or surgical decision. HIMAL could be a genetic developmental imaging feature that represents a more diffuse but subtle structural error during brain development. Many questions remain to be explored, such as possible cognitive alteration associated with HIMAL and whether HIMAL predisposes to the development of HS. Further studies using high-quality MRI, unified consensus qualitative and quantitative diagnostic criteria, and comprehensive cognitive assessment are recommended.

Familial mesial temporal lobe epilepsy in Mexico: Inheritance pattern and clinical features

PURPOSE

The objectives of this study were to determine the inheritance pattern by which familial mesial temporal lobe epilepsy (FMTLE) is segregated in Mexican families, and to identify if there was an association between the clinical characteristics and the inheritance pattern.

METHOD

We included a total of 25 families with two or more members affected with MTLE during two years and elaborated a family pedigree for each family. The inheritance pattern was classified as autosomal dominant (AD) or autosomal recessive (AR), considering the affected members. We used statistical analysis association and differences between clinical characteristics and inheritance patterns.

RESULTS

The affected families with the AD pattern were 15.7 fold times more likely to start seizures at 5 years of age or earlier than families with AR pattern, OR = 15.7 (IC 95% = 1.9-128.9). We observed a predominance and greater déjà vu association (64.4% vs 31.3%; p = 0.021), OR = 3.9 (CI 95% = 1.1-13.5) in patients with AD versus AR pattern. Finally, we identified that patients with AD pattern had a likelihood of presenting emotional alterations 5.6 times higher than AR (OR = 5.6, IC = 1.1-27.5).

CONCLUSION

FMTLE is a heterogeneous syndrome, both phenotypically and genotypically; thus, our findings may be helpful for clinical use to perform an early diagnosis, to provide timely treatment, and to prevent comorbidities associated to this disease. However, in order to identify the possible genetic causes underlying these inheritance patterns, the use of molecular studies is necessary.

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 new locus for familial temporal lobe epilepsy on chromosome 3q

BACKGROUND

Temporal lobe epilepsy (TLE) is a common and heterogeneous focal epilepsy syndrome with a complex etiology, involving both environmental and genetic factors. Several familial forms of TLE have been described, including familial lateral TLE (FLTLE), familial mesial TLE (FMTLE) without hippocampal sclerosis, and FMTLE with hippocampal sclerosis. Mutations have been identified only in the leucine-rich, glioma-inactivated 1 (LGI1) gene on chromosome 10q22-q24 in FLTLE. Several loci have been mapped in families with FMTLE, but responsible genes have not been found. We report clinical evaluation in a large family with FMTLE and a new genetic locus.

METHODS

We conducted a genome-wide scan using 10cM-spaced microsatellite markers on a family with TLE. Seven individuals had TLE without antecedent FS; four other individuals had FS during childhood, but no subsequent epilepsy. Patients with TLE had infrequent simple partial, complex partial and secondarily generalized seizures that generally responded well to treatment. The proband had no hippocampal sclerosis. The mode of inheritance appeared to be autosomal dominant with incomplete penetrance. Linkage analysis was performed using the Genehunter software. Regions with LOD score>1 and those that were poorly informative in the first-pass scan were further genotyped.

RESULTS

Linkage was identified on chromosome 3q25-q26 in a 13cM region flanked by markers D3S1584 and D3S3520, with a peak LOD score of 3.23. This interval does not correspond to any previously known locus for familial epilepsy or FS. KCNAB1, encoding a voltage-gated, shaker-related potassium channel, and NLGN1, encoding a member of a family of neuronal cell surface protein were excluded as disease causing mutations.

CONCLUSION

We identified a novel locus for familial TLE with FS, providing additional evidence of the complexity and genetic heterogeneity of familial focal epilepsy.

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.

