Failure to find evidence for association between voltage-gated sodium channel gene SCN2A variants and febrile seizures in humans

Role of SCN2A c.56G/A Gene Polymorphism in Egyptian Children with Genetic Epilepsy with Febrile Seizure Plus

BACKGROUND

Febrile Seizures (FS) are the most common seizures in children younger than 5 years. In the last decade, various coding and noncoding sequence variations of voltage-gated sodium channels SCN2A have been identified in patients with seizures, implying their genetic base. We aimed to evaluate the association between SCN2A c. G/A genetic polymorphism among Egyptian children with febrile seizure plus.

METHODS

The present cross-sectional study was carried out on 100 epileptic infants and children, attendants of the Neurology Unit, pediatric department, Menoufia University Hospitals (Group Ι). The patients were sub-classified into two groups, according to response to anti-epileptic treatment; Group Ι a (drug responder) and Group Ι b (drug-resistant). Evenly divided number of apparently healthy, age and gender-matched children were selected as controls (Group II). A complete history, throughout the systemic examination and radiological & metabolic assessment, whenever needed was provided, all participants were genotyped for SCN2A rs17183814 polymorphism by Restriction Fragment Length Polymorphism (PCR-RFLP).

RESULTS

Both of A allele and AA, GA genotypes of SCN2A c. 56 G/A were detected more in patients with febrile seizure plus comparison to the control group with a statistically significant difference at frequencies of 17% and 11% and 12% respectively; OR (CI95%): 10.04 (3.49-28.87) and p <0.001. On classifying epileptic patients into 2 subgroups, carriers of SCN2A rs17183814 AA genotype tended to respond poorly to Anti-epileptic Drugs (AEDs). Moreover, multivariate analysis revealed that rs17183814 A allele and positive family history of epilepsy were considered the highest predicted risk factors for the development of epilepsy; p<0.05.

CONCLUSION

SCN2A rs17183814 (A) allele was specifically associated with developing febrile seizure plus and could modulate the patient's response to anti-epileptic medications.

Lack of association of SCN2A rs17183814 polymorphism with the efficacy of lamotrigine monotherapy in patients with focal epilepsy from Herzegovina area, Bosnia and Herzegovina

OBJECTIVE

We assessed the influence of the SCN2A gene polymorphism c.56 G > A rs17183814 on the response to lamotrigine monotherapy in patients with focal epilepsy in Herzegovina area, Bosnia and Herzegovina.

MATERIAL AND METHODS

For SCN2A polymorphism c.56 G > A rs17183814, one hundred patients with epilepsy who were receiving lamotrigine in monotherapy and seventy-one age and sex matched healthy controls were genotyped using TaqMan assay. All patients were Caucasians from the region of Herzegovina, Bosnia and Herzegovina. Genotyping was conducted using a polymerase chain reaction in real time. Patients were divided into two groups: responders and non-responders.

RESULTS

Of all patients with epilepsy, 33% were non-responders, and 67% were responders. The mean age of non-responders was 38.8 vs. group of responders in which it was 35.2. Mean age of onset of seizures in epilepsy patients was 26.7 for non-responders and 25.4 for responders. In patients with epilepsy, the mean age of seizure onset was 26.7 for non-responders and 25.4 for responders. For SCN2A c.56 G > A gene polymorphism, we did not observe any significant differences in genotypic or allelic frequency between patients with epilepsy and healthy controls. Genotype or allelic frequencies of SCN2A c.56 G > A gene polymorphism did not significantly differ for AG or GG genotypes in the non-responders vs. responders.

CONCLUSION

There was no significant association in patients with focal epilepsy between studied genotypes and response to lamotrigine monotherapy in Herzegovina patients with focal epilepsy. However, we need studies in a bigger cohort of patients with epilepsy to be assessed in the future.

Chemotherapy-induced peripheral neuropathy: What do we know about mechanisms?

