Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0036572 (seizures)
 80,221 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

U-54494A, 3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzamide, has been shown to be a potent and long-acting anticonvulsant without analgesic or sedative effects on intact animals. The persistence of anticonvulsant activity after a decline in its concentration in the brain implies the conversion of the parent drug into active metabolites. In this study, two major metabolites of U-54494A, U-83892E [cis-N-(2-aminocyclohexyl)-3,4-dichlorobenzamide] and U-83894A [cis-N-(2-methylaminocyclohexyl)-3,4-dichlorobenzamide], were identified. The synthetic metabolites displayed anticonvulsant activity against electric shock in experimental animals and blocked voltage-gated sodium channel in N1E-115 neuroblastoma cells in voltage- and use-dependent manner by interacting with the inactivated channels as well as with the channels in the resting state (like the parent compound). These observations may provide one explanation for the long duration of the anticonvulsant activity of the parent compound U-54494A and further underscore the importance of voltage-dependent sodium channels in neuronal excitability, especially during seizures.
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PMID:Two metabolites of anticonvulsant U-54494A: their anticonvulsant activity and interaction with sodium channel. 838 24

Generalized epilepsy with febrile seizures plus (GEFS+) is a benign epileptic syndrome of humans. It is characterized by febrile and afebrile generalized seizures that occur predominantly in childhood and respond well to standard antiepileptic therapy. A mutation in the b1-subunit of the voltage-gated sodium channel, linked to chromosome 19q13 (GEFS+ type 1) has been found in one family. For four other families, linkage was found to chromosome 2q21-33 (GEFS+ type 2) where three genes encoding neuronal sodium channel a-subunits are located (SCN1-3A). Recently, the first two mutations were identified in SCN1A. We introduced one of these mutations, which is highly conserved to SCN1A, into the cDNA of the gene SCN4A encoding the a-subunit of the human skeletal muscle sodium channel (hSkm1). The mutation is located in the S4 voltage sensor of domain IV, predicting substitution of histidine for the fifth of eight arginines (R1460H in hSkm1). Functional studies were performed by expressing the a-subunit alone in the mammalian tsA201 cell line using the whole-cell patch clamp technique. Compared to wild-type (WT), mutant R1460H channels showed small defects in fast inactivation. The time course of inactivation was slightly (1.5-fold) slowed and its voltage dependence reduced, and recovery from inactivation was accelerated 3-fold. However, there was no increase in persistent sodium current as observed for SCN4A mutations causing myotonia or periodic paralysis. The activation time course of R1460H channels was slightly accelerated. Slow inactivation was slightly but significantly stabilized, confirming the importance of this region for slow inactivation. The combination of activation and fast inactivation defects can explain the occurrence of epileptic seizures, but the effects were much more subtle than the inactivation defects described previously for mutations in SCN4A causing disease in skeletal muscle. Hence, with regard to pathological excitability, our results suggest a greater vulnerability of the central nervous system compared to muscle tissue.
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PMID:A sodium channel mutation causing epilepsy in man exhibits subtle defects in fast inactivation and activation in vitro. 1111 88

Generalized epilepsy with febrile seizures-plus (GEFS+) is a benign Mendelian syndrome characterized by childhood-onset febrile and afebrile seizures. Three point mutations within two voltage-gated sodium channel genes have been identified so far: in GEFS+ type 1 a mutation in the beta1-subunit gene SCN1B, and in GEFS+ type 2 two mutations within the neuronal alpha-subunit gene SCN1A. Functional expression of the SCN1B and one of the SCN1A mutations revealed defects in fast channel inactivation which are in line with previous findings on myotonia causing mutations in SCN4A, the skeletal muscle sodium channel alpha-subunit gene, all showing an impaired fast inactivation. We now studied the second GEFS+ mutation (T875M in SCN1A), using the highly homologous SCN4A gene (mutation T685M). Unexpectedly, the experiments revealed a pronounced enhancement of both fast and slow inactivation and a defect of channel activation for T685M compared to wild-type channels. Steady-state fast and slow inactivation curves were shifted in the hyperpolarizing direction, entry into slow inactivation was threefold accelerated, recovery from slow inactivation was slowed by threefold and the time course of activation was slightly but significantly accelerated. In contrast to other disease-causing mutations in SCN1A, SCN1B and SCN4A, the only mechanism that could explain hyperexcitability of the cell membrane would be the acceleration of activation. Because the enhancement of slow inactivation was the most obvious alteration in gating found for T685M, this might be the disease-causing mechanism for that mutation. In this case, the occurrence of epileptic seizures could be explained by a decrease of excitability of inhibitory neurons.
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PMID:Enhanced inactivation and acceleration of activation of the sodium channel associated with epilepsy in man. 1142 59

