Two novel mutations in SCN1A gene in Iranian patients with epilepsy

Polymorphisms of the sodium voltage-gated channel, alpha subunit 1 (SCN1A -A3184G) gene among children with non-lesional epilepsy: a case-control study

Background

Mutations in the neuronal sodium voltage-gated channel, alpha subunit 1 (SCN1A) gene have been associated with epilepsy. We investigated the SCN1A-A3184G polymorphism among Egyptian children and adolescents with non-lesional epilepsy.

Methods

A prospective case – control observational study was done in Mansoura University Children’s Hospital, Egypt including 326 children with non-lesional epilepsy (163 antiepileptic drugs (AEDs) resistant cases & 163 AEDs responders) and 163 healthy controls. One step real time polymerase chain reaction (PCR) was used for the molecular analysis. Student’s t-test, and Monto Carlo, chi-square and Mann–Whitney tests were used for the statistical analysis.

Results

All study participants were matched as regards the age, sex and body weight (p = 0.07, 0.347 and 0.462, respectively). They had the (AA) and (AG) genotypes but not the (GG) variant. No significant differences were found between cases and controls regarding (AG) and (AA) genotypes and A- and G-alleles (p = 0.09 and 0.3, respectively). We did not find significant differences between AEDs responders and resistant cases regarding the studied genotypes and alleles (p = 0.61 and 0.746, respectively). In the resistant group, we observed significant associations between the (AG) genotype and seizure frequency (p = 0.05), the tonic-clonic seizure (p < 0.001), the younger age of first seizure attack (p = 0.03), abnormal electroencephalogram (EEG) (p < 0.001), the positive family history of epilepsy (p = 0.006), topiramate (p = 0.03) and valproic acid (p < 0.001), while the (AA) genotype was associated with carbamazepine (p = 0.03). While in AEDs responders, there were significant associations between the AG genotype and the abnormal EEG activity, levetiracetam and carbamazepine (p = 0.016, 0.028 and 0.02).

Conclusions

The SCN1A-A3184G genotypes and alleles were not associated with the epilepsy risk among Egyptian children. Significant associations were reported between the AG genotype and some predictors of refractory epilepsy.

Associations between CYP3A4, CYP3A5 and SCN1A polymorphisms and carbamazepine metabolism in epilepsy: A meta-analysis

BACKGROUND AND OBJECTIVE

CYP3A4 (rs2242480), CYP3A5 (rs776746) and SCN1A (rs3812718 and rs2298771) gene polymorphisms were previously indicated to be associated with carbamazepine (CBZ) metabolism and resistance in epilepsy. However, previous studies regarding the effects of these polymorphisms still remain controversial. Therefore, we performed a meta-analysis to evaluate whether the four polymorphisms are associated with CBZ metabolism and resistance.

METHODS

The PubMed, EMBASE, Cochrane library, Chinese National Knowledge Infrastructure, Chinese Science and Technique Journals Database, China Biology Medicine disc and Wan Fang Database were searched up to January 2021 for appropriate studies regarding the association of rs2242480, rs776746, rs3812718 and rs2234922 polymorphisms with CBZ metabolism and resistance. The meta-analysis was conducted by Review Manager 5.3 software.

RESULTS

Eighteen studies involving 2546 related epilepsy patients were included. We found that the G allele of CYP3A4 rs2242480 markedly decreased the plasma CBZ concentration in epilepsy. For CYP3A5 rs776746 polymorphism, the GG genotype (homozygote codominant model: GG vs. AA) and GG + GA genotype (dominant model: GG + GA vs. AA and recessive model: GG vs. GA + AA) were respectively found to be significantly associated with increased CBZ plasma concentration. Additionally, it was also found that the SCN1A rs3812718 A allele was significantly associated with decreased CBZ plasma concentration and increased CBZ resistance. However, no association was observed between SCN1A rs2298771 polymorphism and CBZ metabolism and resistance.

CONCLUSION

The CYP3A4 rs2242480, CYP3A5 rs776746 and SCN1A rs3812718 polymorphisms may play important roles in CBZ metabolism and resistance, while SCN1A rs2298771 polymorphism is not associated with CBZ in epilepsy. These findings would improve the individualized therapy of epileptic patients in clinics.