Cisplatin, oxaliplatin, paclitaxel, vincristine and bortezomib are some of the most effective drugs successfully employed (alone or in combinations) as first-line treatment for common cancers. However they often caused severe peripheral neurotoxicity and neuropathic pain. Structural deficits in Dorsal Root Ganglia and sensory nerves caused symptoms as sensory loss, paresthesia, dysaesthesia and numbness that result in patient' suffering and also limit the life-saving therapy. Several scientists have explored the various mechanisms involved in the onset of chemotherapy-related peripheral neurotoxicity identifying molecular targets useful for the development of selected neuroprotective strategies. Dorsal Root Ganglia sensory neurons, satellite cells, Schwann cells, as well as neuronal and glial cells in the spinal cord, are the preferential sites in which chemotherapy neurotoxicity occurs. DNA damage, alterations in cellular system repairs, mitochondria changes, increased intracellular reactive oxygen species, alterations in ion channels, glutamate signalling, MAP-kinases and nociceptors ectopic activation are among the events that trigger the onset of peripheral neurotoxicity and neuropathic pain. In the present work we review the role of the main players in determining the pathogenesis of anticancer drugs-induced peripheral neuropathy.

Differential role of sodium channels SCN1A and SCN2A gene polymorphisms with epilepsy and multiple drug resistance in the north Indian population

AIMS

To evaluate sodium channel genes as candidates for epilepsy susceptibility and their role in therapeutic efficacy, we screened coding single-nucleotide polymorphism of SCN1A p. Thr 1067 Ala or c.3184 A-->G (rs2298771) and SCN2A p.Arg19Lys or c.56 G-->A (rs17183814) in north Indian epilepsy patients.

METHODS

The genotyping was performed in 160 control subjects and 336 patients with epilepsy, of whom 117 were drug resistant and 219 were drug responsive. Therapeutic drug monitoring for phenytoin, carbamazepine, phenobarbital and valproate was also performed in 20% of the patients to confirm compliance.

RESULTS

AG genotype of SCN1A 3184 A-->G polymorphism was significantly higher and associated in epilepsy patients [P= 0.005; odds ratio (OR) 1.76, 95% confidence interval (CI) 1.19, 2.61], whereas A variant of SCN2A c.56 G-->A was associated with multiple drug resistance in north Indian patients with epilepsy (P= 0.03; OR 1.62, 95% CI 1.03, 2.56).

CONCLUSIONS

Overall, results indicate a differential role of genetic polymorphisms of sodium channels SCN1A and SCN2A in epilepsy susceptibility and drug response.

Genetic susceptibility to febrile seizures: case-control association studies

OBJECTIVE

A genetic predisposition to febrile seizures (FS) has long been recognized. The inheritance appears to be polygenic in small families or sporadic cases of FS encountered in daily clinical practice. To determine whether candidate genes are responsible for the susceptibility to FS, we have performed genetic association studies in FS patients and controls.

METHODS

The single-nucleotide polymorphisms (SNPs) of genes involved in immune response (interleukin (IL) 1B), endocannabinoid signaling (CNR1), acid-base balance (SLC4A3, SLC9A1, SLC9A3), gap junction channel (CX43), and GABA(A) receptor trafficking (PRIP1) were examined in 249 FS patients (186 simple and 63 complex FS) and 225 controls.

RESULTS

There were no significant differences in the allele frequencies of the SNPs between controls and all FS, simple FS, and complex FS patients. When the simple FS patients were divided into two groups according to either having (familial) or not having a family history of FS in close relatives (sporadic), there was a significant association between IL1B -511 SNP and sporadic simple FS (p=0.003).

CONCLUSIONS

These data suggest that cytokine genes may act as enhancers or attenuators of FS susceptibility. Genetic association study may be an effective approach to understanding the molecular basis of FS at least in a subgroup of patients.

Genetic variants in microsomal epoxide hydrolase influence carbamazepine dosing

OBJECTIVES

The dose of carbamazepine required to achieve optimal seizure control varies widely from patient to patient. We investigated polymorphic variants in various genes involved in the pharmacokinetics and pharmacodynamics of carbamazepine in an effort to identify predictors of maintenance dose.

