Genetic association analysis of KCNQ3 and juvenile myoclonic epilepsy in a South Indian population

Potassium channels in behavioral brain disorders. Molecular mechanisms and therapeutic potential: A narrative review

Potassium channels (K+-channels) selectively control the passive flow of potassium ions across biological membranes and thereby also regulate membrane excitability. Genetic variants affecting many of the human K+-channels are well known causes of Mendelian disorders within cardiology, neurology, and endocrinology. K+-channels are also primary targets of many natural toxins from poisonous organisms and drugs used within cardiology and metabolism. As genetic tools are improving and larger clinical samples are being investigated, the spectrum of clinical phenotypes implicated in K+-channels dysfunction is rapidly expanding, notably within immunology, neurosciences, and metabolism. K+-channels that previously were considered to be expressed in only a few organs and to have discrete physiological functions, have recently been found in multiple tissues and with new, unexpected functions. The pleiotropic functions and patterns of expression of K+-channels may provide additional therapeutic opportunities, along with new emerging challenges from off-target effects. Here we review the functions and therapeutic potential of K+-channels, with an emphasis on the nervous system, roles in neuropsychiatric disorders and their involvement in other organ systems and diseases.

Epilepsy: Indian perspective

There are 50 million people living with epilepsy worldwide, and most of them reside in developing countries. About 10 million persons with epilepsy are there in India. Many people with active epilepsy do not receive appropriate treatment for their condition, leading to large treatment gap. The lack of knowledge of antiepileptic drugs, poverty, cultural beliefs, stigma, poor health infrastructure, and shortage of trained professionals contribute for the treatment gap. Infectious diseases play an important role in seizures and long-term burden causing both new-onset epilepsy and status epilepticus. Proper education and appropriate health care services can make tremendous change in a country like India. There have been many original researches in various aspects of epilepsy across India. Some of the geographically specific epilepsies occur only in certain regions of our country which have been highlighted by authors. Even the pre-surgical evaluation and epilepsy surgery in patients with drug-resistant epilepsy is available in many centers in our country. This article attempts to provide a complete preview of epilepsy in India.

Role of genetics in the diagnosis and treatment of epilepsy

Epilepsy is a heterogeneous group of multifactorial diseases, the vast majority determined by interactions between many genes and environmental factors; however, there are rare epilepsy syndromes that can be caused by a single gene mutation and are inherited according to classical mendelian genetic principles. Finding disease-causing genetic mutations in epilepsy has provided new opportunities for aiding diagnosis and developing therapies. Thus, the discovery of KCNQ2 mutations in benign familial neonatal convulsions, SCN1A mutations in severe myoclonic epilepsy of infancy and in generalized epilepsy with febrile seizures plus, and CHRA4 and CHRB2 mutations in autosomal-dominant nocturnal frontal lobe epilepsy, has led to the establishment of epilepsy as a disorder of ion channel function and, furthermore, has led to the introduction of genetic tests that are available clinically to aid in diagnosis and treatment. At the present time, clinical use of genetic testing in epilepsy is greatest in suspected cases of severe myoclonic epilepsy of infancy, generalized epilepsy with febrile seizures plus, atypical cases of benign familial neonatal convulsions and 'occult' cases of autosomal-dominant nocturnal frontal lobe epilepsy without a family history. Overall, clinical use is limited by the low number of documented disease-associated mutations and the uncertain clinical significance of many test results. Further elucidation of the relationship between gene mutations and channel function will add value to genetic testing in the future, as will better characterization of the association between gene mutations and clinical phenotypes.

Juvenile myoclonic epilepsy

Juvenile myoclonus epilepsy (JME) is a common epileptic syndrome, the etiology of which is genetically determined. Its onset occurs from 6 through 22 years of age, and affected patients present with myoclonic jerks, often associated with generalized tonic-clonic seizures - the most common association - and absence seizures. JME is non-progressive, and there are no abnormalities on clinical examination or intellectual deficits. Psychiatric disorders may coexist. Generalized polyspike-and-waves are the most characteristic electroencephalographic pattern. Usual neuroimaging studies show no abnormalities. Atypical presentations should be entertained, as they are likely to induce misdiagnosis. Prevention of precipitating factors and therapy with valproic acid (VPA) are able to control seizures in the great majority of patients. Whenever VPA is judged to be inappropriate, other antiepileptic drugs such as lamotrigine may be considered. Treatment should not be withdrawn, otherwise recurrences are frequent.

