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

Case Report: Stereoelectroencephalography and Stereoelectroencephalography-Guided Radiofrequency Thermocoagulation in Familial Lateral Temporal Lobe Epilepsy

Familial lateral temporal lobe epilepsy (FLTLE) is genetic focal epilepsy usually characterised by auditory symptoms. Most FLTLE cases can be controlled by anti-seizure medications, and to our best knowledge, there are no previous reports about stereoelectroencephalography (SEEG) used for patients with FLTLE. In this report, we present two patients with FLTLE in one family and their SEEG performances, together with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET and MRI results. In case 1, fast activities originated from the right superior temporal gyrus and spread rapidly to the right anterior insular lobe and hippocampus. In case 2, there were two seizure patterns: (1) The fast activities or sharp slow waves were identified at the left superior temporal gyrus, then, sharp waves and spike waves spread in the left superior temporal gyrus; (2) There were fast activities and slow-wave oscillation originated in the left superior temporal gyrus, then, the fast activities spread in the left superior temporal gyrus and finally spread to the other sites. An SEEG-guided radiofrequency thermocoagulation was performed for both patients and one of them underwent resection surgery. Seizures are well-controlled and the patients are very satisfied with the therapeutic effects.

The Kainic Acid Models of Temporal Lobe Epilepsy

Experimental models of epilepsy are useful to identify potential mechanisms of epileptogenesis, seizure genesis, comorbidities, and treatment efficacy. The kainic acid (KA) model is one of the most commonly used. Several modes of administration of KA exist, each producing different effects in a strain-, species-, gender-, and age-dependent manner. In this review, we discuss the advantages and limitations of the various forms of KA administration (systemic, intrahippocampal, and intranasal), as well as the histologic, electrophysiological, and behavioral outcomes in different strains and species. We attempt a personal perspective and discuss areas where work is needed. The diversity of KA models and their outcomes offers researchers a rich palette of phenotypes, which may be relevant to specific traits found in patients with temporal lobe epilepsy.

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.

Lack of association of childhood partial epilepsy with brain derived neurotrophic factor gene

Brain-derived factor (BDNF) is a member of neurotrophin family and is localized and upregulated in areas implicated in epileptogenesis. Several lines of evidence make the BDNF gene a plausible candidate gene for predisposition to epilepsy. In this study, we tested that BDNF might be involved in the etiology of childhood PE. To assess whether BDNF gene C270T polimorphism could be implicated in vulnerability to PE, we conducted a case-control association analysis (112 partial epileptic and 100 controls) in Turkish children. Epileptic children were divided into two groups: 1—idiopathic (n = 85) and 2—symptomathic epilepsy (n = 27). There was no significant difference in genotypic distribution and allelic frequencies of the BDNF gene C270T polimorphism between the PE and control groups. However, the BDNF gene TT genotype was more frequently seen in the epileptic children (15 versus 11 patients, resp.). Interestingly, in the epilepsy group, both two children with TT genotype have posttraumatic epilepsy. The data indicate a possible association with the 270T genotype of the BDNF gene with a posttraumatic epilepsy. To draw any conclusion, further studies using larger sample sizes should be carried out in various ethnic populations in childhood epilepsies.

Temporal lobe epilepsy semiology

Epilepsy represents a multifaceted group of disorders divided into two broad categories, partial and generalized, based on the seizure onset zone. The identification of the neuroanatomic site of seizure onset depends on delineation of seizure semiology by a careful history together with video-EEG, and a variety of neuroimaging technologies such as MRI, fMRI, FDG-PET, MEG, or invasive intracranial EEG recording. Temporal lobe epilepsy (TLE) is the commonest form of focal epilepsy and represents almost 2/3 of cases of intractable epilepsy managed surgically. A history of febrile seizures (especially complex febrile seizures) is common in TLE and is frequently associated with mesial temporal sclerosis (the commonest form of TLE). Seizure auras occur in many TLE patients and often exhibit features that are relatively specific for TLE but few are of lateralizing value. Automatisms, however, often have lateralizing significance. Careful study of seizure semiology remains invaluable in addressing the search for the seizure onset zone.