METHODS

: A total of 70 patients with epilepsy (49% were males; median age, 34 years; range, 14-72 years) who had benefited (>50% reduction in seizure frequency for at least 12 months) from treatment with carbamazepine monotherapy were included in the analysis. Known variants in drug-metabolizing enzyme genes, including those encoding cytochrome P450s, uridine 5'-diphosphate-glycosyltransferase, and microsomal epoxide hydrolase, together with a sodium channel polymorphism in SCN2A, were screened using polymerase chain reaction-restriction fragment length polymorphism or direct sequencing. Associations between demographic and genetic variables and carbamazepine dose were identified by univariate and multivariate regression analyses.

RESULTS

All genotype frequencies were consistent with Hardy-Weinberg equilibrium (P > 0.05). No single demographic or genetic variable was of sufficient strength to independently influence carbamazepine dosing requirements. However, a multivariate model, incorporating patient age and specific genotypes (c.337T>C, c.416A>G) of the EPHX1 gene encoding microsomal epoxide hydrolase, revealed a significant association with the maintenance dose of carbamazepine (r(2) = 0.362, P= 0.002).

CONCLUSIONS

This proof-of-principle study suggests that genetic variants in EPHX1 can be used to predict maintenance doses of carbamazepine. A large-scale prospective investigation of genetic influences on drug dosing strategies in epilepsy, with specific focus on whole gene variability for those proteins involved in the pharmacokinetics and pharmacodynamics of antiepileptic agents, is warranted.

Progress in searching for the febrile seizure susceptibility genes

Febrile seizures (FS) represent the most common form of childhood seizures. They affect 2-5% of infants in the Caucasian population and are even more common in the Japanese population, affecting 6-9% of infants. Some familial FS are associated with a wide variety of afebrile seizures. Generalized epilepsy with febrile seizures plus (GEFS+) is a familial epilepsy syndrome with a spectrum of phenotypes including FS, atypical FS (FS+) and afebrile seizures. A significant genetic component exists for susceptibility to FS and GEFS+: extensive genetic studies have shown that at least nine loci are responsible for FS. Furthermore, mutations in the voltage-gated sodium channel subunit genes (SCN1A, SCN2A and SCN1B) and the GABA(A) receptor subunit genes (GABRG2 and GABRD) have been identified in GEFS+. However, the causative genes have not been identified in most patients with FS or GEFS+. Common forms of FS are genetically complex disorders believed to be influenced by variations in several susceptibility genes. Recently, several association studies on FS have been reported, but the results vary among different groups and no consistent or convincing FS susceptibility gene has emerged. Herein, we review the genetic data reported in FS, including the linkage analysis, association studies, and genetic abnormalities found in the FS-related disorders such as GEFS+ and severe myoclonic epilepsy in infancy.

Oxaliplatin-induced coronary artery spasm: first report of an important side-effect

A 67-year-old woman with metastatic colorectal cancer was given her first oxaliplatin infusion as part of the XELOX protocol. She developed chest pain with ECG changes leading subsequently to a diagnosis of coronary artery spasm. To our knowledge, this is the first report of oxaliplatin-induced coronary artery spasm.

Association analysis of gamma2 subunit of gamma-aminobutyric acid (GABA) type A receptor and voltage-gated sodium channel type II alpha-polypeptide gene mutation in southern Chinese children with febrile seizures

We attempted to identify the prevalence of the R188W mutation of the SCN2A gene and the K289M mutation and single-nucleotide polymorphism rs211014 of the GABRG2 gene in children of southern China who have febrile seizures. Neither mutation was found in our subjects. The single-nucleotide polymorphism rs211014 AA genotype was overrepresented in the febrile-seizures group compared with controls (62.4% vs 29.0%). The single-nucleotide polymorphism rs211014 A allele was higher in the febrile-seizures group (P < .005). Compared with the single-nucleotide polymorphism rs211014 CC genotype, the odds ratio for developing febrile seizures in individuals with the single-nucleotide polymorphism rs211014 AA genotype was 4.05 (P < .005). A new mutation of C-to-T transition was found at nucleotide 81719 of the GABRG2 gene in a 5-year-old boy, suggesting that the above mutations may not be the main disease mutations. The single-nucleotide polymorphism rs211014 A allele may predict susceptibility to febrile seizures.