Epilepsy-Related Voltage-Gated Sodium Channelopathies: A Review

Epilepsy is a disease characterized by abnormal brain activity and a predisposition to generate epileptic seizures, leading to neurobiological, cognitive, psychological, social, and economic impacts for the patient. There are several known causes for epilepsy; one of them is the malfunction of ion channels, resulting from mutations. Voltage-gated sodium channels (NaV) play an essential role in the generation and propagation of action potential, and malfunction caused by mutations can induce irregular neuronal activity. That said, several genetic variations in NaV channels have been described and associated with epilepsy. These mutations can affect channel kinetics, modifying channel activation, inactivation, recovery from inactivation, and/or the current window. Among the NaV subtypes related to epilepsy, NaV1.1 is doubtless the most relevant, with more than 1500 mutations described. Truncation and missense mutations are the most observed alterations. In addition, several studies have already related mutated NaV channels with the electrophysiological functioning of the channel, aiming to correlate with the epilepsy phenotype. The present review provides an overview of studies on epilepsy-associated mutated human NaV1.1, NaV1.2, NaV1.3, NaV1.6, and NaV1.7.

The possible effect of SCN1A and SCN2A genetic variants on carbamazepine response among Khyber Pakhtunkhwa epileptic patients, Pakistan

PURPOSE

SCN1A (3184 A>G) and SCN2A (56G>A) gene encodes α subunit of the neuronal voltage-gated sodium channel, which is a target for carbamazepine (CBZ). Recent studies have demonstrated that polymorphism of SCN1A (3184 A>G) and SCN2A (56G>A) was associated with use of CBZ. However, it has not been determined whether the polymorphism affects CBZ or other antiepileptic drug responsiveness. The aim of the study was to establish whether the SCN1A (3184 A>G) and SCN2A (56G>A) polymorphisms of the SCN1A and SCN2A genes affect responsiveness to CBZ.

METHODS

SCN1A (3184 A>G) and SCN2A (56G>A) gene polymorphisms were genotyped in 93 Khyber Pakhtunkhwa epileptic patients treated with CBZ. The association between CBZ responsiveness and the polymorphism was estimated by adjusting for clinical factors affecting the outcome of therapy. The number of seizure episodes was documented at baseline, and the therapy of each of the 93 patients was followed up. The plasma level of CBZ was determined using reverse-phase high-performance liquid chromatography. SCN1A and SCN2A genes were genotyped using RFLP. Data were analyzed using Graph Pad Prism 6.

RESULTS

Mean age of the patients was 18.6±9.3 at the 3rd month and 18.7±9.5 at the 6th month. The baseline dose of CBZ was 468±19.8 mg/d and titrated at the rate of 48±1.4 and 4.0±0.2 mg/d. The difference in plasma level of CBZ was significant (P=0.004) between 3rd and 6th month among different genotypes of SCN1A gene in nonresponder and responder patients. At the 3rd month of the therapy, the poor responders were more likely (P=0.003 and P=0.01) to have variants (3184AG and 3184GG) of SCN1A gene. Similarly, poor responsders were more likely (P=0.0007 and P=0.001) to have variant genotypes (56GA, 56AA) of SCN2A gene at the 3rd month of the therapy.

CONCLUSION

This study demonstrated a significant association between the SCN1A (3184 AG and GG) and SCN2A (56GA and AA) genotype with CBZ-nonresponsive epilepsy.

Pathogenic significance of SCN1A splicing variants causing Dravet syndrome: Improving diagnosis with targeted sequencing for variants by in silico analysis

OBJECTIVES

Genetic heterogeneity of epileptic encephalopathy (IEE) mandates the use of gene-panels for diagnosis.

PATIENTS AND METHODS

A 36-gene-panel next-generation sequencing was applied for IEE in two Iranian families. A literature search was performed using keywords to identify reported splicing mutations in SCN1A and perform genotype-phenotype correlation.