Automatic hippocampal segmentation in temporal lobe epilepsy: impact of developmental abnormalities

In drug-resistant temporal lobe epilepsy (TLE), detecting hippocampal atrophy on MRI is important as it allows defining the surgical target. The performance of automatic segmentation in TLE has so far been considered unsatisfactory. In addition to atrophy, about 40% of patients present with developmental abnormalities (referred to as malrotation) characterized by atypical morphologies of the hippocampus and collateral sulcus. Our purpose was to evaluate the impact of malrotation and atrophy on the performance of three state-of-the-art automated algorithms. We segmented the hippocampus in 66 patients and 35 sex- and age-matched healthy subjects using a region-growing algorithm constrained by anatomical priors (SACHA), a freely available atlas-based software (FreeSurfer) and a multi-atlas approach (ANIMAL-multi). To quantify malrotation, we generated 3D models from manual hippocampal labels and automatically extracted collateral sulci. The accuracy of automated techniques was evaluated relative to manual labeling using the Dice similarity index and surface-based shape mapping, for which we computed vertex-wise displacement vectors between automated and manual segmentations. We then correlated segmentation accuracy with malrotation features and atrophy. ANIMAL-multi demonstrated similar accuracy in patients and healthy controls (p > 0.1), whereas SACHA and FreeSurfer were less accurate in patients (p < 0.05). Surface-based analysis of contour accuracy revealed that SACHA over-estimated the lateral border of malrotated hippocampi (r = 0.61; p < 0.0001), but performed well in the presence of atrophy (|r |< 0.34; p > 0.2). Conversely, FreeSurfer and ANIMAL-multi were affected by both malrotation (FreeSurfer: r = 0.57; p = 0.02, ANIMAL-multi: r = 0.50; p = 0.05) and atrophy (FreeSurfer: r = 0.78, p < 0.0001, ANIMAL-multi: r = 0.61; p < 0.0001). Compared to manual volumetry, automated procedures underestimated the magnitude of atrophy (Cohen's d: manual: 1.68; ANIMAL-multi: 1.11; SACHA: 1.10; FreeSurfer: 0.90, p < 0.0001). In addition, they tended to lateralize the seizure focus less accurately in the presence of malrotation (manual: 64%; ANIMAL-multi: 55%, p = 0.4; SACHA: 50%, p = 0.1; FreeSurfer: 41%, p = 0.05). Hippocampal developmental anomalies and atrophy had a negative impact on the segmentation performance of three state-of-the-art automated methods. These shape variants should be taken into account when designing segmentation algorithms.

The first genome-wide scan in a tunisian family with generalized epilepsy with febrile seizure plus (GEFS+)

Generalized epilepsy with febrile seizure plus (GEFS+) is an autosomal dominant disorder. In the literature, 5 responsible genes were identified and 2 novel susceptibility loci for GEFS+ at 2p24 and 8p23-p21 were reported, indicating the genetic heterogeneity of this disorder. The aim of this report is to identify the responsible loci in a large affected Tunisian family by performing a 10cM density genome-wide scan. The highest multipoint logarithm of odds (LOD) score (1.04) was found for D5S407 in the absence of recombination. Two other interesting regions were found around marker D19S210 (LOD=0.799) and D7S484 (LOD=0.61) markers. To fine map these loci, additional markers in 2 regions on 5q13.3 and 7p14.2 were analyzed and positive LOD scores for both loci were obtained. Sequencing of the Sodium channel subunit beta-1 gene (SCN1B) (19q13.1) showed the absence of any causal mutation. Our findings emphasized the genetic heterogeneity of febrile seizures.