Oxaliplatin-related neurotoxicity: how and why?

In early clinical trials, oxaliplatin has demonstrated significant activity against colorectal cancer in combination with 5-fluorouracil (5-FU) and folinic acid (FA), both in metastatic as in radically resected disease. The drug differs from the other two most important platinum compounds (cisplatin and carboplatin) for the absence of nephrotoxicity or for the reduced drug-induced ototoxicity. During its administration, two different types of neurological symptoms can be experienced: the first one occurs during or immediately after the end of the infusion and it appears as a transient peripheral sensory neuropathy manifesting as paresthesias and dysesthesia in the extremities sometimes accompanied by muscular contractions of the extremities or the jaw (triggered or enhanced by exposure to cold). The second one occurs after long-term administration of oxaliplatin presenting with deep sensory loss, sensory ataxia and functional impairment (similar to those observed with cisplatin). This type of neurotoxicity is usually late-onset and correlated with the cumulative-dose of oxaliplatin. The aim of this review is to analyse the mechanism underlying induction of neurotoxicity and the possible treatments to prevent and to treat it.

Polymorphisms of casein kinase I gamma 2 gene associated with simple febrile seizures in Chinese Han population

Casein kinase I gamma 2 isoform (CSNK1G2), a member of the large casein kinase I (CKI) family, may affect the development of brain, and associate with vesicular trafficking and neurotransmitter releasing from small synaptic vesicles. Based on our previous linkage analysis data that mapped our simple febrile seizures (FS) families to 19p13.3 and the function of CSNK1G2 in this region, CSNK1G2 was chosen as a candidate gene for FS. All of the 13 exons and their flanking introns of the CSNK1G2 gene were amplified and sequenced, and 10 single nucleotide polymorphisms (SNPs) were found. Using the three SNPs we found as markers, we conducted association studies in 60 FS patients and 101 normal controls. Allele and genotype frequencies of the SNPs IVS2-33C > T and 837C > T as well as the haplotype of the two SNPs were significantly different between FS patients and controls (P < 0.05). This study suggests that CSNK1G2 gene may be a susceptibility gene for FS in the northern Chinese Han population.

Seizure phenotypes of a family with missense mutations in SCN2A

The seizure phenotypes of a Japanese family with missense mutations in SCN2A are described. The proband of the family had partial epilepsy after febrile seizures plus. He had three missense mutations of SCN2A (R19K, R188W, and R524Q). The R188W mutation was suggested by electrophysiologic studies to be the main disease mutation. However, it is suggested that the penetrance rate of this pedigree is extremely low, or that other genes may have modified the phenotype of the proband.

Failure to find causal mutations in the GABA(A)-receptor gamma2 subunit (GABRG2) gene in Japanese febrile seizure patients

Recently, mutations in the GABA(A)-receptor gamma2 subunit (GABRG2) gene were identified in two families with generalized epilepsy with febrile seizures plus (GEFS+) and two families with childhood absence epilepsy (CAE) and febrile seizures (FS). We tested the hypothesis that genetic variations in the GABRG2 gene confer susceptibility to FS in the Japanese population. We performed a systematic search for mutations in 94 unrelated Japanese patients with FS and detected six variants (-158C>T, 315C>T, 588T>C, IVS5-55C>T, IVS7+20G>A, and IVS7-141T>A). No non-synonymous mutation was detected. We genotyped three exonic polymorphisms and performed a case control study and a transmission disequilibrium test using 55 independent complete trios with FS and 106 control subjects. None of these polymorphic alleles were significantly associated with FS. Our results indicate that genomic variations of GABRG2 are not likely to be substantially involved in the etiology of FS in the Japanese population.