Recent evidence has suggested that the neuronal voltage-gated sodium channel alpha(1)-subunit gene (Na(v)1.1: SCN1A) is responsible for generalized epilepsy with febrile seizures plus (GEFS+2). Here the authors report two novel disease mutations of Na(v)1.1 in patients with febrile seizures associated with afebrile partial seizures. One is a Val1428Ala substitution in the pore-forming region, and the other is Ala1685Val in the transmembrane helix. These results support the previous findings and contribute to the reliable diagnosis of epilepsy.
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PMID:Nav1.1 mutations cause febrile seizures associated with afebrile partial seizures. 1152 84

Two mutations that cause generalized epilepsy with febrile seizures plus (GEFS+) have been identified previously in the SCN1A gene encoding the alpha subunit of the Na(v)1.1 voltage-gated sodium channel (Escayg et al., 2000). Both mutations change conserved residues in putative voltage-sensing S4 segments, T875M in domain II and R1648H in domain IV. Each mutation was cloned into the orthologous rat channel rNa(v)1.1, and the properties of the mutant channels were determined in the absence and presence of the beta1 subunit in Xenopus oocytes. Neither mutation significantly altered the voltage dependence of either activation or inactivation in the presence of the beta1 subunit. The most prominent effect of the T875M mutation was to enhance slow inactivation in the presence of beta1, with small effects on the kinetics of recovery from inactivation and use-dependent activity of the channel in both the presence and absence of the beta1 subunit. The most prominent effects of the R1648H mutation were to accelerate recovery from inactivation and decrease the use dependence of channel activity with and without the beta1 subunit. The DIV mutation would cause a phenotype of sodium channel hyperexcitability, whereas the DII mutation would cause a phenotype of sodium channel hypoexcitability, suggesting that either an increase or decrease in sodium channel activity can result in seizures.
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PMID:Functional effects of two voltage-gated sodium channel mutations that cause generalized epilepsy with febrile seizures plus type 2. 1156 38

Partial or generalized idiopathic epilepsies, which account for up to 40% of all epilepsies, are characterized by a mostly benign course and no apparent etiology other than a genetic predisposition. So far, the genetic defects underlying three different idiopathic epilepsy syndromes have been identified: mutations in the CHRNA4- or CHRNB subunits of the neuronal nicotinic acetylcholine receptor are found in familial nocturnal frontal lobe epilepsy, while defects in the voltage-gated potassium channels KCNQ2 and KCNQ3 have recently been identified in benign familial neonatal convulsions. The syndrome of "generalized epilepsy with febrile seizures plus" can be caused by mutations affecting the voltage-gated sodium channel subunits SCN1B and SCN1A or the gamma 2-subunit of the GABA(A) receptor. The results of recent molecular studies contributed largely to our understanding of the etiology and pathophysiology of idiopathic epilepsies.
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PMID:Genes and mutations in idiopathic epilepsy. 1157 34