Familial mesial temporal lobe epilepsy: a benign epilepsy syndrome showing complex inheritance

Temporal lobe epilepsy is the commonest partial epilepsy of adulthood. Although generally perceived as an acquired disorder, several forms of familial temporal lobe epilepsy, with mesial or lateral seizure semiology, have been described. Descriptions of familial mesial temporal lobe epilepsy have varied widely from a benign epilepsy syndrome with prominent déjà vu and without antecedent febrile seizures or magnetic resonance imaging abnormalities, to heterogeneous, but generally more refractory epilepsies, often with a history of febrile seizures and with frequent hippocampal atrophy and high T₂ signal on magnetic resonance imaging. Compelling evidence of a genetic aetiology (rather than chance aggregation) in familial mesial temporal lobe epilepsy has come from twin studies. Dominant inheritance has been reported in two large families, though the usual mode of inheritance is not known. Here, we describe clinical and neurophysiological features of 20 new mesial temporal lobe epilepsy families including 51 affected individuals. The epilepsies in these families were generally benign, and febrile seizure history was infrequent (9.8%). No evidence of hippocampal sclerosis or dysplasia was present on brain imaging. A single individual underwent anterior temporal lobectomy, with subsequent seizure freedom and histopathological evidence of hippocampal sclerosis was not found. Inheritance patterns in probands' relatives were analysed in these families, together with 19 other temporal lobe epilepsy families previously reported by us. Observed frequencies of epilepsies in relatives were lower than predicted by dominant Mendelian models, while only a minority (8/39) of families could be compatible with recessive inheritance. These findings strongly suggest that complex inheritance, similar to that widely accepted in the idiopathic generalized epilepsies, is the usual mode of inheritance in familial mesial temporal lobe epilepsy. This disorder, which appears to be relatively common, and not typically associated with hippocampal sclerosis, is an appropriate target for contemporary approaches to complex disorders such as genome-wide association studies for common genetic variants or deep sequencing for rare variants.

Functional variant in complement C3 gene promoter and genetic susceptibility to temporal lobe epilepsy and febrile seizures

Background

Human mesial temporal lobe epilepsies (MTLE) represent the most frequent form of partial epilepsies and are frequently preceded by febrile seizures (FS) in infancy and early childhood. Genetic associations of several complement genes including its central component C3 with disorders of the central nervous system, and the existence of C3 dysregulation in the epilepsies and in the MTLE particularly, make it the C3 gene a good candidate for human MTLE.

Methodology/Principal Findings

A case-control association study of the C3 gene was performed in a first series of 122 patients with MTLE and 196 controls. Four haplotypes (HAP1 to 4) comprising GF100472, a newly discovered dinucleotide repeat polymorphism [(CA)8 to (CA)15] in the C3 promoter region showed significant association after Bonferroni correction, in the subgroup of MTLE patients having a personal history of FS (MTLE-FS+). Replication analysis in independent patients and controls confirmed that the rare HAP4 haplotype comprising the minimal length allele of GF100472 [(CA)8], protected against MTLE-FS+. A fifth haplotype (HAP5) with medium-size (CA)11 allele of GF100472 displayed four times higher frequency in controls than in the first cohort of MTLE-FS+ and showed a protective effect against FS through a high statistical significance in an independent population of 97 pure FS. Consistently, (CA)11 allele by its own protected against pure FS in a second group of 148 FS patients. Reporter gene assays showed that GF100472 significantly influenced C3 promoter activity (the higher the number of repeats, the lower the transcriptional activity). Taken together, the consistent genetic data and the functional analysis presented here indicate that a newly-identified and functional polymorphism in the promoter of the complement C3 gene might participate in the genetic susceptibility to human MTLE with a history of FS, and to pure FS.

Conclusions/Significance

The present study provides important data suggesting for the first time the involvement of the complement system in the genetic susceptibility to epileptic seizures and to epilepsy.

Hippocampal malrotation in pediatric patients with epilepsy associated with complex prefrontal dysfunction

PURPOSE

The cognitive consequences of hippocampal malrotation (HIMAL) were investigated in a matched control study of children with epilepsy.

METHODS

Seven children with HIMAL were compared on a range of memory and attention tasks with 21 control children with epilepsy without temporal role pathology and 7 children with epilepsy and magnetic resonance imaging (MRI)-documented hippocampal sclerosis. In addition, in a statistical morphometric analysis, MRI studies from four children with HIMAL were compared to similar images of 20 age-matched typically developing control children.