RESULTS

An update of splicing mutations revealed 147 variants with 65.75% of them de novo mutations. Most of the familial variants were of parental origin. The structure of the protein was often affected in the linker and transmembrane segments. 92% of intronic variants were pathogenic. A de novo heterozygous mutation was found in the first patient, but not in her sibling and parents. In the second family, a novel de novo heterozygous mutation was found at position c.1210insT leading to a truncated protein.

CONCLUSION

Gene-panel sequencing is helpful for reducing the time and cost, guiding early treatment, and estimating the recurrence risks. The importance of characterization of intronic variants was noticed; though bioinformatics analysis of novel intronic variants should be of concern for rapid reporting the pathogenic effect of variants.

The association of SCN1A p.Thr1067Ala polymorphism with epilepsy risk and the response to antiepileptic drugs in Slovenian children and adolescents with epilepsy

PURPOSE

The voltage-gated sodium channel SCN1A mutations are involved in epileptogenesis and may be associated with different epilepsy phenotypes. The SCN1A channel is also an important antiepileptic drug (AED) target. The aim of this study was to investigate if the SCN1A c.3184A>G/p.Thr1067Ala polymorphism modifies the epilepsy risk or is associated with the responsiveness to AEDs in Slovenian children and adolescents with epilepsy.

METHODS

In total, 216 paediatric patients with epilepsy were consecutively recruited during routine outpatient follow-up visits between January 2011 and December 2014. All patients and 95 healthy controls, all Central European Caucasians, were genotyped for the SCN1A c.3184A>G/p.Thr1067Ala polymorphism. Clinical data on all patients were collected retrospectively. The response to AEDs was classified as seizure remission (a minimum of one year of seizure freedom before inclusion) or no remission. Univariate and multivariate logistic regression was used to determine the association of genotypes with binary outcomes.

RESULTS

114 patients (52.8%) had achieved remission, while 102 (47.2%) had failed to do so. Carriers of at least one polymorphic SCN1A c.3184A>G/p.Thr1067Ala G allele tended to have a lower epilepsy risk (OR=0.38, 95% CI=0.18-0.79, P=0.010) and were significantly more likely to achieve remission (OR=2.00, 95% CI=1.16-3.46, P=0.013). Girls were less likely to achieve remission (P=0.055). Patients in remission tended to be older at first seizure in comparison to the group failing to achieve remission (OR=1.06, 95% CI=0.99-1.14, P=0.099), but this association did not reach statistical significance.

CONCLUSION

The polymorphic SCN1A c.3184A>G/p.Thr1067Ala G allele was associated with a lower risk of epilepsy and a higher remission rate in Slovenian children and adolescents with epilepsy.

The potential implication of SCN1A and CYP3A5 genetic variants on antiepileptic drug resistance among Egyptian epileptic children

PURPOSE

Despite the advances in the pharmacological treatment of epilepsy, pharmacoresistance still remains challenging. Understanding of the pharmacogenetic causes is critical to predict drug response hence providing a basis for personalized medications. Genetic alteration in activity of drug target and drug metabolizing proteins could explain the development of pharmacoresistant epilepsy. So the aim of this study was to explore whether SCN1A c.3184 A/G (rs2298771) and CYP3A5*3 (rs776746) polymorphisms could serve as genetic based biomarkers to predict pharmacoresistance among Egyptian epileptic children.

METHODS

Genotyping of SCN1A c.3184 A/G and CYP3A5*3 polymorphisms using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was performed in 65 healthy control subjects and 130 patients with epilepsy, of whom 50 were drug resistant and 80 were drug responsive.

RESULTS

There was a significant higher frequency of the AG genotype (p=0.001) and G allele (p=0.006) of SCN1A polymorphism in epileptic patients than in controls. Also their frequency was significantly higher in drug resistant patients in comparison with drug responders (p=0.005 and 0.054 respectively). No significant association between CYP3A5*3 polymorphism and drug-resistance was found.

CONCLUSIONS

Overall, results confirmed the claimed role of SCN1A c.3184 A/G polymorphism in epilepsy and moreover in development of pharmacoresistance among Egyptian epileptic children. CYP3A5*3 variants have no contributing effect on pharmacoresistance among Egyptian epileptic children.