Diagnosis and treatment of paroxysmal dyskinesias revisited

Paroxysmal dyskinesias (PDs) are a rare group of hyperkinetic movement disorders mainly characterized by their episodic nature. Neurological examination may be entirely normal between the attacks. Three main types of PDs can be distinguished based on their precipitating events - (i) paroxysmal kinesigenic dyskinesias (PKD), (ii) paroxysmal non-kinesigenic dyskinesias (PNKD) and (iii) paroxysmal exercise-induced (exertion-induced) dyskinesias (PED). The diagnosis of PDs is based on their clinical presentation and precipitating events. Substantial progress has been made in the field of genetics and PDs. Treatment options mainly include anticonvulsants and benefit of treatment is depending on the type of PD. Most important differential diagnosis are non-epileptic psychogenic, non-epileptic organic and epileptic attack disorders, especially nocturnal frontal lobe epilepsy.

Mutational analysis of SCN2B, SCN3B and SCN4B in a large Chinese Han family with generalized tonic-clonic seizure

Voltage-gated sodium channel genes are associated with idiopathic generalized epilepsy. Our group preciously identified a suggestive new locus on chromosome 11q22.1-23.3 in a five-generational Chinese epileptic family with generalized tonic-clonic seizure. SCN2B, SCN3B and SCN4B, which located at 11q22.1-23.3 locus, were chosen as candidate genes for this family. In the present study, genomic DNA was extracted in six affected family members. All exons of SCN2B, SCN3B and SCN4B were sequenced using direct DNA sequence analysis. The results showed that no mutation or polymorphism of coding regions of SCN2B, SCN3B and SCN4B was detected in the tested family members. Therefore, SCN2B, SCN3B and SCN4B are not major susceptibility genes contributed to our large family.

Focal epilepsy in the Belgian shepherd: evidence for simple Mendelian inheritance

OBJECTIVES

To establish the mode of inheritance and describe the clinical features of epilepsy in the Belgian shepherd, taking the outset in an extended Danish dog family (199 individuals) of Groenendael and Tervueren with accumulated epilepsy.

METHODS

Epilepsy positive individuals (living and deceased) were ascertained through a telephone interview using a standardised questionnaire regarding seizure history and phenomenology. Living dogs were invited to a detailed clinical evaluation. Litters more than five years of age, or where epilepsy was present in all offspring before the age of five, were included in the calculations of inheritance. results: Out of 199 family members, 66 dogs suffered from epilepsy. The prevalence of epilepsy in the family was 33%. Fifty-five dogs experienced focal seizures with or without secondary generalisation, while four dogs experienced primary generalised seizures. In seven dogs, seizures could not be classified. The mode of inheritance of epilepsy was simple Mendelian.

CLINICAL SIGNIFICANCE

This study identified that the Belgian shepherd suffers from genetically transmitted focal epilepsy. The seizure phenomenology expressed by family members have a strong resemblance to what has been reported for familial partial (focal) epilepsy in humans with variable foci with suggestion of linkage to chromosome 2 and chromosome 22q12.

Kv4.2 knockout mice demonstrate increased susceptibility to convulsant stimulation

PURPOSE

Kv4.2 subunits contribute to the pore-forming region of channels that express a transient, A-type K(+) current (A-current) in hippocampal CA1 pyramidal cell dendrites. Here, the A-current plays an important role in signal processing and synaptic integration. Kv4.2 knockout mice show a near elimination of the A-current in area CA1 dendrites, producing increased excitability in this region. In these studies, we evaluated young adult Kv4.2 knockout mice for spontaneous seizures and the response to convulsant stimulation in the whole animal in vivo and in hippocampal slices in vitro.