Phenotypic concordance in 70 families with IGE-implications for genetic studies of epilepsy

INTRODUCTION

A crucial issue in the genetic analysis of idiopathic generalized epilepsy (IGE) is deciding on the phenotypes that are likely to give the greatest power to detect predisposing variants. A complex inheritance pattern and unclear nature of the genotype-phenotype correlation makes this task difficult. In the absence of much definitive genetic information to clarify this correlation, we inferred the putative effects of predisposing genes by studying the clustering of various phenotypic features, both clinical and electrophysiological, within families.

METHODS

We examined the distribution of clinical features among relatives of a proband in 70 French-Canadian families with a minimum of two affected individuals with a clear diagnosis of IGE and then, using concordance analysis, identified the relative genetic influences on IGE syndrome, seizure type, age-at-onset, and EEG features.

RESULTS

The mean number of affected individuals with IGE per family was three. One-third of relatives had the same syndrome as the proband. 16-22.5% of relatives of a proband with one of the absence syndromes had juvenile myoclonic epilepsy (JME). Conversely, 27% of relatives of probands with JME had an absence syndrome. 15% of relatives displayed the exact constellation of seizure types as the proband. Concordance analysis demonstrated greater clustering within families of IGE syndrome, seizure type, and age-at-onset than would be expected by chance. Significant concordance was not evident for EEG features.

DISCUSSION

There was a large degree of clinical heterogeneity present within families. However we found evidence for clustering of a number of clinical features. Further refinement of the phenotypes used in genetic studies of complex IGE is necessary for progress to be made.

Observations on juvenile myoclonic epilepsy amongst ethnic Bengalees in West Bengal—An Eastern Indian State

BACKGROUND

Juvenile myoclonic epilepsy (JME) is not too uncommonly encountered in Indian neurological practice. A number of reports from different parts of India have documented the clinical phenomenology and EEG characteristics of this genetically determined epileptic syndrome. However, no study has yet been reported from the Eastern part of India and none done so far in patients in a specific ethnic group. Furthermore therapy response and follow up data are not available in detail in the Indian studies.

OBJECTIVE

To study disease expression, EEG characteristics and therapy response of JME patients in ethnic Bengalees in West Bengal, an Eastern Indian State, in a clinic based study.

MATERIAL AND METHODS

200 patients with JME attending the Neurology Department of the Institute have been followed up for 5 years and different parameters of disease expression as outlined above have been studied.

RESULTS

Overall clinical disease expression has been found to be similar in this clinic based study in ethnic Bengalees as compared to other reports from India and elsewhere. About 16% of patients showed a relative resistance to Valproate therapy. Hundred percent of patients in whom therapy withdrawal was attempted, relapsed within<1-2 years. Amongst female patients (132), 16 developed features of polycystic ovarian syndrome while on Valproate therapy. In over half of them, the symptoms regressed after successful switch over from Valproate to Clobazam. 12/132 female patients became pregnant during follow up and while on Valproate; teratogenic effect was evident in only one such patient.

CONCLUSIONS

Phenotypic variations in disease expression including therapy response have been noted within a single ethnic group of patients attending the clinic and might account for genetic heterogeneity noted in molecular genetic studies. JME cannot really be called a very 'benign' epileptic syndrome; recurrence after therapy withdrawal almost invariably occurs.

Juvenile myoclonic epilepsy: epidemiology, pathophysiology, and management

Juvenile myoclonic epilepsy (JME) is a common epilepsy syndrome that begins most frequently in the early teenage years. It is officially classified as a type of idiopathic generalized epilepsy and is often under-recognized or misdiagnosed. This syndrome has a strong genetic component with multiple gene mutations being associated with the clinical presentation. Based upon genetic associations, there may be multiple pathophysiologic mechanisms for the disorder; the pathophysiology has not been clearly defined. A diagnosis of JME is made using the clinical history and EEG findings. Valproic acid is the primary antiepileptic drug (AED) used for JME, but some newer AEDs may be effective alternatives. Selection of an appropriate AED is essential to the proper management of JME, because of the possibility of exacerbation of seizures by some AEDs and the adverse effect profiles of effective drugs. It is important for clinicians to understand JME to correctly diagnose and manage patients with this syndrome.