RESULTS

Although the task battery was sensitive to the memory deficit of the children with hippocampal sclerosis, it did not reveal memory impairment in the patients with HIMAL. In contrast, the patients with HIMAL were impaired on the attentionally more demanding dual tasks, compared to both the control and the hippocampal sclerosis group. The structural MRI analysis revealed morphometric abnormalities in the tail of the affected hippocampus, the adjacent neocortex, and the ipsilateral medial thalamus. The basal forebrain was bilaterally affected. Abnormalities in remote cortex were found in the ipsilateral temporal lobe, the contralateral anterior cingulate gyrus, and bilateral in the dorsolateral and lateral-orbitofrontal prefrontal cortex.

DISCUSSION

Because the prefrontal cortical regions have been shown to be active during dual-task performance, the MRI results converge with the neuropsychological findings of impairment on these tasks. We conclude that HIMAL had no direct memory repercussions, but was secondary to subtle but widespread neurologic abnormalities that also affected morphology and functioning of the prefrontal cortex.

Sudden death, febrile seizures, and hippocampal and temporal lobe maldevelopment in toddlers: a new entity

Recently, we reported hippocampal and temporal lobe abnormalities in 5 toddlers with sudden unexplained death in childhood (SUDC). The association of these anomalies with a high incidence (40%) of individual/family histories of simple febrile seizures in the cases raised concern that febrile seizures can be associated with death. In a series of 64 toddlers with sudden death, we tested the hypothesis that an SUDC subset is characterized by hippocampal and temporal lobe maldevelopment and an individual and/or family history of simple familial seizures. Cases of sudden and unexplained death in children aged 1.0 to 5.9 years (median 1.7 years) were divided into groups based upon a history of febrile or nonfebrile seizures, familial febrile seizures, and autopsy classification of cause of death. Forty-nine of the 64 cases (77%) were classified as SUDC, of which 40% had an individual/family history of febrile seizures. Of the 26 SUDC cases with available hippocampal sections, 62% (16/26) had hippocampal and temporal lobe anomalies, including 82% (9/11) of cases with an individual/family history of febrile seizures. Cases with these anomalies were all found dead during a sleep period, typically in the prone (87%) position. We conclude that a potential new entity may account for the majority of SUDC in toddlers, defined by sleep-related death in the prone position, individual/family history of febrile seizures, and hippocampal and temporal lobe anomalies. The mechanism of death appears analogous to sudden death in (temporal lobe) epilepsy, with a putative unwitnessed seizure during sleep leading to airway occlusion and death. This study mandates further research into the potential link between simple febrile seizures and death.

Familial mesial temporal lobe epilepsy (FMTLE) : a clinical and genetic study of 15 Italian families

INTRODUCTION

Familial mesial temporal lobe epilepsy (FMTLE) is characterized by prominent psychic and autonomic seizures, often without hippocampal sclerosis (HS) or a previous history of febrile seizures (FS), and good prognosis. The genetics of this condition is largely unknown.We present the electroclinical and genetic findings of 15 MTLE Italian families.

PATIENTS AND METHODS

FMTLE was defined when two or more first-degree relatives had epilepsy suggesting a mesial temporal lobe origin. The occurrence of seizures with auditory auras was considered an exclusion criterion. Patients underwent video-EEG recordings, 1.5-Tesla MRI particularly focused on hippocampal analysis, and neuropsychological evaluation. Genetic study included genotyping and linkage analysis of candidate loci at 4q, 18q, 1q, and 12q as well as screening for LGI1/Epitempin mutations.

RESULTS

Most of the families showed an autosomal dominant inheritance pattern with incomplete penetrance. Fifty-four (32 F) affected individuals were investigated. Twenty-one (38.8 %) individuals experienced early FS. Forty-eight individuals fulfilled the criteria for MTLE. Epigastric/visceral sensation (72.9 %) was the most common type of aura, followed by psychic symptoms (35.4 %), and déjà vu (31.2 %). HS occurred in 13.8% of individuals, three of whom belonged to the same family. Prognosis of epilepsy was generally good. Genetic study failed to show LGI1/Epitempin mutations or significative linkage to the investigated loci.