METHODS

Electroencephalogram electrode-implanted Kv4.2 knockout and wild-type mice were observed for spontaneous behavioral and electrographic seizures. The latency to seizure and status epilepticus onset in Kv4.2 knockout and wild-type mice was assessed following intraperitoneal injection of kainate. Extracellular field potential recordings were performed in hippocampal slices from Kv4.2 knockout and wild-type mice following the bath application of bicuculline.

RESULTS

No spontaneous behavioral or electrographic seizures were observed in Kv4.2 knockout mice. Following kainate, Kv4.2 knockout mice demonstrated a decreased seizure and status epilepticus latency as well as increased mortality compared to wild-type littermates. The background strain modified the seizure susceptibility phenotype in Kv4.2 knockout mice. In response to bicuculline, slices from Kv4.2 knockout mice exhibited an increase in epileptiform bursting in area CA1 as compared to wild-type littermates.

DISCUSSION

These studies show that loss of Kv4.2 channels is associated with enhanced susceptibility to convulsant stimulation, supporting the concept that Kv4.2 deficiency may contribute to aberrant network excitability and regulate seizure threshold.

Genes associated with idiopathic epilepsies: a current overview

OBJECTIVE

This article aimed to review the latest genes associated with idiopathic focal and generalized epilepsies.

METHODS

PubMed and Entrez Gene searches pertaining to this work was conducted using specific keyword search terms related to genes and various listed subtopics related to idiopathic epilepsy syndromes.

RESULTS

Mutations in the cholinergic receptor, neuronal nicotinic, alpha2, alpha4 and beta2 subunit genes have been found in autosomal dominant nocturnal frontal lobe epilepsy. Mutations of potassium voltage-gated channel, KQT-like subfamily, members 2 and 3 genes were identified to be responsible for benign familial neonatal seizures. The voltage-gated sodium channel genes and gamma-aminobutyric acid receptor alpha subunit genes may be involved in the pathogenesis of generalized epilepsy with febrile seizure plus. Mutations of gamma-aminobutyric acid receptor alpha1, gamma-aminobutyric acid receptor delta, calcium channel voltage-dependent beta4 subunit and chloride channel 2 gene are associated with juvenile myoclonic epilepsy. In addition, mutations of leucine-rich, glioma-inactivated 1 gene leads to genetic abnormalities of familial lateral temporal lobe epilepsy. EF-hand domain (C-terminal)-containing 1 gene can cause some patterns of juvenile myoclonic and juvenile absence epilepsies.

DISCUSSION

Genetic factors play an important role in idiopathic epilepsy syndromes. Ion channel genes and some non-ion channel genes contribute to the pathogenesis of idiopathic epilepsies. Based on these findings, genetic diagnosis and new treatment strategies to part of idiopathic epilepsies become possible in the future.

Molecular and cellular basis of epileptogenesis in symptomatic epilepsy

Epileptogenesis refers to a process in which an initial brain-damaging insult triggers a cascade of molecular and cellular changes that eventually lead to the occurrence of spontaneous seizures. Cellular alterations include neurodegeneration, neurogenesis, axonal sprouting, axonal injury, dendritic remodeling, gliosis, invasion of inflammatory cells, angiogenesis, alterations in extracellular matrix, and acquired channelopathies. Large-scale molecular profiling of epileptogenic tissue has provided information about the molecular pathways that can initiate and maintain cellular alterations. Currently we are learning how these pathways contribute to postinjury epileptogenesis and recovery process and whether they could be used as treatment targets.

Advancements in the Treatment of Epilepsy

Diagnostic tools and treatment options for epilepsy have expanded in recent years. Imaging techniques once confined to research laboratories are now routinely used for clinical purposes. Medications that were unavailable a few years ago are now first-line agents. Patients with refractory seizures push for earlier surgical intervention, consider treatment with medical devices, and actively seek nonpharmacologic alternatives. We review some of these recent advances in the management of epilepsy.