Mutations in the K+/Cl- cotransporter gene kazachoc (kcc) increase seizure susceptibility in Drosophila

During a critical period in the developing mammalian brain, there is a major switch in the nature of GABAergic transmission from depolarizing and excitatory, the pattern of the neonatal brain, to hyperpolarizing and inhibitory, the pattern of the mature brain. This switch is believed to play a major role in determining neuronal connectivity via activity-dependent mechanisms. The GABAergic developmental switch may also be particularly vulnerable to dysfunction leading to seizure disorders. The developmental GABA switch is mediated primarily by KCC2, a neuronal K+/Cl- cotransporter that determines the intracellular concentration of Cl- and, hence, the reversal potential for GABA. Here, we report that kazachoc (kcc) mutations that reduce the level of the sole K+/Cl- cotransporter in the fruitfly Drosophila melanogaster render flies susceptible to epileptic-like seizures. Drosophila kcc protein is widely expressed in brain neuropil, and its level rises with developmental age. Young kcc mutant flies with low kcc levels display behavioral seizures and demonstrate a reduced threshold for seizures induced by electroconvulsive shock. The kcc mutation enhances a series of other Drosophila epilepsy mutations indicating functional interactions leading to seizure disorder. Both genetic and pharmacological experiments suggest that the increased seizure susceptibility of kcc flies occurs via excitatory GABAergic signaling. The kcc mutants provide an excellent model system in which to investigate how modulation of GABAergic signaling influences neuronal excitability and epileptogenesis.

Mechanisms, genetics, and pathogenesis of juvenile myoclonic epilepsy: review

PURPOSE OF REVIEW

This review addresses the mechanisms, genetics and pathogenesis of juvenile myoclonic epilepsy (JME, Janz syndrome).

RECENT FINDINGS

Although JME is a well defined clinical syndrome among the idiopathic generalized epilepsies (IGEs), recent studies suggest that JME is distinct from other IGE syndromes and must be considered separately for the purposes of genetic studies. Clinical, morphological and metabolic data suggest a preferential role for frontal regions in this syndrome. However, JME is clinically and genetically heterogeneous. Although several major genes for JME have been identified and pathogenetic mechanisms suggested based on these findings, these genes account for only a small proportion of JME cases, suggesting multifactorial or complex inheritance in most. The roles played by other major genes, susceptibility genes and environmental factors in the pathogenesis of JME remain to be defined.

SUMMARY

JME is clinically and genetically heterogeneous and should be considered separately from other IGE syndromes. Proposed mechanisms, such as those involving microdysgenesis or altered neuronal inhibition, may be related to different genetic abnormalities in different patients. Major genes account for relatively few cases, and most cases appear to involve multifactorial or complex inheritance.

Genetic Association Studies in Epilepsy: "The Truth Is Out There"

Success has been achieved in identifying many mutations in rare monogenic epilepsy syndromes by using linkage analysis, but dissecting the genetic basis of common epilepsy syndromes has proven more difficult. Common epilepsies are genetically complex disorders believed to be influenced by variation in several susceptibility genes. Association studies can theoretically identify these genes, but despite more than 50 association studies in epilepsy, no consistent or convincing susceptibility genes have emerged, leading to scepticism about the association-study approach. We review the results of existing association studies in focal epilepsies, generalized epilepsies, febrile seizures, and epilepsy pharmacogenetics. By using an illustrative example, we discuss how methodologic issues of sample size, selection of appropriate controls, population stratification, and significance thresholds can lead to bias and false-positive associations; the importance of biologic plausibility also is emphasized. Newer methodologic refinements for association studies, such as use of two control groups, genomic control, haplotyping, and use of two independent datasets, are discussed. A summary of existing guidelines and a checklist for planning and appraising such association studies in epilepsy is presented. We remain cautiously optimistic that with methodologic refinements and multicenter collaborations with large sample sizes, association studies will ultimately be useful in dissecting the genetic basis of common epilepsy syndromes.