DISCUSSION

FMTLE may be a more common than expected condition, clinically and genetically heterogeneous. Some of the reported families, grouped on the basis of a specific aura, may represent an interesting subgroup on whom to focus future linkage studies.

Early seizures: causal events or predisposition to adult epilepsy?

Past studies have been unable to confirm whether early seizures predispose to epilepsy in adults. Seizures in infancy were classically thought to cause brain lesions that led to epilepsy in adulthood. However, these infants were not thought to have epilepsy, but acute events that included seizures. Accumulating evidence suggests that early seizures may be associated with, or cause, brain damage; or alternatively, they may be the first expression of a genetic or lesional predisposition to epilepsy. The course of early seizures ranges from transient to life-long, depending on epilepsy syndrome, causes, and treatment. The main factors that determine late or persisting epilepsy after the occurrence of early seizures are protracted seizures, tonic seizures, and involvement of mesial temporal structures. A developmental approach to seizure disorders will aid understanding of epilepsy in adults and improve the design of antiepileptic agents for children and adults.

Sudden death in toddlers associated with developmental abnormalities of the hippocampus: a report of five cases

Sudden unexplained death in childhood (SUDC) is the sudden death of a child older than 1 year of age that remains unexplained after review of the clinical history, circumstances of death, and autopsy with appropriate ancillary testing. We report here 5 cases of SUDC in toddlers that we believe define a new entity associated with hippocampal anomalies at autopsy. All of the toddlers died unexpectedly during the night, apparently during sleep. Within 48 hours before death, 2 toddlers had fever, 3 had a minor upper respiratory tract infection, and 3 experienced minor head trauma. There was a history of febrile seizures in 2 (40%) and a family history of febrile seizures in 2 (40%). Hippocampal findings included external asymmetry and 2 or more microdysgenetic features. The incidence of certain microdysgenetic features was substantially increased in the temporal lobes of these 5 cases compared with the temporal lobes of 39 (control) toddlers with the causes of death established at autopsy (P < 0.01). We propose that these 5 cases define a potential subset of SUDC whose sudden death is caused by an unwitnessed seizure arising during sleep in the anomalous hippocampus and producing cardiopulmonary arrest. Precipitating factors may be fever, infection, and/or minor head trauma. Suggested risk factors are a history of febrile seizures and/or a family history of febrile seizures. Future studies are needed to confirm these initial findings and to define the putative links between sudden death, hippocampal anomalies, and febrile seizures in toddlers.

Phenotype definition in epilepsy

Phenotype definition consists of the use of epidemiologic, biological, molecular, or computational methods to systematically select features of a disorder that might result from distinct genetic influences. By carefully defining the target phenotype, or dividing the sample by phenotypic characteristics, we can hope to narrow the range of genes that influence risk for the trait in the study population, thereby increasing the likelihood of finding them. In this article, fundamental issues that arise in phenotyping in epilepsy and other disorders are reviewed, and factors complicating genotype-phenotype correlation are discussed. Methods of data collection, analysis, and interpretation are addressed, focusing on epidemiologic studies. With this foundation in place, the epilepsy subtypes and clinical features that appear to have a genetic basis are described, and the epidemiologic studies that have provided evidence for the heritability of these phenotypic characteristics, supporting their use in future genetic investigations, are reviewed. Finally, several molecular approaches to phenotype definition are discussed, in which the molecular defect, rather than the clinical phenotype, is used as a starting point.