Ion channels provide the basis for the regulation of excitability in the central nervous system and in other excitable tissues such as skeletal and heart muscle. Consequently, mutations in ion channel encoding genes are found in a variety of inherited diseases associated with hyper- or hypoexcitability of the affected tissue, the so-called 'channelopathies.' An increasing number of epileptic syndromes belongs to this group of rare disorders: Autosomal dominant nocturnal frontal lobe epilepsy is caused by mutations in a neuronal nicotinic acetylcholine receptor (affected genes: CHRNA4, CHRNB2), benign familial neonatal convulsions by mutations in potassium channels constituting the M-current (KCNQ2, KCNQ3), generalized epilepsy with febrile seizures plus by mutations in subunits of the voltage-gated sodium channel or the GABA(A) receptor (SCN1B, SCN1A, GABRG2), and episodic ataxia type 1-which is associated with epilepsy in a few patients--by mutations within another voltage-gated potassium channel (KCNA1). These rare disorders provide interesting models to study the etiology and pathophysiology of disturbed excitability in molecular detail. On the basis of genetic and electrophysiologic studies of the channelopathies, novel therapeutic strategies can be developed, as has been shown recently for the antiepileptic drug retigabine activating neuronal KCNQ potassium channels.
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PMID:Ion channels and epilepsy. 1157 35

Idiopathic epilepsies, which account for up to 40% of all epilepsies, are mainly caused by genetic factors. Most idiopathic epilepsies are due to oligogenic or multifactorial rather than monogenetic inheritance. Nevertheless, most of what is known today about the molecular genetics of idiopathic epilepsies has been found by analysing large families with rare monogenetic forms of the disease. For the first time, gene defects can be linked to certain epilepsies. Mutations in the CHRNA4 or CHRNB subunits of the neuronal nicotinic acetylcholine receptor lead to familial nocturnal frontal lobe epilepsy, while defects in the voltage-gated potassium channels KCNQ2 and KCNQ3 have recently been found to cause benign familial neonatal convulsions. The voltage-gated sodium channel subunits SCN1B, SCN1A and SCN2A as well as the GABRG2 subunit of the GABA(A) receptor are involved in the pathology of the newly described syndrome generalized epilepsy with febrile seizures plus. These rare monogenetic epilepsies can serve as models for further genetic analysis of the common forms of idiopathic epilepsies.
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PMID:Channelopathies can cause epilepsy in man. 1188 38

Epilepsy is a common neurological condition that reflects neuronal hyperexcitability arising from largely unknown cellular and molecular mechanisms. In generalized epilepsy with febrile seizures plus, an autosomal dominant epilepsy syndrome, mutations in three genes coding for voltage-gated sodium channel alpha or beta1 subunits (SCN1A, SCN2A, SCN1B) and one GABA receptor subunit gene (GABRG2) have been identified. Here, we characterize the functional effects of three mutations in the human neuronal sodium channel alpha subunit SCN1A by heterologous expression with its known accessory subunits, beta1 and beta2, in cultured mammalian cells. SCN1A mutations alter channel inactivation, resulting in persistent inward sodium current. This gain-of-function abnormality will likely enhance excitability of neuronal membranes by causing prolonged membrane depolarization, a plausible underlying biophysical mechanism responsible for this inherited human epilepsy.
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PMID:Molecular basis of an inherited epilepsy. 1208 30

The voltage-gated sodium channel type II alpha polypeptide gene (SCN2A) R188W mutation with channel dysfunction was recently identified in a patient with febrile and afebrile seizures. A possible association between SCN2A R19K polymorphism and febrile seizures (FS) associated with afebrile seizures including generalized epilepsy with febrile seizures plus (GEFS+) was also noted. We attempted to identify the R188W mutation and confirm association of the R19K polymorphism in 93 Japanese patients with FS, 35 Japanese patients with FS associated with afebrile seizures including GEFS+, and 100 control subjects. The R188W mutation was not found. There were no significant differences in genotype or allele frequencies of the R19K polymorphism between groups. Our study failed to provide evidence supporting a causal relation between the SCN2A mutation/polymorphism and FS or FS associated with afebrile seizures including GEFS+ in the Japanese population.
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PMID:Failure to find evidence for association between voltage-gated sodium channel gene SCN2A variants and febrile seizures in humans. 1216 24


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