Mutations in GABRA1, GABRA5, GABRG2 and GABRD receptor genes are not a major factor in the pathogenesis of familial focal epilepsy preceded by febrile seizures

GABA(A) receptors mutations have been reported in few epilepsy families with febrile seizures (FS) followed by generalized epilepsy. It is not known if such mutations may underlie FS followed by partial epilepsy, which is a more common type of epilepsy. We searched for disease-causing mutations in the genes of the alpha1, alpha5, gamma2 and delta subunits of the GABA-A receptor that were previously shown to contain epilepsy-causing mutations or epilepsy susceptibility polymorphisms. All coding and untranslated exons of these four GABA(A) subunit genes were screened in 74 unrelated patients with familial partial epilepsy preceded by FS. Most patients had temporal lobe epilepsy (TLE). We did not detect any disease-causing mutations that would be consistent with missense, nonsense or splice site mutations in any of the four analyzed genes. We conclude that these genes are not a major genetic factor in familial TLE preceded by FS.

Genes and loci involved in febrile seizures and related epilepsy syndromes

Epilepsy is a paroxysmal disorder with a cumulative incidence of about 3%. About 13% of patients with epilepsy have a history of febrile seizures (FS). Generalized epilepsy with FS plus (GEFS+) is a familial epilepsy syndrome in which patients can have classic FS, FS that persist beyond the age of 5 years (i.e., FS+), and/or epilepsy. Both genetic and environmental factors have been shown to contribute to the pathogenesis of FS and GEFS+. During the past 10 years, molecular genetic studies have contributed a great deal to the identification of genetic factors involved in FS and GEFS+. In this study we aimed to provide a comprehensive review of currently known genes for FS and GEFS+, and the methods and approaches used to identify them. We also discuss the knowledge we currently have and hypotheses regarding the effect of the mutations on their respective protein functions.

Genetic influence on the clinical characteristics and outcome of febrile seizures--a retrospective study

PURPOSE

To assess the influence of the family history (FH) of epilepsy or febrile seizures (FSs) on the clinical presentation of FSs and on their outcome.

METHODS

We reviewed the charts of 482 children admitted to the Ste-Justine Hospital with FSs between 3 months and 6 years of age and followed for at least 5 years.

RESULTS

Children with a positive FH of epilepsy (n=67) showed significantly more focal and recurrent FSs than those without such a FH. The risk of developing partial epilepsy (n=17) or generalized epilepsy (n=19) was significantly greater in children with focal or recurrent FSs, respectively. In children with focal FSs, only two out of 30 (6.7%) children with a negative FH of epilepsy developed partial epilepsy compared with four out of nine (44.4%) children with a positive FH. In children with recurrent FSs, as much as seven out of 34 (20.6%) children with a positive FH of epilepsy developed generalized epilepsy compared to only eight out of 161 (0.05%) of those with a negative FH. Nevertheless, when not taking into account the clinical presentation of FSs, the positive FH of epilepsy constituted a risk factor for developing generalized but not partial epilepsy. Finally, children with a positive FH of FSs (n=120) exhibited significantly more recurrent FSs than those without such a FH, but this did not modify the risk of epilepsy.

CONCLUSION

The FH of FSs and/or epilepsy should be taken into account when evaluating the risk of FSs recurrence and of epilepsy.

"Tectonic" hippocampal malformations in patients with temporal lobe epilepsy

Histological analysis of hippocampi removed en bloc during surgical treatment of temporal lobe epilepsy revealed a subgroup of patients with bulbous expansions of the CA1 pyramidal cell/subicular layers that were consistently accompanied by "tectonic" invaginations of the adjacent dentate gyrus. Most hippocampi containing the CA1/subicular anomaly and the tectonically deformed dentate gyrus exhibited minor cell loss compared to hippocampi with typical hippocampal sclerosis, and retrospective analysis revealed that conventional imaging methods usually failed to detect subtle hippocampal atrophy or abnormal signal characteristics in patients with this anomaly. Cells within the anomaly exhibited the spherical appearance of undifferentiated pyramidal layer neurons, and were immunopositive for the neuronal marker NeuN. Immunostaining for the synaptic marker beta-synuclein suggested abnormal dentate gyrus lamination in segments containing the pyramidal cell layer anomaly, but not in unaffected areas of the same specimens. Despite differences in the extent of neuronal loss between patients with hippocampal sclerosis and those with the CA1/subicular anomaly, the incidence of antecedent febrile seizures was similar in both groups. In a comparison group of hippocampi obtained at autopsy, structural irregularities were evident, but were consistently less disruptive to hippocampal architecture than the anomalies observed in epilepsy patients. We hypothesize that developmental malformation of the CA1 pyramidal cell/subicular layers may adversely influence the subsequent development of the adjacent dentate gyrus, and may render temporal lobe structures hyperexcitable and more vulnerable to relatively innocuous seizures and injuries. Thus, these presumably developmental hippocampal anomalies may serve as substrates for early febrile seizures and subsequent epilepsy.

Basic mechanisms of partial epilepsies

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Febrile seizures and mesial temporal sclerosis

PURPOSE OF REVIEW

The sequence of febrile seizures followed by intractable temporal lobe epilepsy is rarely seen from a population perspective. However, several studies have shown a significant relationship between a history of prolonged febrile seizures in early childhood and mesial temporal sclerosis. The interpretation of these observations remains quite controversial. One possibility is that the early febrile seizure damages the hippocampus and is therefore a cause of mesial temporal sclerosis. Another possibility is that the child has a prolonged febrile seizure because the hippocampus was previously damaged by a prenatal or perinatal insult or by genetic predisposition.

RECENT FINDINGS

Imaging studies have shown that prolonged and focal febrile seizures can produce acute hippocampal injury that evolves to hippocampal atrophy, and that complex febrile seizures can originate in the temporal lobes in some children. Several lines of evidence now indicate that genetic predisposition is an important causal factor of febrile seizures and mesial temporal sclerosis. From recent clinical and molecular genetic studies, it appears that the relationship between febrile seizures and later epilepsy is frequently genetic, and there are several syndrome-specific genes for febrile seizures.

SUMMARY

Mesial temporal sclerosis probably has different causes. A number of retrospective studies showed that complex febrile seizures are a causative factor for the later development of mesial temporal sclerosis and temporal lobe epilepsy. However, contradictory results have come from several prospective and retrospective studies. The association between febrile seizures and temporal lobe epilepsy probably results from complex interactions between several genetic and environmental factors.

Fever, genes, and epilepsy

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

Magnetic Resonance Imaging of Familial Temporal Lobe Epilepsy

Magnetic Resonance Imaging Evidence of Hippocampal Sclerosis in Asymptomatic, First-Degree Relatives of Patients with Familial Mesial Temporal Lobe Epilepsy

Kobayashi E, Li LM, Lopes-Cendes I, Cendes F

Arch Neurol 2002;59:1891–1894

Purpose

To investigate the presence of hippocampal atrophy (HA) and other magnetic resonance imaging (MRI) signs of hippocampal sclerosis (HS) in asymptomatic relatives of patients with familial mesial temporal lobe epilepsy (FMTLE).

Methods

We invited first-degree, asymptomatic relatives of patients with FMTLE to participate in our MRI protocol. After informed consent, all participating individuals underwent an MRI examination. Hippocampal abnormality was determined by qualitative and volumetric analyses, using a standard protocol.

Results

We studied 52 asymptomatic individuals (27 men), with a mean age of 32 years (range, 7–71 years), from 11 families with FMTLE. Volumetric studies showed HA in 18 (34%) of 52 individuals: 11 had left HA, and seven had bilateral HA. In addition, careful visual analysis of T1- and T2-weighted images showed additional classic MRI signs of HS (such as abnormal T2 signal and/or abnormal internal structure) in 14 of these 18 individuals. There was no age difference between individuals with and without HA ( t test, P = 0.80).

Conclusions

Our findings indicate that MRI evidence of HS is not necessarily related to seizure severity and may occur in individuals who never had seizures. In addition, these observations strongly indicate that HS in FMTLE is not a consequence of recurrent seizures and is determined by a strong genetic predisposition. The determination of seizure severity in patients with FMTLE probably depends on the interaction of different factors, both genetic and environmental.